1. business and industrial
2. agriculture and forestry
3. aquaculture

PROJET REGIONAL MEDITERRANEEN DE
DEVELOPPEMENT
DE L'AQUACULTURE
MEDITERRANEAN REGIONAL AQUACULTURE PROJECT
PRODUCTION IN MARINE HATCHERIES
ROVINJ - ZADAR (Yugoslavia - 10-28 Feb. 1986
Edited by
Brigide LOIX
MEDRAP
Juin 1987
CONTENTS
1. GENERAL PRESENTATION
1.1 Introduction
1.2 Development of the session
1.3 Acknowledgements
2. CONFERENCES
3. ANNEXES
3.1 Fry production in hatcheries : programme
3.2 List and addresses of the participants
3.3 List and addresses of the lecturers
1. GENERAL PRESENTATION
1.1 Introduction
The ninth training session, organized by MEDRAP, in collaboration with the
MIRNA in ROVINJ, and CENMAR in ZADAR on the theme "Fry production in hatcheries"
was held in yugoslavia from the 10 to 28 February 1986 (Annex 1).
The first part of the seminary based principally on a theoretic approach, was
welcomed by the MIRNA company in ROVINJ. The second part was based on practical
experiments of the CENMAR hatchery in ZADAR.
1.2. Development of the session
a) The participants (Annex 2)
Twenty participants from 9 different countries of MEDRAP took part at this
session. Twenty Yugoslavian people also participated at some of the lectures.
As recommended by MEDRAP nearly, all of the participants has already
acquired good experience on the subjects in question either through public or private
sectors which permitted good level of exchange of points of view.
b) The lecturers (Annex 3)
Seventeen lecturers from eight different countries animated the first part of the
seminary in ROVINJ. During this period, practical work was also carried out by some
people from MIRNA.
The second part held in ZADAR, was animated by 3 lecturers along with the
CENMAR personnel who developed the methods employed in theory for each sector of
the hatchery and illustrated these methods through practical worK.
c) Development of the conferences
Each lecturer had two hours at disposal (including translation) to present his
subject and answer any first question. At the end of every afternoon, a round table
reunited the lecturers and participation and permitted an exchange of information on the
experience of each of the countries present.
1.3. Acknowledgments
In thanking most sincerely the lecturers for their competence and the participants
for their enthusiasm, we would like to express a
special thanks to the MIRNA and
CENMAR companies who greatly contributed to the success of the session.
We should also like to extend of hearthy thanks to the MEDRAP personal who
took charge of the translation, typing and editing of the texts for this
session.
II. CONFERENCES
II CONFERENCES
1. Fish and shellfish culture in the LIM canal. Present and future pilot farm
rearing.
Mr. Z. FILIC, Ms. Hrs. BRENKO, I. IVANCIC
2. Marine Aquaculture : Experience of the CENMAR
p. 9
p. 33
3. Marine fish hatcheries : site - production programme - dimensioning.
Mr. L. BERG p. 37
4. Marine fish hatcheries : Structures - equipment - economical aspects.
Mr. G. BRUNEL p. 49
5. The conception of "Intensive type" fish rearing facilities with partial or total
water regeneration
Mr. J. PETIT p. 61
6. Use of thermic discharges
Mr. P. BRONZI p. 73
7. Production of phyto and zooplankton
Mr. G. FANCIULLI p. 99
8. Microorganisms used in aquaculture. The natural zooplankton yield.
Mr. A. PONTICELLIp. 115
9. Increased yields of marine fish and shrimp production through application of
innovative techniques with Artemia.
Mr. P. SORGELOOS, Ph. LEGER, P.LAVENS, W. TACKAERTp. 131
10. International study on Artemia. XlII. Ihe effect of the nutritional quality of
Artemia on the growth and survival of sea-bass (Dicentrarchus Jabrax) larvae
in a commercial hatchery.
Mr. V. FRANlCEVIC, D. LISAC, J. BUBLE, Ph. LEGER, P. SORGELOOSp. 139
11. Reproduction and larval rearing of peneids .
Mr. F. LUMAREp. 147
12. The production of shrimp post - larvae : the present situation of hatchery
Penaeus japonicus.
Mr. G DE MOULAO, O. DE LA POMELIEp. 181
13. Larving rearing of bivalve molluscs.
Mr. G. ROMANp. 189
14. MULLET : Artificial propagation.
Mr, C. NASH, R.M. KONINGSBERGERp. 225
15. Tilapia culture.
p. 247
Mr. C. AGIUS
16. Larval rearing, weaning and firt fattening of sole and turbot.
Mr. B. MENUp. 256
17. Fry producing techniques of red-sea-bream. Pagrus major, in Japan.
Mr. C. KITAJIMAp. 272
18. Four marine spawners in European hatcheries.
Ms. N. DEVAUCHELLEp. 302
19.
Larval shrimp feeding : crustacean tissue suspension : a practical alternative
for shrimp culture
Mr. A.G.J. TACONp. 348
FISH AND SHELLFISH CULTURE IN THE LIM CANAL
PRESENT AND_FUTURE _PILOT_ FARM REARING*
* Remark: The article has been published in “Food and Development”, edited in “La Yougoslavie en developpement”.
Mr. Z. FILIC, Ms. M. HRS-BRENKO and l. IVANCIC
The exploitation of marine resources is becoming a technique of the present, due
to the lack of energy. Apart from the fact that the sea is exploited, so as to obtain fuel,
liquid and gas minerals, it has also become a food source of much greater importance.
In this report, we shall give a description of the technological aspects and the rearing
techniques employed in the Lim Canal, as a possible example for intensive rearing in our
part of the Adriatic.
1. INTRODUCTION
In comparison to the exploitation of land, the aquatic space area is rather poorly
exploited, especially as the latter makes up 71 % of the terrestrial surface area (rivers,
lakes, seas and oceans). While with land exploitation, only the surface is employed for
production, in the sea the whole space area can be exploited, in other words, a three
dimension system. It has been calculated that 1 to 1,5 of food comes from the sea while
the rest is obtained from the land (1). In 1984, the production of consumable organisms
from aquatic environments was 76 million ton (2). There exists two means of increasing
the production and of satisfying the market requirement in sea protein: the promotion
and intensification of fishing and the production of marine organisms through
aquaculture (3). The problems arising in fishing are well known and it is not easy to
introduce its intensification, as apart from the technological and technical problems and
those of organization (the fishing activity), the principle obstacle is, in fact, the limited
resources of the sea, due to the fact that the fishing zones bear very severe and
complicated laws. Fishing, by which means 90 % of consumable organisms are
produced, has significant limits of development: Thus, we must increase the production
through rational sea-exploitation, the most effective being fishculture with the
employment of intensive rearing techniques, in fresh and marine water. According to
PILLAy (4), through aquaculture (fresh and brackish water), 67 % of fish. 16.5 % of
molluscs, 16 % of algae and 0.5 % of crabs are produced.
Unpolluted protected coastal zones are reserved to rear consumable organisms
for commercial purposes. With as objective an economic exploitation and the
conservation of the quality of aquatic environment, the simultaneous rearing of two or
several species such as fish-fish, fish-crustaceans and other combinations are employed
more and more to-day. It has been remarked that the shells reared in polyculture, with
different species of fish or shells, reach a commercial value more quickly and present a
better quality meat. This is due to the surplus phyto-planktonic organisms and dissolved
waste matter (faeces) from fish, plus the nutritive salts after decomposition of the food
uneaten by the fish. In this way, the shells maintain,a biological and chemical balance of
the aquatic environment, there where intensive rearing is employed. A permanent
control of the organisms reared and of the aquatic environment is advisable, especially,
in tanks and shallow closed -in regions with feeble exchange of water masses.
Our coast being well indented, with more than 6,000 km of coastal strips, offers
real possibilities to practice the mass rearing of different species of marine organisms,
which can satisfy our own requirements, as well as those of exportation.
This sea-food production was introduced into the economy of our country.
Shellfish rearing, after a long stagnation (300 -- 500 t/y) shows a tendency to increase
the production, with 1,200 ton in 1984 and 1985. (2, Statistic Institute of the Socialist
Republic of Croatia). Commercial fish rearing (sea-bass, trout, salmon) was started in
several localities along the coastline and on parallel intensive research was carried out
on fish, shells and crabs while taking into account, their ecology, their physiology and the
rearing technologies (5, 6).
The Lim Canal, one of our prized regions has been dedicated to mussel and
oyster rearing for a long time. Some years ago, after the successful results obtained with
the experimental rearing of sea-bass (7), the building of a pilot farm was undertaken in
the interior part of the canal, along with the research of the biological characteristics of
the fish and shells, the fundamental hydrographical, chemical, and biological parameters
of the marine environment (8). The pursuit of the control of the organisms and of the
marine environment is scheduled. This has been included within the next national and
international research programme.
This report will not only take into account the description of the rearing
techniques employed for fish and shellfish, but also, the actual state of the organisms in
culture and of the environment, in comparing present data with that obtained through
anterior research works.
2.. THE LIM CANAL AS A REARING SITE
The Lim Canal was decreed as a special sea-reserve for intensive shellfish and
fish culture. It is located on the West coast of Istria, to the North of ROVINJ and
measures around 11 km. The banks of the Canal are indented and covered with
autochthonal vegetation. The width at the inlet is around 160 m and decreases little by
little up to the extremity. The depth of one third of the canal is around 34 m while at its
extremity it descends to 5 m.
The rearing site at present, occupies the interior half of the canal (Figure 1) and
active rearing is carried out at surface level and at a depth of 3 to 4 m. In the shallow
part of the Canal, can be seen fixed parts, consisting of a series of wooden poles which
are embedded into the bottom soil and linked to one another by means of ropes, on
which the shellfish rearing takes place (Ro "SKOLJKA", POREC) (Figure 2). Towards
the center of the Canal, in the deep parts (more than 10 m in depth) is found the parksfloating longlines (series of plastic floats attached to one another by means of "Atlas"
ropes (Figure 3). Next to the floating parks, we find the cages with fish nets, on the
outside of which hang strings of beads (mussels) and plastic baskets (oysters) (Ro
"MIRNA", ROVINJ) (Figure 7).
3. SHELLFISH CULTURE
It was in 1888 that oyster rearing on beechwood branches was first started in the
inner part of the Canal. The succes in the production of oysters (up to 7 million
oysters/year) reared in floating parks, was ensured during the period between the two
world wars (9). Towards the end of 1950, mussel rearing was introduced into the Lim
Canal and other Adriatic sites along the coast and a greater production has always been
obtained when compared to oysters (2, 10). An important production of shells from the
Lim Canal was finally obtained in 1984, 600 tons of mussels and l50 tons of oysters
(Statistic Institute of the Socialist Republic of Croatia).
3.1. The technology employed in mussel rearing, Mytilus gallo-provincialis
The rearing of mussels begins with the collection of spat from natural
environments by means of collectors (flexible plaited ropes). The ropes are placed
horizontally between the poles or the floats, in the park, at a depth of 10 to 30 cm below
the surface of the sea (Figure 3 c).
Intensive collection of mussels lasts from March to the end of May (11). In
Autumn, small mussels (2 - 4 cm in length) are detached and threaded onto plastic tubelike nets (Figure 4). In the Lim Canal, the mussels reach commercial size in 1 ½ to 2
years (8, 12). It is possible to cultivate 8 to 15 kg of commercial size mussels in a tubelike net of 1,7 to 2 meters in length (Figures 2 a, 4 b). Mortality is insignifiant during the
rearing of the mussels but however it does increase in the hot season.
3.2. The technology employed in oyster rearing, Ostrea edulis
Bundles of branches (10 to 20 branches) are employed for the capture of
oysters. These are connected to one another by means of nylon strings or beech or elm
wood branches (Figure 4 c, d). To-day, plastic plates are also employed (20 x 20 cm)
through which a nylon rope is threaded and this is connected to the floating ropes or to
the sides of the cages (Figures 3 a - 4 c).
The season for spat oyster collection lasts from June to October (11). If the
collection is poor, the spat oysters are left on the branches which will be cut up into
sticks of 20 to 30 cm and which are threaded onto a nylon string (Figure 4 F) . When the
collection is good, the oysters are selected out and detached from the branches or
plates, and they are then cemented or placed into plastic baskets. The oysters are
cemented, with quick Setting cement, either to ropes or onto large strips of netting, in
twos or in fours or again in twos at the end of each branch (Figure 4 g, h. i . j). Oysters
can also be cemented to nylon ropes which are attached to the park (Figure 2, b, c, d).
The baskets containing the shells are suspended by means of ropes from the floating
park, one by one or several at a time, one on top of the other (15) (Figure 3 b). Our
oysters reach commercial size in 2 to 2 ½ years while the Japanese oyster reaches this
size in less time. The oyster mortalities can rech up to 18% and from time to time, in
certain sites, up to 70 % (12, 14). At the present, in our sites, a sufficient amount of spat
oysters, can be collected for commercial rearing. Nevertheless, when necessary, the
existing capacities of the fish hatchery can be employed to rear young oysters (15).
The shellfish culture methods carried out in the Lim Canal are also employed in
our other rearing centers with some slight; modifications. The perspectives are good for
the development of shellfish culture, thanks to the advantage that we avail of and to the
improved technologies in rearing, especially mussels, alone or with fish, leads to an
increase in sea food along with an assured marketing supply for home and foreign
markets, and the processing industry. The technology of oyster rearing which is
expensive and more complicated, requires development in certain technological
procedures so as to increase production.
4. THE PARAMETERS FOR THE CONTROL OF THE REARING ENVIRONMENT AND
OF THE MUSSELS
In modern rearing, the knowledge of the basic physical,chemical and biological
parameters of the aquatic world is absolutely necessary so as to control and adapt the
rearing to the environmental conditions.
In addition to the standard hydrobiological measures for the requirements of the
rearing and for the quality control of the organisms, it is advisable to control the quality of
the water and of the commercial shells, as there is a potential danger of pollution due to
the faecal bacteria from fresh water.
4.1. Hydrography of the Lim Canal
The Lim Canal is a site which has important fresh water intakes. The fresh water
flowing into it generally comes from shallow coastal sources ; the underground water of
the central part of Western Istria, along with biologicaly purified waste water from
restaurants located on the banks of the Canal. The influence of the fresh water is
unpredictable and very changeable, from surface and time points of view, but generally
this concerns only the upper layers (less the 2,5 m deep) where important variations in
parameters and in the rearing have been, remarked.
The hydrographical and chemical characteristics in the other side of the water
column are much more homogeneous and undergo fewer variations. In this layer, the
hydrographical and chemical parameters vary in the characteristic divergences for
oligotrophic coastal waters in ROVINJ (Table 1). However, in the superior layer of the
Canal, when the sea water is freshened, the nitrate concentrations are rather high. The
distribution of the superficial nitrate concentrations, in June 1986 (L-1 - L-5) indicated
that this increase, remarked in the whole canal is greater in the last third where the
salinity values at surface level are at their lowest level (Figure 8). However, in August
1986, the nitrate concentrations were equalled, even if they remained a little superior in
the surface layer. The drop in the surface salinity, which was remarked in August, in
comparison to the inferior layers, was not provoked by fresh water inflows, but was the
consequence of a decrease in salinity, which at that period, was typical in the whole
North Adriatic. The analysis of the report which has been followed up for years, between
the salinity and the nitrate concentrations in the surface layer confirmed that the greatest
part of these salts come from fresh water. The estimation of the nitrate concentration in
the fresh waters which flow into the Lim Canal also shows that the quantity of these
waters has greatly increased when compared to previous periods. This shows that the
superior concentrations of nitrate in fresh water, recently remarked, are of anthropogenic
origin. This, has been confirmed by the periodical apparition of a green superficial layer,
provoked by the blooming of fresh water algae (FILIPIC, not edited). This has not been
remarked for ammonia, nitrite and orthophosphate, which have the same divergences in
concentrations in the superior layer as in the other part of the water column (Table 1).
4.2. The quality control of shells
To control the quality of the shells (meat content), we employ mussels (because
they intensively filtrate sea water) of commercial size (between 55 and 65 cm in length)
which at the end of Summer, reach a maximum value of Condition index (8). At the end
of July , strings of commercial mussels were placed into 9 different sites, in the canal
(Figure 1). Mussels, at points 5 and 6, were attached to the fish cages. We wanted to
find out if the condition index for the mussel, increased on account of the fish food. The
condition index is calculated by means of the volumetric method (20). Over a relatively
short period (1.5 mois), the C.I of the mussels located near the fish and those far away
showed no difference (Table 2), as with the value obtained before (HRS BRENKO, 1967
; BOHAC i Sur, 1984).
The parameters of the marine environment and of the mussels did not
demonstrate great changes during the period of stratification in Summer (June - August
1986). However, it is advisable to maintain the same bearing capacity while assuring a
permanent control of the marine environment which can be unpredictable and at certain
periods, unexpected changes can have catastrophic, consequences.
5. FISH REARING
Fish rearing, dates back to ancient times. The first doctorate written on
aquaculture was presented in 475 B C by FAN LI (22, 23). The traditional extensive and
semi-intensive fish rearing takes place in lagoons (Valliculture), near VENICE, in canals
where many different species are reared : mullet (Mugil sp), Sea-bream (Sparus aurata),
sea-bass (Dicentrarchus labrax) and eel (Anguilla anguilla and according to RIEWAGEN
(24) a production of 200 kg/year is obtained.
In the seventies, we witnessed the rapid development of fish rearing in teh sea,
with the introduction of cage rearing for salmonidae. The modern cages of to-day were
first introduced in 1986, in Scotland, the best results were obtained by Japan with the
Yellowtail (Seriola quinqueradiata) and by Norway with the salmon (25, 26). In Norway,
already 15,000 t/year of Salmonidae are produced and in 1990, it is scheduled that a
production of 20,000 ton of trout and salmon will be obtained (Onchorhinchus kisutch,
Salmo gairdneri, S. salar (27, 28).
Following the intensive research carried out in Yugoslavia, very important
experiments in sea-bass cage rearing were performed at the end of the seventies and
the beginning of the eighties, when the commercial rearing of sea-bass was introduced
into the Lim Canal and at the Lamljani near ZADAR (3, 29, 30, 31). At the mouth of the
river Krk and in the Bay of Zrnovnica, trout rearing was introduced, followed by salmon
rearing (32, 33). At ZADAR, fish rearing in cages rapidly increased due, to the opening
of the industrial hatchery for fish in NIN (34).
5.1. Cage-rearing of fish as a perspective for rearing in the Adriatic
Rapid progress was made in marine fish rearing after the first successful results
obtained with the control]ed reproduction of sea-bass and the juvenile rearing in France
and Italy, at the beginning of the seventies (35, 36, 37).
In 1976, the first successes were obtained with the induced spawning of seabass, carried out at the Sea-research Center in ROVINJ, and the complete experimental
hatchery production and cage rearing in the Lim canal occured in 1978 (3).
5. 2. Pilot farm for sea-bass rearing in the Lim Canal
As an example of cage rearing for marine fish in the Adriatic, let us consider the
technical data on the sea-bass rearing farms which are employed by the marinculture
Center of the "MIRNA" Society in ROVINJ, in the Lim Canal. The farms are built in
accordance with the projects by FILIC/PLESE (1983) and FILIC LEDERER (1984)
(Figures 6, 7).
The typical characteristic of these plat-form cages is that they are very robust
which makes them expensive. This is considered necessary for security reasons, as
when a complete production is carried out, the value of the fish in the cages is 5 to 7
times greater than the value of each plat-form. The cages and farm, due to their form,
construction and materials are adapted to the rearing technology employed for sea-bass
and to the site.
TECHNICAL AND TECHNOLOGICAL CHARACTERISTICS OF THE FARM
Volume of the cages
Number of the cages
Capacity of a cycle
Unitary capacity
Quantity of fry at the beginning of
the cycle
Quantity of fish at the end of the
cycle
Feed
Material : Construction
Floats
Plat-form
Cages
Length of the farm
Number of persons necessary
150 m3
16 (18)
18-27 ton
1-1.6 ton
0.13 Kg/m3
8 - 10 Kg/m3
Eminced fish and dry pellet
Galvanized steel
Polyethylene filled with expanded polystyrene
Wood
Nylon nets, meshes 5, 10, l6 mm
120 m
3
The cages are formed of 4 segments which can be employed separately, and
can be easily separated from the farm (Figures 6, 7). In addition, to its rectangular
shape, the principal characteristic of the "MIRNA" farm model is its canals (free spaces
between the segments). We think that this is important in a rearing with closed bays,
where currents are feeble (4 to 5 cm/sec). In such conditions, the maximum quantity of
sea-bass, according to the experiments carried out in the Lim Canal, is around 8 to 10
kg/m3. This is a fish rearing where the environment is no different (surplus metabolites)
from the marine environment outside the cages. The same density is obtained in cage
rearings in Southern France (Thau pond) and in Japan (38, 39).
To obtain a continuous production of fish, over a two year cycle, it is necessary to
have at disposal two of these systems for an annual production of 18 to 27 ton. The farm
is equipped with a watchman's quarters, a warehouse and a platform pier, where the
work can be carried out. Three people are quite sufficient to take charge of the fish
rearing of the farm.
A particularly interesting possibility is the combination of shells and fish in rearing
(polyculture) (Figure 7) which rationalizes time, space and work and leads to a quicker
depreciation of the rearing facilities and as has been specified here above in the
introduction, this type of rearing also improves the quality of the marine environment.
The negative side of polyculture is that spat shells can catch on to the nets, especially
when the environment is one for collection.
In addition to large system rearing, linked with industrial hatchery rearing, the
farms can be individually, privately or cooperatively owned, all along the whole coast.
The fry can be fished, or obtained from large hatcheries. At present we have but one
hatchery in operation and it is located at NIN, while another one is being built in the Lim
Canal.
The farms must be implanted in good sites and when possible, they must answer
the following requirements : protection from waves and winds, good currents and deep
bottoms.
This is why, sites of good potential are required, their hydrographical and
biological characteristics defined and the most favourable place determined.
An example of this space planning is shown in Figure 8, where shell culture is
carried out in the shallow eutrophic part of the Lim Canal, and the fish rearing, in the
deepest and vastest part, with the best water exchange. This space planning, scheduled
for rearing, is the result among other things, of the previous ecological research of the
site and the verification of the technical and technological parameters of the rearing.
During the commercial rearing, it is essential that the parameters of the rearing
environment be surveyed so as to remark possible changes before its too late and which
could, in the later case, decrease the efficiency of the, rearing
(FUJIVA, 1976 ; LUCET et al., 1984).
We consider that the implantation of such a rearing or a similiar one along the
coast, will lead to the more rapid development in sea-fish and shell rearing in
Yugoslavia.
6. CONCLUSIONS AND RECOMMENDATIONS
Within the frame of sea fishing, in addition to the fishing development, based on
the rational exploitation of fish populations, the rearing of sea organisms must also be
developed and particularly fish and shellfish culture.
Fish and shellfish rearing represent a programmed and controlled view of fishing
which could, through its production, reach the results obtained in fresh water fishing
(around 40,000 t/year).
The implementation of a rearing programme is possible, as far as, our knowledge
and the technologies employed, are concerned. However, for this, it is necessary to
organize an energetic economical and scientific public action for the promotion of the
rearing (based on the economic indicators) by creating special financial organization
conditions along with other conditions of development.
In addition to that,, two important resources must be available, the human and
natural resource. Through the intermediary of science, public instruction and economy,
an efficient collaboration must be established, so as to form experts who will be capable
of taking in charge, the production and development. The principal factor which limits the
development, is the unavailability of marine sites of quality, which must be quickly
protected and the harmonization of conflicting interestS (urban environments, tourism,
industry, rearing). Tourism and rearing can, for example, be directly complementary to
one another as producer and consumer of high quality food and thus decrease the
present importation of around 20,000 ton of white fish.
In addition to the direct finanacial effects of the increase in the consumption of
fish and shellfish, there are important socio-economical and health reasons for the most
rapid development of fishculture. Fish and shellfish are a very wholesome food and from
a nutrition view-point a complete food which contains all the necessary materials for the
development of the human organism, thus their consumption will lead to an improvement
in the health of the population.
By encouraging fishculture and creating mass rearings, we shall influence the
stabilization and improvement of the socio-economical and demographical structures of
the coastal populations and Islanders.
Fish rearing is an annual activity and not a seasonal one, it will thus decrease a
part of the migrations (seasonal) of populations.
As fish rearing is a biotechnical activity in particular it is very complex and
requires the permanent development of the rearing techniques which will influence the
general level of instruction of the population concerned by fish rearing.
To conclude, by linking the economic existance of the population with rearing,
people shall realize the necessity of conservation, promotion and rational exploitation of
a healthy marine environment.
We think that this is absolutely necessary, not only because the Adriatic is
considered as the "most beautiful sea", but because we wish to save it from degradation
and preserve it for future generations as we have not inherited this natural patrimony
only for its exploitation during our short biological existance.
Figure 1 :Site of the Lim Canal.
Rearing site L-l - L-5 Hydrography 1-9 Mussel (Condition index)
Figure 2 : Fixed park (Italian)
Figure 3 - Part of a rearing park - Line
Figure 4 : Shellfish culture combined with fish rearing
Figure 5 : Pilot-farm f'or marine fishculture, "MIRNA" model.
Figure 6 : General view of the farm
Legend
1. Elements of the farm
2. Warehouse
3. Watchman’s quarters
4. Shed
5. Wharf
6. Power press
7. Feeders
8. Stairs
9. Signal lights
10. Rails
11. Rope connections
12. Armouring for the fixation of the nets
13. Anchors and anchor armouring
Figure__7 : Presentation of the urbanization of the rearing site in the Lim Canal
Figure 8 : Distribution of the salinity and nitrate values in the site of the Lim Canal in June and August 1986
DESCRIPTION OF THE FIGURES
Figure 1 : Site of the Lim Canal.
Rearing site, Place from where the samples
are taken : L-1 - L-5 (Hydrography), 1-9 (Condition index of the mussels).
Figure 2 : Fixed park (Italian make) (a - netbag with mussels, b, c, d -- Cemented
oysters).
Figure 3 : Floating park (a - oyster collector, b - oyster basket, c - mussel collector).
Figure 4 : Culture during the rearing of the shells (a, b - mussels in the net-bag, c, d, e oyster collectors, f - spat oysters on branches, g, h, i, j -cemented oysters).
Figure 5 : Pilot farm for marine fishculture - "MIRNA" model (1 - Watchman quarters and
warehouse, 2 - Platform, 3 - boat, 4 - cages)
Figure 6 : General view of the farm (1 - elements of the farm, 2 - Warehouse, 3 Watchman quarters, 4 - Shed. 5 - Wharf, 6 - Power press, 7 - Feeders, 8 stairs, 9 - Signal lights, 10 - Rails, 11 - Rope-connections, 12 -Armouring for
the fixation of the nets, 13 - Anchors and anchor armouring)
Figure 7 : Presentation of the urbanization of the rearing site in the Lim Canal.
Table 1 - Value of the fundamental oceanographical parameters and of the nutritive salts
in the Lim Canal and on the coastal region of ROVINJ.
THE LIM CANAL
Parameters
COASTAL WATER ROVINJ
+
1
2
1
2
T/0C.
9.8-24.5
9.1-23.1
12.1-24.4
11.7-23.8
Sal (‰)
9.5-38.2
34.7-38.4
34.2-38.O
36.9-38.3
O2 %
8o-137
54-113
93-138
63-123
PO4
o.o2-l.oo
0.02-0.26
o.o2-o.l3
0.01-0.15
NH4
0.0-2.1
0.1-2.4
0.1-1.5
0.0-1.3
NO2
0.03-l.70
0.00-l.80
0.02-0.75
o.o2-o.75
NO3
0.5-78.1
0.2-H.o
0.3-1.7
1.3-9.5
+ Sal( ‰) salinity, 02 % of oxygen saturation, PO4 Ortophosphate, NH4 Ammonia, NO2 nitrite, NO3 Nitrate, u μmol. 1
+ Data obtained from 1978 to 1985 on part 4 of the Lim Canal 1 - Surface layer, 2 - Rest of the water column.
- Data obtained from 1978 to 1983 on 8 places along the coast of ROVINJ, including the site in front of the port of
ROVINJ. 1. Surface layer, 2 - Rest of the water column.
-1
Table_2 - Biometrical characteristics and the condition index of mussels (between 55
and 65 mm in length), in the Lim Canal on the 21 August. 1986.
Average wet Weight (g)
Whole mussel - shell meat
Average dry
Weight (g) Shell
meat
Riviera +
20.9
8.0
4.5
7.7
1.0
4.1
13.3
Condition
index
according to
BAIRDS%
30.8
Vieux
Radeau
17.6
7.4
3.8
7.0
0..7
3.7
13.6
27.2
Parc Plaža
18.9
7.3
3.7
6.9
0.7
3.0
13.6
22.1
Nouveau+
Radeau
18.5
6.5
3.3
6.2
0.6
3.4
13.0
26.2
Ferine
croissan.
17.6
6.6
3.2
6.1
0.7
3.2
11.5
28.2
Ferme
Geniteurs
19.2
6.9
3.5
6.6
0.7
3.3
12.9
25.6
Karigader
17.3
6.7
3.2
6.3
0 .6
3.0
11.2
26.8
ČerižeraI
18.9
7.1
4.2
6.7
0.9
3.8
12.8
29.7
Šimija+
16.6
7.2
3.6
6.8
0.7
3.5
13.6
25.7
+ The samples were taken from the park as the strings had disappeared.
Average volume
(ml) Meat
BIBLIOGRAPHY
Alessio, G., Bronzi, P., Gandolfi, G. Schreiber, B., Rend. Scient., B-107: 93-106, 1973.
Barnabe, G. , Tourmamille, J. , Rav. Trav. Inst. Pêches Maritimes, 36(2) : 85-189, 1972.
Basioli, J., Pomorski zbornik, 6 : 176-216, 1968.
Bchač , M., Hrs Brenko, M, Labura, Ž ., Filić Ž., Bilten društva ekologa B i H, serija B (2)
: 321-325, 1984.
Filić, Ž., Haliotis, 5, 196-205, 1975/76.
Filić, Ž Morsko ribarstvo, 30 :145-151, 1978.
Filić, Ź, Pojed, I, III konferencija SITH o tehnološkom razvoju SR Hrvatske, Zbornik
radova, knjiga III : 179-188, 1979.
Filić, Ž Pojed, I., Morsko ribarstvo, 32 : 22 - 26, 1980.
Fujiva, M. FAO Technical Conference on Aquaculture 1976, Advances in Aquaculture 9
453 - 458, 1979.
Ghittino, P. (ed), Tecnologia e patologia in acquacoltura. Vol. I Technologia, 1983.
Hrs-Brenko, M., Thalassia Jugosl., 3 : 173-178, 1967.
Hrs-Brenko, M., Acta Adriat., 16 (7) : 125 - 136, 1974.
Hrs-Brenko, M, III konferencija SITH o tehnološkom razvoju SR Hrvatske. Zbornik
radova, Knjiga II, PP 16, 1979.
Hrs-Brenko, M., Nova Thalassia, 4 (suppl.) : 67-85, 1980.
Hrs-Brenko, M., Pomorski zbornik, 23 : 217-236, 1985.
Hrs-Brenko, M. , Ž Filić, Stud. Rev. GFCM, (52) : 35 - 45, 1973.
Lucet, Ph., Balma, G., Bonfils, J., L Aquaculture du Bar et de Sparides, INRA Publ. (ed),
pp 381-394, Paris, 1984.
Milne, P.H. Fish and Shelfish farming in coastal waters, Fishing News Ltd. (ed), London,
1972.
Pillay, T.U.P., FAO/Conf/1976/, 36 : pp 13, 1979.
Ravagnan, G. , Elementi di vallicultura moderna, Edagricole (ed), pp 238, Bologna,
1978.
Teskeredžić, E., Morsko ribarstvo, 35 : 16-17, 1983.
Teskeredžić, E., Morsko ribarstve, 36 : 67-71, 1984.
Vik, K.O., Salmon and Traut Mag., 196 : 203-208, 1986.
Vodopija, T., Morsko ribarstvo, 32 : 14-17, 1980.
Vodopija, t., Morsko ribarstvo, 36 : 53-59, 1984.
MARINE FISH FARMING_ -_THE CENMAR EXPERIENCE
Sea-bass can be considered as the first marine fish species successfully cultured
from egg to market size in the Mediterranean region. A young company, CENMAR, is
amongst the first to have mastered the reproduction and intensive culture of sea-bass on
a commercial scale. An outline of the steps leading to this, and a presentation of today's
involvment in mariculture activities will be given.
HISTORY
In 1976, the Institute for Biotechnology in ZADAR began the first trials with cage
culture for sea-bass employing imported hatchery fry. Results were good ; the fish
reached 300 g after 18 months culture, and the survival rate was 70 %. The trials were
repeated successfully over the following years, with initial stocking of cages limited to a
maximum of 50,000 fry of 3 cm due to low availability. Being one of the most valuable
finfish in the Mediterranean (retailed at around 20 US dollars), sea-bass farming became
an attractive financial venture. The Yugoslavian coastline with hundreds of Islands and
deep bays is ideally suited for intensive cage culture both at industrial and family scale.
A prerequiste for the expansion of this activity is to ensure a reliable and steady
supply of fry. To secure this, the construction of a hatchery was obligatory. A temporary
company was formed to organize and carry out the construction of this building,
HATCHERY CONSTRUCTION
In 1980, the projects for a hatchery with a capacity of 1,400,000 sea-bass fry
were completed. It was not until 1982 that the levelling of the site began, after all the
funds (loans and credits) were secured.
Constructing the hatchery and equipping it took almost a year and a half. This
also involved adaptations and redesigning of original plans during the implementation.
By Summer 1983, the building works were terminated, and the first culture phases of
phytoplankton began. In January 1984, the hatchery was technologically functional and
the first: fish eggs were seeded. The hatchery was constructed and equipped entirely
with domestic materials.
At the same time, CENMAR became an independant company. As such, it is
entirely self-financed.
HATCHERY OUTLINE
The hatchery building covers an area of 5,000 m2 and it is the largest marine
hatchery in Europe. It is located within a reasonably-insulated building, to minimize heat
loss during Winter months. The sea water is heated above 20° C and recirculated within
the hatchery for faster growth and energy conservation.
Operating the hatchery (totalizing 250 tanks) requires a strict control on sanitary
and water quality parameters, timely balanced feeding, and a reliable live food culture.
This can be achieved only by employing dependable manpower at the work and
guidance/supervision levels. It also requires standby auxiliary equipment, such as
pumps and electricity generators in the event of breakdowns, even of very brief duration.
PRODUCTION RESULTS
The first production season was completed in July 1984, with a production of
1,100,000 fry, which were almost all stocked in our own cages. During this running-in
season, assistance was obtained from the F.A.O (Technical Cooperation Programme)
through expert help and equipment for the chemistry and pathology laboratories .
The following year production increased to 2 million fry and another species, seabream, was included. This was a major step forward in our effort to double the hatchery
production Capacity through constant technological improvments.
It is planned to achieve this without any major new investments but through a
more intensive exploitation and the introduction of other fish species.
A detailed analysis of the first two production seasons was made and the
strategies for further development set up.
ONGROWING EXPERIENCE
On parallel to the initiation of the hatchery project, the experimental work with
cage culture continued.
In 1980, a pilot facility was set up at a new location, in Lamjana Bay on the island
of Ugljan. This site was chosen for its more favourable sea water temperature range
(min. 11° C, max. 25° C), better water circulation, lower organic productivity and
reasonable protection from high seas.
During this pilot phase (1980 - 1984), a number of biotechnological parameters
affecting marine fish culture were investigated.
CAGE DESIGN
Fourteen different types of cages were tested thoroughly for characteristics of
stability, wave-resistance, corrosion-resistance, ease of maintenance and repair, easy
assembly, compatibility with husbandry requirements (communication between cages,
net changing, safety). By the end of 1983, it was not difficult to decide on the present
model for the merit of sea-worthiness coupled with confortable use and low
maintenance. The cage platform is constructed with a modular frame of hot-galvanised
tubes, styrofoam floats, wooden walkway all around, and can accomodate either one net
of 9.5 x 9.5 m or four nets of 4.5 x 4.5 m. It was manufactured in a local shipyard to our
specifications.
BIOTECHNOLOGICAL ASPECTS
A variety of fish species were cultured from hatchery and wild fry including
Sparus aurata, Puntazzo puntazzo, Mugilidae, Diplodus sargus, Boops salpa, Diplodus
vulgaris, Lithognathus mormyrus, apart from the initial Dicentrarchus labrax. Of the high
value species, Puntazzo show the best growth and survival in cages, followed by S.
aurata and D. labrax.
Both dry and wet feeds were tested, and a number of dry feeds compared. There
is often a greater variation between batches from the same producer than between
different producers. This is shown by a mass mortality (over 80 %) of fish, in Summer
1982. The cause was a batch of food from a producer who had previously supplied a
good quality product.
Fish density in cages is a fundamental factor in determining the bioeconomy of a
culture operation. We found that crowding fish to densities of 20 kg/m3 results in
decreased growth rate and feed conversion efficiency. Pathological problems and risk of
oxygen depletion increase when nets became fouled and in periods of calm weather with
little water circulation .
The major cause of mortality in cages were outbreaks of Vibrio. These were most
pronounced at the beginning of Summer and in Autumn, affecting year old fish. 40 % of
the stock was sometimes lost. A Vibrio vaccine was tested, but by 1984, a more effective
treatment was found ; properly timed prevention with sulpha-drugs. The effectiveness of
this is increased by good husbandry; varied food, clean nets, low stocking densities.
Losses from Vibrio are now below 5 %.
The cage culture ongrowing complex was completed in 1984. The shore facility
comprises a building (1,000 m2), housing a 50 ton freezer unit, a dry food store, net
store, net repair shop, workshop, laboratory, offices, and social rooms. Ahead, is a jetty
for landing boats, cleaning nets, feed preparation section, auxiliary services.
Presently, we have 150 cage platforms of 10 x 10 m, situated in two different
locations of the bay, one for each year class. A third location will also be exploited,
giving flexibility and possibility to allow regeneration of the sea substrate. The presence
of almost 400 ton fish in the bay and the food input has led to the local increase in
organic productivity, which is exploited by increased shellfish and wild fish biomass.
STAFFING
CENMAR employs ten full-time mariculture specialists. The production manager
is backed by a hatchery and a cage manager. The hatchery is divided into four main
sections : live food, reproduction and pathology, larvae and fry, water circulation quality,
each headed by one specialist. The cage unit similarly has a fish production and a
pathology specialist. The research and development section is being formed, and
presently employs one feed specialist. A minimum of two trainees are always employed,
allowing key personnel to undertake research and development activities.
COMMERCIAL ASPECTS
Market size fish are in preference sold abroad because of the higher prices
obtained than on the domestic market, and the need of obtain foreign currency so to
import dry feeds and other materials. Apart from market size fish, we have export and
import trade of live fish eggs, larvae and fry.
New regulations on foreign investments in Yugoslavia do not limit foreign
participation in financing and management. The low cost of labour and materials,
coupled with a good technological basis, expertize, and favourable environmental
conditions make the Yugoslavian coast an attractive site for joint ventures in mariculture
production. One joint venture arrangement with a Norwegian company is already under
way.
MARINE FISH HATCHERIES
SITE - PRODUCTION PROGRAMME - DIMENSIONING
Mr. L. BERG
1. SITE CHOICE
In most cases, the choice of the site for the construction of a hatchery is directly
related with the existence or planning and relative requirements of an on-growing farm
(sea-cages, extensive lagoon rearing, integrated intensive rearing projects).
Therefore the criteria for the choice of the site mostly depend on the on-growing
stage. Criteria generally considered for the site choice of a marine hatchery are as
following :
1.1 Socio-economic aspects
This is important in the particular case of an integrated project : hatchery + ongrowing. Any new aquaculture activity must be perfectly adapted to the economic and
social context of the country and the area chosen for the project.
The market possibility and conditions must be taken into account in relation with
the site :
–
Transport possibilities and costs to local fish markets or to foreign markets
–
Possibility of direct sale to consumers (I.E. restaurants)
–
Sale prices of the fish produced
–
Daily/weekly/monthly quantities that can be absorbed by the market
–
Impact of costs of raw-materials and labour.
1.2. Water supply and water quality
The water quality is a basic factor for the site choice and the productivity of a
hatchery. The chemical and physical properties of the water directly influence the results
of hatchery productions as well as the production costs of fingerlings. For the
reproduction of marine species, marine water is needed, especially for gonadal
maturation and so as to ensure high quality sexual products (fertilized and viable eggs).
Three kinds of water supply can be found, on general :
–
Direct supply from the sea
–
Supply from a marine lagoon
–
supply from an underground salt water sheet.
When a sea or lagoon water supply is employed, particular attention must be
paid to the following factors : bathymetry (water depths, streams, tides).
When underground water is employed, the water flow capacity must be
previously established. Frequently underground water is poor or completely void in
oxygen and iron or ammonia concentrations are at lethal levels for fish.
Generally lagoon waters have to be avoided because of the high and fast
variability of some basic factors : temperature, salinity, oxygen, pH, algal blooms.
On general, the following parameters have to be analysed and correspond to the
specific requirements of fish,
–
temperature,
–
salinity,
–
oxygen,
–
ph,
–
ammonia, nitrites and nitrates,
–
phosphates and silicates,
–
eventual pollution sources (heavy metals, pesticides, insecticides).
Most of these factors can be easily controlled and manipulated at the entrance of
the hatchery or at the water recirculating systems level inside the hatchery.
1.3. Building permissions and eventual restrictions
The site must be chosen in accordance with the possibility of obtaining
permission for the implementation of the hatchery building, the pumping station or any
other construction works and the waste water discharge network systems.
The various restrictions connected with local or national rules and laws in matters
of building projects have to be taken into consideration during the stage of site choice for
a hatchery.
It can happen that buildings, which already exist, can be positively used for a
hatchery project, thus reducing the requests of permissions and also the building costs.
1.4. Proximity of raw materials, labour supply and basic networks
The most direct and nearest supply of raw materials and spare parts for the
hatchery is one of the most important criteria for the site choice. The management of the
hatchery also takes advantage from the possibility of finding labour staff in the proximity
of the hatchery, thus reducing travelling time losses for staff and facilitating emergency
interventions when required.
Raw materials must be obtainable from the area where the project is to take
place, thus increasing the availability efficiency and reducing production costs. The site
must offer the possibility of good communication with the various networks : roads,
electricity power, freshwater, telephone. The distance of the chosen site to the various
networks will directly define the investment costs of the hatchery,
1.5. Proximity of the place of destination for fingerlings
When a site has been defined for the on-growing of fish, the hatchery must be
built as close as possible to the on-growing site.
In all events, the transport of fingerlings for a period of 24 hours doesn't present
any difficulty and can be carried out while causing little or no harm to the fish.
The distance between the hatchery and farm will directly influence the costs of
finger lings for on-growing.
1.6. Environmental factors
Climatology and meteorology can also influence the choice of a hatchery site,
even if the hatchery activity is carried out in sheltered buildings and therefore protected
from the meteorological conditions. For example, the wind conditions and the annual air
temperature evolution will determine the kind of building to be built (concrete, greenhouses) and the degree of thermic insulation needed.
The topography and pedology must be studied for the preliminary ground
preparation and the design of the hatchery building.
1.7. Eventual existence of economic or social facilities
Particular facilities can be offered by some local administrations or national plans
for defined areas in order to improve and develop specific industrial activities.
2. PRODUCTION PROGRAMMES
A marine hatchery must be designed for the reproduction of various species, thus
exploiting different periods during the year and increasing the production capacity of the
hatchery.
At the present time, in the Mediterranean area, three marine species can be
successfully reproduced on industrial scale in a hatchery while using the same basic
frameworks :
–
Sea-bass (Dicentrarchus labrax) : December - March
–
Sea-bream (Sparus aurata) : October - February
–
Shrimp (Penaeus japonicus) : March - June.
For Sea-bass and Sea-bream, these are the natural reproduction periods. The
hatchery production capacity can be furthermore increased and ensure staggered
spawning. In employing these techniques which have been performed in France over the
past years (See DEVAUCHELLE's paper), it is possible to obtain spawning during the
whole year. The problems arising with fingerlings coming from staggered spawnings is
that the juveniles are of small size when Winter arrives. In some Northern Mediterranean
areas, small size juveniles will have to be kept in indoor tanks during Winter because of
the low water temperatures. Shrimp reproduction can be carried out throughout the
whole year, but generally hatchery programmes plan their spawnings in Spring time so
that post-larvae can benefit by the maximum time of favourable thermic conditions for
the on-growing stage (one season rearing cycle).
Figure 1 shows an example of a five cycle production programme for a marine
hatchery in the Mediterranean. The Spawning season begins in October (1st cycle) for
sea-bream and fingerlings generally must be kept inside the hatchery until February March, because of the low water temperatures (Northern Mediterranean), In December,
the sea-bass spawning season begins and the hatchery programme can include seabass as well as sea-bream fingerling production. (2nd cycle). During the second cycle,
there will be a superposition of the nursery stages of 1st and 2nd cycle (January February) and of 2nd and 3rd cycle (March). This aspect must be taken into
consideration when calculating the number of tanks needed for the nursery (See part 3).
In January, the 3rd cycle begins (sea-bass and/or sea-bream). In March, the hatchery
programme can include sea-bass as well as shrimp reproduction (4th cycle). Generally,
at this time, the natural spawning season has finished for sea-bream. A last cycle (5th)
could be carried out with the staggered spawning techniques.
This programme is based on a specific hatchery technology and can therefore
vary, in relation with the methodology used for the hatchery production. In the present
case, larval rearing is carried out at 20° C in cylindro-conical tanks (2 m3 capacity) until
the larvae reach 45 days of age. At this stage, the larvae are transferred from larval
rearing tanks to nursery tanks (10 to 15 m3 capacity).
3. DIMENSIONING OF A HATCHERY
The main activity sectors of a marine hatchery are :
1. Breeder and spawning tanks
2. Phyto-zooplankton unit
3. Larval rearing tanks
4. Nursery tanks
The rest of the hatchery premisses consists in the technical and service units :
–
Heating-refrigeration unit
–
Electricity room, generator
–
Workshop and store-room
–
Food stocking and preparation unit.
–
Laboratory and office
–
Services (wc, bed-room, kitchen)
The figures below show the dimension of each sector in a hatchery having a
production capacity of 2,000,000 sea-bass fingerlings/year.
m2
%
Breeding
225
10
Phyto-zooplankton
180
8
Larval rearing
300
14
Nursery
650
29
Other premisses and free spaces
850
39
2 205
100
Units
Total
The kind and size of technical and service premisses needed for a hatchery can
vary in accordance with the specific conditions and requirements of a given project. For
example, some of these premisses (workshop, generator, laboratory, office, kitchen) can
be used in common by the rest of the farm or other facilities.
The size of both the larval rearing and nursery unit will be in proportion with the
size of the hatchery (capacity), whereas, in percentage, the size of the breeding and
plankton unit will increase if the hatchery capacity decreases.
3.1. Breeding and spawning unit.
This unit includes the following tanks :
1. Indoor and outdoor stocking (In Northern Mediterranean indoor stocking of
sea-bream is necessary ) 50 - 100 m3 capacity tanks for stocking densities
varying from 2 (Summer) to 5 kg/m3 (Winter).
Broodstock needed (For each million fingerlings/year capacity)
* Sea-bass : 250 kg ; sex-ratio ; 2 : 1
* Sea-bream : 150 kg ; sex-ratio : 1 : 1
2. Conditioning tanks for staggered spawning (See DEVAUCHELLE's report)
3. Spawning tanks
at least 4 tanks of 5-10 m3 capacity each.
3.2. Phyto-zooplankton unit
For each million of fingerlings/year capacity of the hatchery, the following daily
plankton production capacities are needed (See table).
Examples of the kind of culture containers and total volumes needed are also
reported.
Plankton
Daily production
needed (maximum)
Kind of container
Unitary volume
of container
Total needed
volume
Algae
100 l of concentrated
culture
Plastic bags
Fiber glass/
concrete tanks
140-400 l
10 - 50 m3
5-7
-
Rotifers
500,000,000 ind.
Cylindro-conical
tanks
Fiber glass/
concrete tanks
2 m3
20
10 - 50 m3
-
0.5 - 2 m3
6
Artemia
500,000,000 ind.
Cylindroconical
tanks
For algae and rotifers culture, large volumes (10-50 m3) can be used in addition to the
normal containers. For this purpose un-used breeder tanks or nursery tanks can be
temporarily used.
3.3. Larval rearing and nursery tanks
3.3.1. Initial Figures
The following table shows the various figures involved in the calculation for the
number of tanks needed for larval rearing and nursery. The initial and fixed figures are
as following :
a) Yearly production of fingerlings needed
The present example is based on a production of 1,000,000 sea-bass
fingerlings/year
b) Number of production cycles of the hatchery
Example : 3 cycles/year (a staggered spawning cycle is not included
here)
c) Survival rates of larvae and fingerlings
–
For larval rearing (from egg stage to 45 day old larvae) : 25 %
–
For nursery stage (from 45 day old larvae to 1 g fingerlings): 75
%
d) Stocking densities of larvae and fingerlings
For the capacities calculations, the final density has to be considered :
–
For 45 day old larvae : 10/000 individuals/m3
–
For 1 g fingerlings : 3,000 ind/m3
e) Unitary volumes of tanks
In this example, we have chosen the following tanks
–
Larval rearing : 2 m3 capacity tanks
–
Nursery : 10 m3 capacity tanks
3.3.2. Steps of calculation
–
Total yearly production : 1,000,000 fingerlings
–
Total production of fingerlings per cycle (3 cycles)
–
initial number of larvae in nursery per cycle (75 %) :
–
Final number of larvae in larval rearing tanks per cycle : 440,000
–
Initial number of eggs per cycle (25 %):
–
Total number of eggs needed per year: 1,760,000 x 3 cycles =
5,280,000
–
Total larval rearing tank volume per cycle:
–
Total larval rearing tanks per cycle:
–
Total larval rearing tanks in the hatchery (separated cycles): 22
–
Total nursery tank volume per cycle:
–
Total nursery tanks per cycle:
–
Total nursery tanks in the hatchery (superposition of 2 cycles) : 11 x 2
= 22 tanks.
(1) If the exterior water temperatures permits the transfer of 1st cycle fry, the number of
weaning tanks necessary will be 11 instead of 22.
stages N. of Length Initial N. Survival Final (3) Total fin
Final
TANKS(m3)
cycles of of ind. per rate
N. of N. of ind. density(4) Tota1 Unitary N. Total
(1 per cycle
cyc1e
ind. per per year (ind/m3 ) vol. volume per
(5)
year Months
cycle
per
cycle number
(2)
cycle
Larval
3
1.5 1,760,000 25 % 440,000 1,320,000 10,000
44
2
22
22
rearing
1.5 Nursery 3
440,000 75% 330,000 1,000,000 3,000
110
10
11
22
2.5
Notes :
(1) Without staggered spawning
(2) Ac 20° C temperature
(3) End of larval rearing : 45 day old larvae
End of nursery stage : 90 - 120 day old (0.5 - 2 g of individual weight)
(4) Undervaluated - Normally twice the amount can be kept
(5) Separated cycles for larval rearing tanks
Eventual superposition of two cycles for nursery tanks
Figure 1 : Example of a five cycle production programme for a marine hatchery operating with sea-bream, sea-bass and shrimp
(Total shrimp cycle is about 30-50 days). The last cycle (V) is obtained through staggered spawning. Periods between
broken lines : superposition of two cycles for the nursery stage.
CONTENTS
1. Site choice
1.1
Socio-economic aspects
1.2
Water supply and water quality
1.3
Building permissions and eventual restrictions
1.4
Proximity of raw materials, labour supply and basic networks
1.5
Proximity of the place of destination for fingerlings Environmental factors
1.6
Environmental factors
1.7
Eventual existence of economic or social facilities
2. Production programmes
3. Dimensioning of a hatchery
3.1
Breeding and spawning unit
3.2
Phyto-zooplanKton unit
3.3
Larval rearing and nursery tanks
FISH HATCHERIES
STRUCTURES – EQUIPMENT - ECONOMICAL ASPECTS
Mr. G. BRUNEL
1. INTRODUCTION
The design of the hatcheries implemented :
–
The detail knowledge of the rearing techniques
–
The characteristics of the rearing site
–
The objective of production and/or of profitability.
In an economic context, there exists a compromise with this design phase
between the technical and economical parameters.
2. DESIGN OF THE REARING STRUCTURE
This entails a succession of stages, From general to particular, which define the
technico-economical functions and objectives.
2.1 Definition of the basic units for a hatchery
2.1.1. Definition of the three principle criteria of determination
–
Homogeneity in functioning
–
Identification of the environmental factors
–
Unity in management.
Let us define the following units (Each unit will have its own functional
characteristics which will permit the detailed definition of its structure.
Sea-bass - Gilthead sea-bream
1) Stocking of breeders/spawning
2) Phyto/zooplankton unit
3) Larval rearing/first fattening
4) Technical unit (workshop, machine room, boiler room, pumping unit)
5) Operation unit ( laboratory, administration, storages)
2.1.2. Secondary design criteria
–
Operation standards – Repartition of risks
– Standardization of productions
–
Possibilities of extension
–
Reports between the units
Ex.: Breeders/spawning – Larval rearing
Phyto/zooplankton – Larval rearing
Technical buildings – Biological units.
2.2. The structure of the units for a hatchery
They are defined, when the site has be chosen, according to the following data :
–
Environmental parameters of the site,
–
Environmental parameters of the basic units,
–
Technical constraints,
–
Operational and security constraints,
–
Sanitary constraints.
2.2.1. Breeding/spawning unit
This unit generally comprises three parts :
a) The natural maturation tanks
No particular structure is required here, as the environmental parameters are
similar to those found in a natural environment. However, so as to facilitate the
management of the tanks, and because, in these tanks, there is a much more confined
environment than in an open environment, it is advisable tO schedule a flexible covering,
similar to that used in agriculture, which will have the role of :
–
limiting the evaporation of the calories in Winter,
–
limiting the algae growth and ensuring shelter from the sun in Summer
–
limiting the variations in the salinity during heavy rainfalIs.
b) The staggered maturation tanks
These tanks which undergo different photo-period and thermic rhythms than
those of a natural cycle, must obligatory have a covering which will allow no day light
filtration to pass through and which will ensure good maintenance of the
environmental conditions.
The type of structure will depend on the site chosen and on the economic
context, and can range from a double wall greenhouse having an opaque lining in warm
temperate regions, to the industrial type building, with eventually air conditioning/heating.
c) The spawning tanks
This tank is employed indifferently for breeders which mature in natural
conditions or in controlled conditions. It is thus confined to the most restrained
conditions, in other words it has not the same kind of structure as the tank employed for
staggered maturation.
All these tanks, which have generally a capacity of more than 20 m3, can be built
according to many different procedures. The choice will depend on the context in the
country in question. The moulded reinforced concrete tanks, circular in shape, are the
most advantageous in many cases.
2.2.2. Phyto/zooplankton unit
This unit is comprised of two rooms :
–
The phyto-plankton room, which requires a regular temperature of 22°C.
–
The zoo-plankton room (Rotifer, Artemia) which must ensure a temperature
of around 20-28° C.
These two rooms are closely connected to one another, as most of the algae
produced are distributed to the rotifer rearings. The choice of the structures will here
again depend on the prices.
The phyto-plankton culture rooms are well known and have been described
many times, by different authors. Therefore, we shall not enlarge on this subject. A more
simple alternative, less expensive but also less efficient, is that the bloom be cultured in
a semi-controlled environment. This solution can not be justified but in countries which
do not have great drops in temperatures in Winter. They permit important economical
realizations.
The rotifer room is equipped more often with polyester containers of cylinderconical shape (1 to 2 m3) which are thermo-regulated. The temperature of the water
having to be at around 26° C, special attention will be taken for the insulation of these
containers, especially the upper parts. If this point is properly controlled, the rotifer
culture containers can be placed in a low costing structure (agricultural green house).
The Artemia room is divided into 3 parts :
– The decapsulation zone, having three tanks, one for hydration, one for
treatment and a final one for rincing.
–
A set of polyester incubators.
– A set of fattening tanks (2 to 4 m3 ) of Foster-Lucas type which can be built in
reinforced concrete and have a polyester covering.
The two last sets are thermo-regulated (26 to 28° C) and must be perfectly
insulated (idem rotifers).
2.2.3. Larval rearing and first fattening units
Generally, this unit is divided up into three parts (larval rearing, first fattening,
recycling circuit,) constituting a rearing module. .
a) Larval rearing tanks
– The shape, dimension, construction method and operating principles vary a
lot depending on the hatchery.
– The shape : circular, subsquare, raceways cylinder-conical : this latter shape
is the most renown at the present.
– The dimension : from 1 m3 to 45 m3. Today, there is a marked tendency to
limit the use of big tanks in favour of smaller tanks.
– The construction method : reinforced concrete polyester, polyethylene,
plywood with a PVC canvas covering. polyester is being employed more and more
today.
– The operation principle : this can range from very intensive (more than 150
eggs/liter) to extensive type (10 eggs/liter). Densities of 100 eggs/liter is the amount
most often employed.
As far as we are concerned, we employ cylinder-conical polyester containers of 1
to 3 m3, which is a good compromise, ensuring a good physico-chemical regulator in the
rearing tanks.
The larval rearing is carried out while employing the initial densities of around
100 eggs/liter.
b) First fattening tanks
They permit fry rearing from the beginning of its metamorphosis until it reaches
an average size of 1 to 2 g. In practice, from the 45th day onwards, the sea-bass fry is
transferred from the larval rearing to the fattening tank (60 to 65 days for the gilthead
sea-bream).
The rearing, from this moment, concerns trout rearing and the structures are
much similar to those defined for these species (raceways, circular or sub-square tanks.
Polyester is frequently employed along with reinforced concrete, with or without a
polyester covering.
c) Recycling circuit
Recycling has as objective the limitation of energy consumption so as to maintain
the temperature in the rearing environment and it combines the following elements :
–
Waste water recovery canals,
–
Detritus chambers (excreta trap, plate detritus chamber),
–
Scumming system,
–
Pumping station,
–
Regulated heat exchanger,
–
Biofilter having a polyester fluidized bottom,
–
U.V. Sterilization (for the larval rearing).
These rearing units can be sheltered depending on the climate, under green
houses or in industrial type hangars.
2.2.4. The technical building
The technical building is a unit which must be separated from the other facilities
and sheltered in an industrial hangars.
It is separated from the other structures for the following reasons :
–
Technical : better conservation of the material located outside the rearing
structures, the air of which is vapor-saturated. Indeed, the costly material is
often prone to corrosion due to humidity, and sea-air.
–
Environmental : Indeed, the noise and vibration caused by the machines can
have a negative affect on the rearing.
–
Management : As the personnel who intervene in this unit are specific
(maintenance personnel) for sanitary reasons, access to the rearing zones is
thus restricted to only the personnel concerned.
This building is generally divided up into the following compartments :
–
a "hatchery" pumping station along with a set of filters (one compartment)
–
an air-blower station
–
a water heating/cooling system
–
a electricity compartment divided into two distinct sections, which are the
transformer and the emergency power-unit in one section and the general low
voltage cupboard in the other section.
Remark : There exist many different heating/cooling production sources. For the fish in
the Mediterranean, calories are more in demand than cooling methods. A mixed system
is therefore generally employed which includes :
–
a principal source of heat, which can either be a fuel heater or a thermal drive
- in situ combustion (geothermics)
–
an adjustable heating/cooling source which is the heat pump.
3. THE EQUIPMENT
3.1- Generalities
The choice and selection of the equipment is of prime importance in the concept
of a hatchery, as it is necessary :
– to answer the necessary requirements in the defined conditions, through the
construction work studies; for example, the electric motors must be perfectly insulated
against humidity and the existing temperatures.
– to minimize the operation costs of these devices : this always calls for an
arrangement between the purchase price (investment) and operation cost.
– to examine the maintenance problems which are always of importance as the
work is carried out in humid environments, with high temperatures in a marine
athmosphere.
– to schedule the stand-by equipment; the principal devices (pumps, aerators .
...) will be scheduled on the double. Great attention must be paid to the choice of the
material which should have a slightly superior capacity than required (overestimation of
security).
– to schedule spare parts when purchasing the material thus enabling to
intervene when break-downs occur,
–
to choose material which will limit upkeep and maintenance requirements.
It is only through experience that the correct choice can be made.
The principal equipment required for a hatchery arc hydraulic, thermic and
electric devices.
3.2. Hydraulic equipment
a) Pumps : Generally, they have feeble or average flow discharges, and a
pressure permitting to combat the different head losses of the circuit (canalizations,
connectors, filtration system... ). Sumerged or surface centrifugal pumps will be chosen.
The material should not be corrodible by sea-water and should be non-toxic to the
animals. Generally, Ni-Resist iron should be employed (iron/nickel alloy). However,
corrosion by the sand can not be avoided (mechanical corrosion) and thus a stock of
spare parts for all the mobile parts of the pumps must be scheduled.
Remark : It must be ensured, that all the hydraulic circuits, can be disassembled,
separatly, so that when they require repair, cleaning or desinfection while employing
toxic products, one is free to do so easily.
(b) Filters : Swimming pool stable standard polyester filters are mostly employed,
due to corrosion problems in sea-water. However, with the use of polyester, a pressure
problem arises (at present, we are practically limited to 3 bars).
Remark : All the sea-water pipes are made in PVC plastic of natural flow or pressure
flow type.
c) Aeration : Two types of device can be employed ; either the compressor,
requiring a compressed air reservoir or blow tank storage or preferably, the superblower
ensuring a feeble pressure but a great flow which requires to be permanently in
operation (no storage).
3.3. The thermic equipment
a) The heating systems
They ensure the heating cooling requirements. The heat pump will suffice if the
needs are well balanced. There exist many solutions for the heating system :
–
the fuel heater,
–
the geothermic recovery (+ heat pump),
–
the electric heater (resistor)
–
the industrial recovery of calories.
The material is selected depending on the price, in Kw/h and in fuel, which varies
depending on the country. The feeble energies alone do not suffice for the hatchery
tanks. they are generally associated with the others so as to limit the running costs.
b) The exchangers
This is the meeting point between warm and fresh water, generally flowing from
the heating systems (boiler, heat-pump, drilling, ... ), and the sea water flowing from the
rearing. For reasons of corrosion and toxicity, titanium plated exchangers are currently
being used at present. They resist well to marine corrosion and have a remarkable
thermic performance .
3.4. The electric equipment
They include emergency power units, switch cupboard, along with the control
equipment. This is relatively current equipment. Let us pay special attention to the
insulation and water tightness of these cupboards.
4. ECONOMIC ASPECTS
4.1. Investments
The construction costs of a hatchery depend on the site, the rearing technology
chosen and the compromise between the technical considerations on one hand and
economic on the other (relation between investment cost and running cost).
As an example, for a sea-bass/gilthead sea-bream hatchery, with a capacity of 1
million fry of 1 to 2 g/year, the repartition of the investments takes place as shown here
following (Economic conditions, France 1985) (Total amount : 8,5 million F.F.).
Sea-bass — Gilthead sea-bream
Annual capacity
1 million of sea-bass fry
100 000 gilthead sea-bream fry
Total amount of investment
8,5 million francs (France 1985)
Framework/Civil engineering
30 %
Hydraulic - Thermic - Aeraulics
35 %
Diverse equipment (green houses, containers,
tanks, laboratory)
13 %
General electricity
10 %
Studies/Supervision of the works
12 %
4.2. Running costs
In the case of the fish hatchery seen here above (1 million sea-bass Fry and 100
000 gilthead sea-bream Fry) the cost price of the fry entails the following elements, in a
routine year, in other words from the 4th year onwards :
+
Personnel expenses
+
Energy
37,5 %
9,0 %
+
Specific purchases (Artemia, plankton, diverse )
8,9 %
+
Technical assistance
8.0 %
+
General upkeep
5,0 %
+
Other diverse expenses
5,8 %
+
Amortization
+
Financial expenses
20,0 %
5,6 %
Total
100,0 %
This repartition of the cost prices leads to the following comments :
a) The hatchery entails and will continue to do so, for a long time a high
technological activity which requires qualified personnel. The personnel and technical
assistance represents 45,5 % of the cost price of the fry (which is nearly half). An effort
for automatization must be undertaken so as to limit this important cost price factor; we
shall also try and reduce certain tasks such as feeding (in avoiding live food, for
example).
b) The energy costs are low (9.0 %). Thus any technological efforts made here
will not give a noticeable improvment on the production cost. The choice or the designer
must concern moreover the reliability of the material rather than the economy of energy.
c) The amortization is high (20 %). Consequently, it is necessary to find less
expensive construction technologies which will be less sophiscated.
CONTENTS
1. INTRODUCTION
2. DESIGN OF THE REARING STRUCTURE
2.1. Definition of the basic units for a hatchery
2.1.1
Definition of the three principle criteria of determination
2.1.2
Secondary design criteria
2.2. The. structure of the units for a hatchery
2.2.1
Breeding/spawning unit
2.2.2
Phyto/zooplankton unit
2.2.3
Larval rearing and first fattening units
2.2.4
The technical building
3. THE EQUIPMENT
3.1 Generalities
3.2 Hydraulic equipment
3.3 Thermic equipment
3.4 Electric equipment
4. ECONOMIC ASPECTS
4.1 Investments
4.2 Running costs
THE CONCEPTION OF "INTENSIVE TYPE" FISH REARING FACILITIES
WITH PARTIAL OR TOTAL WATER REGENERATION
Mr. J. PETIT
1.
2.
Rearing volume
1.1
Limit design
1.2
Conception of the structures -an example-
Water supply flows
2.1
Limit design of the hydraulic network system
2.2
Limit design of the water treatment system
PREFACTORY NOTE
The lecturer has no experience in marine hatcheries. The method exposed here
deals with all the different types of intensive fishculture where the aquaculturist tries to
free himself of the incidents of the environment (intensive). This applies to hatchery and
fry rearing of Salmonidae and species whose growth speed must be accelerated by
means of heat so as to reach economic profitability (eels).
Marine hatcheries are linked with this type of fishculture.
The description of the functions of the water and equipment which are necessary
for a marine hatchery were exposed at MOTTA DI LIVENZA (MEDRAP, TD/86/03). This
description permits the formulation of the contrat procedure for the building works of a
facility.
The calculation methods for the equipment have been exposed in TUNIS during
the engineering session organized by MEDRAP.
Let us propose here the examination of the relation between the technical
choices and investment cost, which will be a guide for the conceiver. The analysis of the
operating costs and gains linked with each type of structure remains to be elaborated.
INTRODUCTION
The investment cost will closely depend on the choices taken concerning the
rearing structures (tanks) and the water supplies (open circuit or recycled water).
The rearing VOLUME depends oh the maximum stock of fish maintained during
the cycle, which will thus require a management study of the stocks from their growth
speed and dispersion.
The WATER SUPPLIES depend on the oxygen consumption and pollution
thresholds which the fish support.
Although it may be possible to minimize greatly the investment by means of
certain technical choices, the outcome of this, results generally in higher operating costs.
Thus the use of pure oxygen permits to decrease the SUPPLY, and to make
important economies on the hydraulic network system and on the water treatment
system : on the other hand, this will also lead to a supplementary operating cost entailed
through the payment of gas
Likewise the heating of the water will increase growth and will also reduce the
volume of the tank necessary for a given production, but at the same time it will also
entail a supplementary cost in energy.
The rearing structure and supply flows having been defined, we can now
research one by one, the most efficient EQUIPMENT for oxygenation, purification,
thermoregulation when these can not be obtained from the natural environment.
1 . THE REARING VOLUME
1.1. Limit design
The rearing volume is defined by the zootechnical factors and by the organization
of purchases and sales. We shall refer ourselves to the modelization of production,
especially that of FAURE *.
* Seminary organized by GEDITS (Groupe d'Etude et de Diffusion de l'information Technique en Salmoniculture; on the
production of large trout (Oct. 1986).
For the same annual production, we can thus installate structures of very
different sizes.
The SIZE of the structure will be defined by :
–
The maximum stock during the year,
–
The rotation of the stock (time period spent by the fish in the structure)
The study of fishculture thus commences by the management study of the
stocks.
–
The MAXIMUM STOCK determining the rearing VOLUME depends on :
•
The planning of the fish inputs ; the more staggered they are in
time the greater the production will be for a same facility.
•
The growth variability : the more staggered their arrival at commer-size is
the better the production will be for a same stock.
•
The commercial size of the animals ; the bigger they are, the greater
the stock for a same production will be (especially when the cycles
overlap).
The maximum stock thus depends principally on the Biological factors and on the
purchase-sale planning.
- The ROTATION OF THE STOCK will define the DEPRECIATION of the
rearing structure. This rotation depends on the GROWTH SPEED, which can be
controlled by the temperature, the rotation of the stocks also depends on the animals
input and output sizes in the rearing.
It is with this notion of profitability for the rearing structure, the speed up of the
growth rate by means of heating, that brought about the use of of recycled waters in
rearing, so as to economize calories. The analysis of the project consists in balancing
the costs linked with recycling + heating, with the gain obtained by the greater growth
speed.
1.2. Conception of the structures : an exemple The possibility to obtain higher densities reduces the investment cost in tanks for
a given production.
The different tropisms can be negatively or positively employed to improve the
distribution of the animals in the rearing volume : food, oxygen, lighting.
The most spectacular results are obtained with fish which normally stay at the
"bottom" such as the brown trout , salmon, eel, silurius, catfish.
Indeed, when a good distribution of the animals in the tank is obtained, it permits
limiting competition with regards to the water, oxygen, food, lighting, a more
homogenous growth rate and "better" animals (agressivity). We can still improve on the
results, in separating certain parts of the tank : food, habitat, etc...
We shall find here under a skeleton diagram furnished by P. MAUREL and
employed by an eel rearing specialist.
With eels, it was known that in offering the animals supports (grils, tubes), the
density could be greatly increased (up to 150 kg/m3 ).
The disadvantage of those supports is that they are priviliged zones for fouling
and the development of algae and fibrous fungui.
Such a structure is only possible if the water is kept completely clear by means of
intense water treatment, of the food distribution zone which is separated from the habitat
zone and the rapid collection of fresh mud.
The cost of the installation of the tank will be balanced with the improvement of
the water quality, the reduction in the main purification system and the increase in
density.
DIAGRAM OF AN EEL TANK BY P. MAUREL (1)
(1) AQUINOXE, 8 rue d'Ouessant, B. P. 40 - 35760 - St. GREGOIRE - FRANCE
•
The habitat zone is installated in accordance with the dominating tropisms
of each species ; support (eel), light (silurus). It is well oxygenated by the recycled
supply flow of water.
•
The feeding zone is supplied with water which is not recycled during
feeding. The food matter will therefore not contaminate the recycling.
•
The decantation zone receives no water renewal, the tropisms for the
oxygen and the currents keeps the fish in the habitat zone. The mud extracted is dense
(feeble time stay, no mechanical mixing, mud and facces only, which the animal do not
put back into suspension).
•
Advantage : The clarified water permits sanitary treatments and rapid
water flows over the filter.
•
No decantation required
•
Disadvantage : Supplementary tank costs.
2. WATER SUPPLY FLOWS
The defining of the rearing volume involves zootechnical and commercial factors
which will be seen here below.
The remaining infrastructures for the fish culture are linked with the HYDRAULIC
network and WATER TREATMENT systems, oxygenation, heating, purification.
Their definition entails the choice and calculation of :
– The dimension of each structure (the bigger it is the more expensive it will be)
which will depend on the supply flows.
–
The power of each device :
Quantity of oxygen required, quantity of polluants to be eliminated, type of
pathogenic germs to be destroyed. These will vary according to the species and
category of the animals.
– The type of machinery to choose : surface aerator or deep well type, gas or
fuel heating, etc... for which the choice will depend on their efficiency, and local criteria,
for example availability.
2.1. Limit design of the hydraulic network system
It is defined by the supply flow
in reducing the supply flow by means of certain technical devices, we
considerably reduce the cost of the facility.
The supply flow can have different functions :
–
Oxygen supply
–
Evacuation of waste matter
–
Supply of calories or negative kilocalories
–
Food supply (bivalve rearing)
The impact of the supply flow on investment being important, it is advisable to
study solutions of substitution or cost reductions for the functions which concern the
supply :
–
The water flow can be thus reduced with regards to oxygen requiremenent :
•
by staggering, the feeding periods
•
by increasing the oxygen tenor input :
Use of pure oxygen (see example here under)
–
The supply flow can be reduced as to concern the purification needs :
•
By organizing the tanks {see below)
•
By purifying the water in the tank : BIOMACO system (See report of Mr.
PETIT - MEDRAP Session on engineering - TUNIS) .
•
By use of a highly digestable food.
– The caloric or negative kilocalorie requirements can be reduced by means of
insulation (covered).
AN EXAMPLE OF HOW TO REDUCE IN SIZE THE HYDRAULIC NETWORK
SYSTEM WITH REGARDS TO THE OXYGEN
WHERE – Q = the supply flow
–
∆ O2 = the concentration of oxygen in the water taken away from the
threshold tolerated by the species;
–
TE = water treatment (oxygenation, purification)
–
CO = Oxygenation capacity to be furnished to the tank.
A given oxygen supply, can be obtained by different means. The choice of the
supply flow is determinant for the investment, the choice of the O2, concentration is
determinant for the operating costs.
Thus in the example given here below, the required supply permits from 2.25 m3
/H à11,5 m3 /H for a same stock.
NUMERIC EXAMPLE
HYPOTHESIS – Oxygenation of the tanks for 100 kg of animals, which means 25
g/H of dissolved oxygen must be furnished.
– 25° C temperature (saturation : 8 mg/l)
– Oxygen threshold in the tank : 5 mg/l
– Presence of a biological filter, which requires 20 g/H of oxygen.
•
A supply flow with a aeration system which recovers the water at 90 % of
saturation
•
A supply flow having an aeration system before passing through the filter and
a second before passing into the tanks.
•
A supply flow with an oxygenator (oxygen paid for) furnishes water at 25
ppm.
2.2. Limit design of the water treatment systems
The supply flow systems consists in :
–
A supply flow of water from the exterior
–
A recycled supply flow.
Both of these supply water flows can represent all or part of the water flowing into
the tanks.
•
The supply water flow can, when of good quality, ensure all the functions
devolving to water in fishculture.
In numerous cases the procurement of a water supply flow from the exterior is
rather cheap : gravitional water intake, form a river and by the use of tides.
•
The recirculation of the water reduces its qualities which necessi-tates one or
more water treatments.
•
Recycled flow
To maintain 10 g/m3 of SM at average value in the tanks, a minimum flow is
necessary :
Qp x 10 g/m3
=
Pollution eliminated by the new
water
Which is Qp = 2.5 m3 /H
Pollution engendered by the
fish
A new water flow of 2.5 m3 /H implies that the water contains no SM at tank inlet
level. Thus this is either new water, or water obtained from a filter with a 100 % output.
Such a filter, if feasible, would be very expensive.
Thus we shall test flows of more than 2.5 m3 /H and calculate the out-puts with
the formula stated here above, while employing the value of the example, which is :
W = 25 g/H
Qo = 0.1 m3 /H
C = 10 g/m3
Recycled flow m3 /H
Output necessary for the
decanter
Surface area of the decanter
m2
3
5
10
80 %
50 %
25 %
3.7
2.5
2.5
The surface of the decanter is given for a sediment coefficient of (2). (See report
by J. PETIT/MEDRAP session on Engineering)
We remark that :
– It is not the smallest flow which permits the greatest economy on the
decanter.
When one must recycle water due to a insufficiency in the quality or the qunatity
of the supply, two types of questions can be asked :
–
How much of the water supply is it necessary to conserve ?
– Which devices are necessary so as to satisfy the requirements in oxygen,
heating, etc... of the rearing ?
ELIMINATION OF POLLUANTS
The water supplied will carry the waste matter out of the rearing.
The quantity eliminated is the product of the supply flow by the concentration in
the tank.
The more exact one is about the quality of the water the greater the supply water
flow will be, and if insufficient one should demand filters (elimination of the ammonia,
and of the organic matter in suspension).
To study the effect of the choices on the investment that one can make, it is
recommended to use the following formula ;
– R is the purification efficiency necessary so as to obtain C concentration in
the tank (g/m3 ) with a new water supply Qo (m3 /H),
with a recycled water supply Qp (m3 /H),
and a polluant discharge W (g/H).
– The higher R is the more expensive the device with equal discharge flow will
be, for a given device (decanter .filter, sterilizer), it is easy to follow the evolution of the
costs depending on the thresholds and flows chosen.
EXAMPLE
HYPOTHESIS – 100 kg of animals
fed at 2 % with a dry pellet food
-
–
Objective : 10 g/m3 max de matter in suspension
–
Load : 50 Kg/m3, and no decantation possible in the tank
–
Feeding at 2 % which gives 300 g of SM per Kg of food (this
corresponds to a transforrmation index of 1.5 - 1.6)
–
m3/H of new water at disposal.
above a certain flow there is no more gain in the structures surface area
although the admittible output is less.
We can thus study the investment and operation cost engendered by a more or
less important input of new water for each problem studied :
–
Elimination of ammonia and SM
–
Elimination of pathogenic germs.
We propose here under an example so as to define the power necessary in relation to
water treatment.
This power, whether it be a oxygenator or a filter, will vary with the choice of the
minimum or maximum thresholds of the physico-chemical parameters concerned :
oxygen, ammonia, SM, etc...
OXYGEN REQUIREMENTS
The calculation of the oxygen requirements can be done with the use of diverse
modelizations (LIAO, SPARRE, etc... ). An evaluation can be obtained for a trout type
food, in considering that the oxygen/food consumed ratio has a value of 250 - 300 g of
oxygen per ton of food (280 g/T of food for trout).
The choice of the minimum oxygen thresholds to be maintained will determine
the power to furnish so as to dissolve the correct quantity of oxygen necessary for the
animals.
EXAMPLE
Hypothesis : –
–
Water input 2 m3 /H at 25° C (8 mg/102 max.)
100 Kg of fish fed at 2 % of their live weight per day, which is 2
Kg/d entailing an oxygen consumption of around 25 g/H.
Tolerated threshold in the tank
7 mg/1
5 mg/1
30 mg/1
Oxygen supplied by the water
1 g/H
6 g/H
10 g/H
Oxygen to be dissolved
24 g/H
19 g/H
15 g/H
Power per Kg of dissolved 02
8 Kw
2.7 Kw
1.6 Kw
Power required
200 w
50 w
27 v
Basis : – 1 Kg of dissolved oxygen per KwH at Omg/1 of oxygen (high speed
turbines, hydroprojectors) standard (0ppm - 20° C) .
–
Quantity of oxygen dissolved in water at C concentration
Cs, Maximum concentration in oxygen (saturation)
We then remark that the power required can vary by a factor of 7.5, when the
threshold maintained for the oxygen in the tank passes from 3 to 7 mg/l and this for a
same quantity of dissolved oxygen which is available for the fish.
CONCLUSION
The limit design of the different parts of a rearing and thus the cost, is greatly
influenced by the choice of certain parameters.
It is possible to obtain significant investment reductions by analyzing the different
situations one by one, an optimization between investment and operation costs must
then be carried out so as to define the "right choice".
USE OF THERMIC DISCHARGES
Mr. Paolo BRONZI
Aquaculture was derived from fishing techniques carried out in a confined natural
environment, where the techniques employed became more and more sophisticated.
At the beginning, fishing took place in a sheltered environment, like a reserve for
hunting where neither the control operations on the water quality nor the prophylaxis or
therapy methods against pathologies were nor carried out. It was simply a matter of
stocking up with young fish captured in open waters ; feed, if provided, was only natural
fodder, and the animals grew in mixed populations without size selections.
Such enterprises were necessarily connected to particular environmental
situations of favourable characteristics, such as restricted and hydrologically controlable
environments, where little work was required.
An increase of human intervention was soon remarked in the structuration of
environments and management, mainly for the administration food and the control of the
water flow.
Later on the growing demand of products, brough about a greater and greater
industrialization of the productive systems with a consequent release from the natural
situation and greater human presence.
The development of artificial reproduction methods has been fundamental, since
it provided fingerlings to breeding size, releasing the productive systems from fishing.
In this way, aquaculture becomes more industrialized, creating artificial
environments, with pumping systems and quality controls of the water, fingerling
productions, food formulation and with a more and more mass utilisation of technologies
and authomatisms in management operations.
However, we are still at an "agriculture" level, even though advanced, since
there's no possibility to control completely the production cycles, according to the
demand. These concern in fact thermic trends.
The temperature of the water is therefore one of the most important
environmental factors, because it controls the whole life of aquatic organisms that are
heterothertm, which means that they haven't a stable body temperature, but assume the
temperature of the water surrounding them.
The temperature relationships for fish may be summarized as seen in fig. 1,
where the outside line represents the extreme values of temperature that the fish can
tolerate. As all the other values of temperature (resistance, tolerance, etc... ) the upper
and lower lethal limits increase with the rise in the acclimatation temperature.
The second line represents the extreme values of temperature that the fish can
withstand indefinitely ; in the zone of tolerance the fish withstand different levels of stress
that can reduce their growth rate and food conversion efficiency.
The area where the reproduction is possible indicates the thermal values that
don't cause any stress.
Fig. Schematic temperature relation diagram for a fish.
(From WHEATON, 1977)
If we use oxygen consumption to measure the metabolism, standard and active,
we find that if the temperature increases, between a definite range, both metabolisms
will increase of course (Fig. 2).
Fig. 2. Active and Standard oxygen consumption curves for goldfish.
(From FRY and HART, 1946).
Standard consumption is the oxygen needed to maintain the basic metabolic
rate; the active oxygen comprises the standard rate plus that necessary for the activity in
general. The difference between active and standard consumption can be a measure of
the oxygen available to support the activity at any temperature (Fig. 3).
Fig. 3- Difference between active and standard oxygen consumption curves for goldfish
(From FRY and HART, 1946).
The direct influence of temperature on growth and on food consumption is of
great interest to the aquaculturist. Fig. 4 shows an example of the influence of
temperature on the growth rate of a fish. The growth rate increases as the temperature
increases until a determined value is reached (27.5° C in the example) then the growth
rate decreases.
Fig. 4. Growth rate of largemouth bass fry at different temperatures
(From STRAWN, 1961)
This means that there is an optimum temperature for the growth rate ; at higher
values, the growth rate decreases.
These considerations are useful if the food, as in nature, is taken ad libitum but
when we consider an aquaculture plant, we must take into account the combined effects
of temperature and food ratio.
Fig. 5 shows the data from BRETT on the effects that the amount of food has on
the relationship between the growth rate and temperature for sockeye salmon.
It can be remarked that :
–
the best growth is obtained with food in excess;
–
at any feeding level, there is an optimum temperature for growth ;
–
if the feeding level is reduced, the optimum temperature of growth decreases;
–
if the feeding level is reduced, the growth rate at all temperatures decreases;
–
there is no growth or loss of weight near the upper lethal temperature
Fig. 5. Effect that the amount of feed has on the relationship between the growth rate
and the temperature for sockeye salmon
(From BRETT et al., 1969)
But the aquaculturist is interested in the cost of the production and not
specifically in the growth rate.
Fig. 6 considers an efficiency curve imposed on the growth rate curves.
Gross conversion efficiency is calculated as :
From the following diagram, we can see that the gross conversion efficiency
ranges from 0 to 25 % and that the best results are obtained at 12° C (this level of
temperature is lower than the optimum temperature for the best growth, which is 14.5°
C) with a feeding level of about 4.5 % of the body weight per day, obtaining a specific
growth rate of 1 %/day.
Fig. 6. Gross efficiency of food conversion in relation to temperature and ratio (From
BRETT et al., 1969)
This means that for every species, two combinations of temperature and feeding
level exist, that produce either maximum gross efficiency of food conversion or
maximum growth.
In general the aquaculturist can vary the water temperature between the
optimum for growth and the optimum for conversion efficiency, depending on the
availability of feed or the need to speed growth.
But we can see that the growth obtainable at the temperature and ratio for the
best growth is quite similar to that obtainable at the temperature of the best: conversion
efficiency by increasing only the food ratio. The best condition therefore is to maintain
the temperature of the water at the value for the best conversion efficiency, and to vary
the food ratio in order to obtain the best economic result, taking into due account both
the cost of food and the cost of the management of the plant.
The possibility to control temperature parameters allows a further development in
the industrialization of aquaculture.
Aquaculture in a thermically controlled environment allows as a matter of fact not
only a growth-rate increase and a better conversion factor of the food, but, most of all, it
permits the control of rhythms and time in order to optimize the utilization coefficients of
the structure and of water supply and so the economic productivity of the plant.
Therefore, it is possible to employ in aquaculture the following management
criteria :
1) Culture Turnover :
This concerns the breeding of species which prefer either warm water or cold
water. This is possible in thermal aquaculture, mainly in fresh water, since at our latitude,
the ranges of optimal temperature for the growth of these two fish categories are
available.
2) Shift of productive cycles :
During the year, different production cycles may be started, beginning with
reproduced fingerlings up to commercial size fish.
This is possible due to water temperature which are available and suitable for the
whole year of breeding, and this involves a rotation use of the tanks with a consequent
optimization of the utilization coefficient for the water supply and the breeding
environments.
3) Dividing production :
This consists in only developing all the productive methods, those phases which
can benefit must from thermic control. This involves, for instance, the production of
intermediate stages, when they represent the highest production possible for the
available condition, leaving the fattening operations to conventional systems where costs
are lower. This creates the possibility of integrating different systems of production.
4) Coordination between demand and offer :
Thermal aquaculture permits production to commercial size outside the natural
season, when the market demand is high and the offer is low, and in this way, it allows
to obtain good selling prices.
The most important and characteristic of these management criteria, permitted
mainly by thermal aquaculture, is the shift of the Productive cycle.
To show the advantage obtained in this way, let us compare two different
hypothesis, the First in conventional conditions and the second in thermal aquaculture.
In the first hypothesis we use conventional management criteria, and we assume
that the final commercial size is to be obtained while starting with fingerlings kept in the
same breeding tank.
It is presumed that the first breeding cycle has been completed when the second
one starts (Fig. 7).
Fig. 7. Annual production: conventional aquaculture
In this case the annual production is:
where :
PFC = Final production (kg/year)
Q = Water supply (m/hr)
r = specific water requirements (dm/hr.kg)
SB max =Stocking biomass (kg)
In this case the hatchery, following the natural biological rhythms, must produce,
all at once, the entire fingerling requirement of the whole system, and is therefore used
only once a year.
In thermal aquaculture it has been supposed that the commercial size can be
reached in a shorter time, approximately 2/3 (two thirds) of conventional time.
As a matter of fact in this case the temperature trends allow breeding to take
place practically throughout the whole year, but with different rates of growth, according
to the temperature of the season ; the period of 8 months is a mean value for use in our
calculations.
Thanks to the possibility to control temperature, it is possible to shift the start of
each production cycle, producing the fingerlings required for every fattening period.
If we suppose a shift of 4 months between fattening cycles, and by taking the
quantity of water supply that limits the maximum biomass possible in the system at any
time as constant, the biomass is obtained by adding animals of different size present in
the system at any given time (Fig. 8).
Fig. 8. Annual production : thermal aquaculture
The production of each breeding cycle PA is therefore less than SB max, since :
SB max = PA + PB
Where: PB is the biomass of the shifted growing population at the moment when the
cycle PA is harvested.
Assuming from experimental data that :
PB = 25 % PA
we get :
SB max = PA + 25 % PA
SB max = 1.25 PA
However, since the annual production in the Case of n cycles is equal to n times
the production of the cycle PA, i.e. :
PFT = n PA
we get
In the example, n = 3, so:
Deriving from this, the ratio between the annual production in both these cases
here, we can obtain :
from which :
PFT = 2.4. PFC
If n increases further, the annual production increases too, and as a result the
utilization coefficient of the structures also increases.
The increases, however, steadily decline, whereas the cost of starting a new
cycle can be taken as constant.
All this implies that there exists an optimum number of cycles per annum, the
exact definition of which will depend on the economic and managerial factors.
It is therefore clear that the possibility of shifting the production cycles offered by
thermal aquaculture, not only leaves the time needed to achieve commercial sizes, but
also has undoubted advantages in terms of production and management for both the
growing and reproduction structures,
In marine aquaculture, the time needed to reach commercial size takes normally
more than one year, and the previous considerations must be slightly modified.
If we remark the growth in different rearing conditions (Fig.11), we can observe
that in good thermal conditions, with warmed water, the first commercial size of 250 g
can be obtained in 14-15 months.
Intensive rearing in warmed recycled water (18 – 200 C)
Intensive rearing in natural waters (70 C during the Winter)
Extensive rearing in natural waters
Fig. 11. Comparison between the growth of sea-bass (Dicentrarchus labrax L) in
different rearing systems
(From RAVAGNAN, 1978)
Considering that in sea-water, the temperature of the water discharged by the
power station is also suitable for growth in the Winter period, and that the use of warmed
water in the hatchery makes it possible to accelerate the growth of the fry, and that
warmed waters during the year generally accelerate the growth of fish, it can be
assumed that commercial size is reached within one year.
In this Way, we can use year after year, the same tanks and hatchery.
If reproduction is carried out, we can obtain at the same age of life the situation
shown in Fig. 12.
Fig. 12. Growth and survival of Dicentrarchus labrax, up to one year.
The same situation is shown in fig. 13. where the "top" population reproduced
and selected for size early is comprised of the "heads" and compared to a mixed
population conventionally reproduced.
Fig. 13. Growth of population of Dicentrarchus labrax with different repro-duction periods
reared in a thermal fish farm.
Fig. 14 compares the trends of growth up to 500 g of a selected population,
reproduced early and reared in thermal aquaculture; en analogous population but
conventionally reproduced, and a population of conventional aquaculture.
It is also evident, in the case when the time needed to reach the final size is over
a year, that it is advantageous to shorten the time of Permanence of animals in the
tanks, particularly in thermal aquaculture, where the costs of building and management
are high.
Fig. 14. Growth of Dicentrarchus labrax up to 500 g in three different rearing conditions.
Thermal aquaculture is however economically feasible only when the energetic
resource is pratically free, since vast amounts of energy are needed to raise the
temperature of the huge volumes of water used, even if only by a few degrees.
If we consider for example, an artificial tank for fish rearing, characterized by
surface, depth, intake flow rate, its temperature will depend on an energetic balance
between the incoming and outgoing energies, which means that at every moment
equation (B) must be verified :
(B)
ES = Ein - Eout
where
ES = Stored energy
Ein = Incoming energy
Eout = Outgoing energy
Fig- 15 represents the most important energy fluxes to be considered :
where Ewi = energy of the "inflow water
Ewo = energy of the outflow water
Ei = energy of solar radiation
Ec = energy of convection
Ee = energy of evaporation
Er = energy radiated from water
Ea = energy reradiated by the atmosphere
Ebiol = energy used in biological processes
Echim = energy used in chemical processes
Elg = energy loss or gain from bottom.
Es, when exists, represented by the increment of the temperature of the water in
the tank, or by the decrement if negative.
Now, we can indicate, in a very simplified form, the expressions of various terms.
Es = h.S. .Cp.T
Ewi = Q.Cp.Ti
Ewo = Q.Cp.Tb
Ei = l.S. . ( l - r)
Ec = S.Ke. (Tb - Ta)
Ee = S.Ke.(Tb - Ta)
Er = S. . .T4. linearizing we can write
S. . .K*.(Tb - Ta)
and assuming for T* the Value of Ta and Kr = . . K*
= S.Kr.(Tb - Ta)
Ea = S. . . T6 in the same way :
= S. KA. (Tb - Ta).
If we suppose a steady state situation, which means the temperature of the water
in the tank doesn't change in respect to the time of day or season, and we want calculate
the energy balance in this situation with particularly known environmental situations, we
may use the following very simplified equation :
Q. Cp (Ti - Tb) + S.K - S. (Kc + Ke + Kr + Ka). (Tb - Ta) = 0
where ;
Q - flow rote (kg/sec)
Cp = specific heat of water (J/kg° C)
Ti = temperature of the incoming water : (° C)
Ta = temperature of the air (° C)
Tb = Temperature of the tank and of the flowing water supposing a perfect mixing
(° C)
l = intensity of solar radiation (watt/m2 )
S = surface of the tank (m2 )
h = depth (m)
= Stefan Boltzmann constant
Ke = evaporative heat exchange coefficient (watt/m2. ° C)
Kc = convective heat exchnage coefficient (from water to the air) (watt/m2. ° C)
Ka = idem (from air to the water) (watt/m2 . ° C)
= density of the water (kg/m3 )
Kr = reflection coefficient of the water
This equation can be utilized in many different ways :
1)
to determine the temperature of the incoming water (Ti) in order to maintain
the temperature of the tank (Tb) at a desired value with an indicated value of the inflow
rate (Q)
2)
to determine the inflow rate (Q) necessary to maintain the temperature in
the tank (Tb) at a desired value having the water supply at temperature (Ti)
3)
to determine the temperature of the tank (Tb), in a steady state condition,
knowing the inflow rate (Q) and the temperature of the water supply (Ti)
All this is only obtainable if it is possible to know the values of the environmental
parameters and the values of the related coefficients (Kc ; Ke ; kr ; Ka).
This kind of calculation generally due to the complexity of the variables can be
only performed by the use of a computer. Just to give an example, we can consider the
question of point 1. In this case, we want to know Ti :
We can assume the following values of the variables as representative of a
possible situation at our latitude :
S = 1 000 m2
Q = 100 kg/sec
Ta = 15° C
Tb = 25°C
l = 100 watt/m2
K = Kc + Ke + Kr + Ka (at our climatoiogical conditions, normally, we can assume
a value ranging from 20 to 50 watt/m2 .° C, depending essentially on the wind speed and
relative humidity of the air ; on average, we can assume 30 watt/m2 0 C. )
Using the previous equation, we obtain :
Ti = 25.5° C.
In the same conditions, but with the temperature of the air = 0° C, we obtain :
Ti = 26.6° C.
The difference between the temperature of the incoming water and the
temperature in the tank is not very big, but nevertheless if the temperature of the water
supply, depending on the climatological situation, is about 15° C, to heat the water in the
tank, we must increase by more than 10° C, the temperature of all the water flowing into
the tank.
The heatpower necessary is :
P = Q.Cp.(Ti - Tn)
where
Tn = temperature of natural water
The energy requirement for one day is :
In our example, we need about 100 000 Kwh, and if we use an oil burner, we
need about 8 600 000 Kcal/day, and by the equation :
where PCI = calorific power of the fuel (for oil = 10 000 Kcal/kg
c = combustion efficiency (for burner = 0,7)
we need 1.23.104 kg/day of oil, with a very high cost.
From this is derived chat the cost to heat the water necessary for a fattening
aquaculture plant is very high, and not valid from the economical point of view. The use
of heated waters is possible only when this warm water is relativement free like heated
waters discharged from an industrial plant.
The waters discharged by the power stations, where a large amount of water is
used to cool the condensers is a typical example.
According to the second law of the thermodynamic, in the process of producing
electrical energy, not all the thermal energy obtained by combustion or by nuclear-type
reactions can be converted into mechanical and then electrical energy; in fact, a fraction
of it, variable according to transformation efficiency, is lost off in the environment in the
form of low-temperature thermal energy.
In a modern high-potential thermo-electric power palnt, the rated transformation
efficiency is such that about 5P % of the thermal energy entering the system is
discharged to the environment (Fig 16).
Fig. 16. Energy fluxes
In a power plant fed by fossil fuels, part of this energy is discharged directly into
the air through the facilities and smokestack, while most of it is released into the water
through the cooling system.
In a nuclear power plant, on the other hand, there are no smokestack losses, and
the losses in the facilities are minimal, so almost all the waste heat is discharged into
water through the cooling system.
The energy discharged to the condenser, in which the steam used in the turbine
to produce energy is condensated to liquid form is equal to about 1 700 Kcal/kw
produced in a nuclear power plant, and about 1 100 Kcal/kw in a conventional fuel oil or
cool power plant.
The cooling system most currently employed is the OPEN CYCLE TYPE, in
which water drawn from the sea or a river is used as the refrigerating fluid, and after
flowing through the condenser, is returned to the environment with a temperature
increase of 8 - 10° C.
According to the laws of thermodynamics, the lower the temperature of the
condensed steam is the greater the efficiency will be (relation between the electric
energy and the thermic energy used) and consequently the temperature of the cooling
water is lower at the outlet of the condenser.
In a modern oil fired power plant (each unit of 320 Mw), the heat discharged at
the condenser reaches about 1 100 Kcal per kw produced, which represents following
the above considerations, a flow rate of about 9 m3 /sec of cooling water for each unit
with an average increment of temperature of about 10° C. It is clear that an enormous
quantity of heated water is available.
Another cooling system, used for power plants located in areas where water is
not available in great quantities, is the CLOSED CYCLE TIPE. with wet cooling towers.
In this case the water coming from the condensers is sent to large size
evaporation towers and, after giving out heat to the atmosphere/ this is returned to the
condensers : water requirements are considerably reduced, since only losses through
evaporation and drain-off must be compensated.
The cooling water temperature inside the towers is higher than in OPEN-CYCLE
cooling, but in both cases significant quantities of thermal energy are made available.
The principal sectors for application of this discharged heat concern essentially
agriculture and aquaculture, where its low thermal level can be beneficially used in the
biological processes which operate at ambient temperature, and which can be made
more efficient by increasing the temperature in a controlled fashion.
When the operator's experience has been verified in the specific sector as well
as in other parameters, such as the socio-economic vocation of the area and the
receptive capacity of the market, another problem arising is that the aquaculturist and
the heat-production system will inevitably interfere with one another.
The principal criteria of interface of importance for the "producer" may be
summarized as follows :
–
quantity of heat necessary and reliability required
–
effect on the production of electrical energy
–
cost of deriving the heat and, possibly, the area necessary
–
possible effects on installation safety
–
compatibility of the application with legal restrictions.
The important criteria for the "user" may be the following :
–
thermal levels of the water and quality requirements
–
reliability of the thermal source and the need for additional sources
–
cost of deriving the heat and use of the system
–
restrictions on occupancy of the area.
The first two steps of the previous considerations concern the physico-chemical
characteristics of the water discharged by the power station. The main problems at this
point can be summarized as follows :
1. Fluctuating thermal values : The increment of heat caused by the cooling
system of the power station is not constant, but depends on the activity of the energy
production system. This, in turn, depends on the request of electricity by the users,
which varies during the day and the week. Furthermore, the power station increases the
temperature of natural water, that normally changes during the year.
In this way, we have water with a temperature fluctuating during the day and
during the year, normally in a cyclical way.
2. Extreme values : The temperature of the water may reach values not suitable
for the species in rearing, during the Winter, if the power station works at low level or is
stopped (Christmas holiday, for example), and during the Summer when natural waters
already reach high temperatures.
These values can be lethal, and unsuitable for the growth or the health of fish.
3. Cold shock : If, in a very cold climate, the power stations suddenly stop, the
animals can be exposed to a cold shock, that can be lethal or very harmful.
4. Use of biocides against fouling: In order to ensure correct exploitation of the
plant, periodically blocides are used to kill the organisms that, clinging to submerged
surfaces, can clog tubes and other mechanisms. This is true especially in cooled seawater power plants, where normally chlorine is used.
5. Pollution of natural waters : pollutions of various quality can be present or
occur in natural waters before the power plant use them, and then the water passed
through the condenser can be polluted before the power station can have an affect on it.
Generally all these situations are not critical for fish in fattening ; however, some
security devices could be scheduled . For example, a reservoir can be useful in limiting
the drop in temperature and in avoiding acute pollution in poor conditions.
Elevated temperature can be avoided by mixing or substituting the waters
discharged by the power station with natural ones, and in this way, it is generally
possible to maintain the desired temperature in the breeding tanks.
When the above mentioned has been taken into account and it has been verified
that the risks are limited, the rearing can be carried out also directly in the discharg canal
of the power station, by means of floating cages.
The cages have many clear advantages; they do not interfere with the normal
operations of the power station ; the building costs can be very low, and cages are
installated rapidly.
However, serious problems may occur : it is not possible to control the water
characteristics, obviously ; fish disease can be normally controlled only by oral
treatment; fish feeding is not reguler and depends on the possibility of having access to
the cages (this is true, for example, in our situation, where the Po river during the floods
doesn't allow us to reach the cages) ; fish-handling and transfer are difficult and stress
occurs frequently.
In the hatcheries, where there is not a great requirement of water, and where a
good control of the physical and chemical characteristics of the water is necessary, the
control of the temperature of the water by means of an external energy supply is
required.
In this case, it is advisable to use a heating system with higher efficiency in
respect to conventional systems. This can be reached adopting a closed cycle system
for the recirculation of the water supply, this allows to reduce the outgoing flow rate to a
minimum, but requires the control of the chemical and biological characteristics of the
water, and the use of a heat-pump system which will permit to reduce the costs of
energy supply.
The heat pump is a machine whose principal purpose is to supply heat at an
elevated temperature, and it is identical in his principle to the refrigerator. The heat pump
allows to transfer heat from a low thermic level to higher one.
Fig. 17 represents the cycle of the heat pump :
1. A working fluid (vapour, freon ammonia) is compressed isoentropically from
low pressure and temperature to high pressure and temperature ; the working energy
(w) is acquired by the fluid ;
2. The fluid is condensed in the condenser at constant pressure, and transfers
the thermic energy (Q 2) ;
3. The fluid is then expanded isoentropically to its original pressure, and the
temperature decreases ;
4. The fluid is finally evaporated at constant pressure absorbing the energy (Q
1) in the evaporator ;
1
2
3
4
5
Compressor
condenser
expansion valve
Evaporator
Heat absorbed at low
temperature
6 Compression energy
7 Heat transferred to high
temperature
Fig. 17 – Heat-pump cycle
The thermal energy transferred in the condenser is represented by :
Q2=Q1+W
and the fluid at the end of the cycle contains the same energy.
The work W of the compressor relates to the difference of the pressure P 1 and P
2, and then of the temperature T 1 of the source from where the energy is absorbed and
T 2 to where it is transferred.
The performance of a heat pump is usually expressed by a "coefficient of
performance" named COP, defined as :
This means the ratio of the useful heat given to the hot fluid (Q 2) and the
amount of work (W) necessary to do it.
The practical values of COP range from 2.5 to 4, this means that the calories
obtained with the heat—pump are from 2.5 to 4 times greater than those obtainables by
an electric heater of the same power.
Fig. 18 represents a shematic plan of an application of the heat-pump
Fig. 18. Schematic representation of a heat-pump utilization
The warm water discharged by a power station can be used both in agriculture
and in aquaculture. Studies on the optimization of the use of this water in both these
fields have been carried out by several countries, listed in Fig. 19 - 20 -21.
A study has been conducted to evaluate the dimensioning of a project utilizing in
a correct way the entire effluent of a medium size power plant.
Let us consider a power station with 4 units of 320 MWe each, utilizing about 40
m3 /sec. of cooled water, located in the centre of Italy, using the water from the Po river.
Let us utilize half of the oxygen consumption to determine the ratio
biomass/water supply, and in supposing that we produce three different species (eel,
catfish and carp) ; for security reasons, only 70 % of the effluent of the power station is
used.
The project has scheduled fattening tanks ; a hatchery with a heat pump system
and first rearing tanks ; ponds to be utilized as reservoirs and as an additional cooling
system for these discharged waters ; appropriate facilities.
The total area occupied is 400 ha, 36 of which for intensive fattening tanks, and
360 for ponds. The final production is over 5 500 tons. Fig. 19-20.
Fig. 19. Energetic balance
Fig. 20. Ideal thermal fish farm utilizing warm water discharged by a power station
BIBLIOGRAPHY
HOAR, W.S. ; RANDALL, D.J. ; BRETT, J.R. 1979.
Fish Physiology. Vol. VIII. Bioenergetics and Growth. Academic Press.
ROGER, G.F. ; MATHEW, Y.R., 1965.
Engineering Thermodynamic Work and Heat transfer. Longmans.
WHEATON, F.W., 1977.
Aquaculture Engineering. John Wlley & Sons.
BRONZI, P ; PARRINI, F. 1984.
The management optimization of a thermal aquaculture plant. XV annual
ESNA Meeting. September, 3 - 8. PLACENZA.
PRODUCTION OF PHYTO AND ZOOPLANKTON
Mr. G. FANCIULLI
1. INTRODUCTION
In aquaculture, the production of live food for marine fish larvae, crustaceans and
molluscs, is certainly the first important point so as to ensure success.
Indeed, one of the first obstacles encountered during the first attempts of larval
rearing was the necessity of having at disposal live food, small in size, in great quantities
and so easily reared.
This was one of the major obstacles for the development of the different
techniques of induced reproduction.
In Japan during the sixties, so a relatively recent period, it was remarked by
chance that the use of Brachionus plicatilis was interesting as first food for marine fish
larvae.
Since then, this direction was followed and the results obtained succeeded in
bringing induced reproduction to industrial level. At present, it is now possible to select
between two rotifer stocks, small and big, which are distributed in turn.
It has also been possible to regulate the growth of the rotifer by intervening in the
food distributed to it.
2. THE PRODUCTION OF PHYTO AND ZOOPLANKTON
When the Japanese started using Brachionus plicatilis, the problem of rearing
great quantities had to be faced.
The method adopted and later on perfected was to rear Brachionus plicatilis in
big tanks. These tanks permittted having very similar conditions to those found in a
natural environment, and in eel fattening tanks where the development of rotifers had
been remarked.
The method consists in prevoking an algal bloom in big cement or plastic tanks
on which the rotifer may feed.
Briefly the method is as following :
1. The tank is filled with sea-water enriched with the traditional nutriments
(phosphates, nitrates, and eventually vitamins).
2. The phytoplankton chosen as food is inoculated (In Japan, Chlorella spp
is generally employed).
3. When the average cellular concentration is reached, the rotifers are
inoculated at a density of 15 to 30 ind/ml.
4. When the useful concentration is reached (150 to 200 ind/ml) a quarter of
the culture is taken every day or every second day as samples and
replaced by sea-water and phytoplankton.
This methodology, is the physiology and ecology of the rotifer is well known, is
easily applied and gives good results.
Around 15 years ago, when it was decided to take the First steps towards
industrial aquaculture, we tried to imitate the Japanese method. The results were only
average and probably due to the fact of the small amount of knowledge acquired in the
sector and also perhaps on account of the different ambiant conditions which had been
underestimated.
Both France and Italy decided upon the production of live food in smaller tanks
under cover . Thus a more sophiscated technology under strict control was adapted in
the aim of obtaining greater concentrations of limited space areas.
At first, the big production tanks of algae and rotifers were placed simply under
cover, thus vast surface areas were occupied. The surface area occupied by the
production of live food covered around 30 % of the rearing structures and so the
production costs were greatly increased.
Later on, and as to concern Italy, after 1980, there was an attempt made to
decrease the occupied surface area and to increase the productive capacity.
The use of yeast (inovation from Eastern Countries) as food for rotifers provoked
a decisive turn in this sector. This has been employed ever since.
Before stating the actual problems encountered and the technologies employed,
taken mostly from any own personnal experience, I should like to state briefly the
different phases around which the production of phytoplankton and rotifers evolve and
then to concentrate on mass production in average size volumes.
2.1. Production cycle of phytoplankton.
The algae most employed in aquaculture are, following the description given by
PARKER and DIXON, the diatoma : Phacodaectylum tricornutum, Skeletonoma
costatum, Cyclotella nana and Chaetoceros calcitrans, which are commonly used in the
larval rearing of peneidae.
Haptophycae : lsochrysis galbana, Pavlova lutheri which are both used in the
rearing of bivalvular molluscs and since their high content (in comparison to other
species) in long chain unsaturated fatty acids has been remarked.
The Prasinophycae : Platimonas suecica, is also used as food for rotifers,
together with Chlorophycae : Dunabiella, Chlorella and Nannochloris.
Culture phases
Figure (1) shows the successive culture phases of marine algae, carried out by
most aquaculturists. These different transfers, always from smaller to bigger volumes,
are carried out so as to reduce the time of culture and to divide up the production cycle
into different phases permitting at any moment a more efficient control. The principal
motivation behind these divisions is therefore to limit risks for the whole population.
The strain is the most important culture part of the whole cycle. The medium
employed is sterilized sea-water, enriched with nutrients, the normal quantity of which is
generally cut by half. The strains are. kept at a feeble light intensity and at a temperature
of 20 ± 1° C.
The erlenmeyer (Vol of ± 400 ml) is employed as intermediary transit volume in
the sole aim of increasing the culture volume.
This volume can be used at any time, and the culture can be kept in it for 4 to 5
months. The volume employed after this is a two liter balloon which is the fundamental
unit for the routine replications.
The following diagram shows the work methodology employed from B2 onwards
(Figure 2).
When full production is reached, the B2 is the minimum volume in which the work
can be carried out. Diagram shows that in the daily practice of a B2. one can obtain, by
simple dillution, a new B2 and, at least, 2 B6 (depending on the concentration, it is
possible to vary this relation), THe B6 can be either employed to inoculate bigger
volumes (bags) or so as to obtain intermediary cultures of rotifers. The use of the
pyrexglass balloons will eventually become outdated and will be substituated by the use
of the more economic and easily managed PVC bags enriched, with nutrients and then
placed in a deep Freezer.
When required they are filled with sea-water and inoculated. This practice is at
present being present and could permit to speed up the procedure.
Since yeast has been employed, we can consider that the 25 to 30 bag is the
biggest volume employed for unicellular algae cultures. Up to a few years back, the
production volumes of phytoplankton were on the contrary tank of several m3. As already
stated above, big volumes (more than 50 m3 ) for the culture of phyto-plankton and
rotifers are still being used in the Far East. Their great experience in larval and fry
rearing, together with the rapid development of this activity carried out on a large scale,
allow them to obtain satisfactory results.
2.2. Rotifer production
The species reared, is the Brachionus plicatilis, universally known and used in all
reproduction facilities. The studies carried out on this species, in the aim of improving
mass production, have covered many different spheres : The influence of the
concentration on the parthenogenetic reproduction, on the temperature and on the
quantity and quality of the phyto and salinity rates.
Likewise, the physiological aspects have been studied : the metabolic uniformity
concerning the changes in temperature and environment, the effects of the salinity and
pH rates on the consumption of oxygen and the osmotic regulation.
Finally, while still only imitating the Japanese, the studies have been directed
towards the ecological situations which occur in mass cultures.
Also of great importance, are the studies on the biochemical composition of
rotifers submitted to different diets. Indeed, it is clear, following the first results obtained,
that grave deficiencies can occur in certain compounds necessary for the development
of the larva. This is the case for essential fatty acids and especially long chain
unsaturated fatty acids (ac. eichosapentaenic, 20 : 5 w 3 and ac. dochosahexaenoic 22 :
6 w 3) which are vital for marine fish and which are practically absent in rotifers feeding
on yeast or certain algae.
This research brought us therefore to study the principal algal species used in
aquaculture so as to emphasize those containing fatty acids.
Like this, we remarked their total absence in Dunaliella and at a lesser degree in
Tetraselmis. While it appears that the highest percentage of unsaturated fatty acids is
found in Isochrysis galbana and Pavlova lutheri.
Another sphere of research wes developed with the perfectioning of a balanced,
inert diet, for rotifers and which could be used as an, intermediary therefore in relation to
the larva. At present, although a lot of progress has been made in this direction, we can
still not define its reliability nor efficiency.
2.2.1. Rearing method employed with Brachionus Plicatilis
The diagram shows more clearly than any explication could, how the operations,
concerning Brachionus plicatilis are carried out (Figure 3). The last tank, where "mass"
rearing takes place, can vary in size, from 0.5 m3 to 50 m3, depending on the
methodology employed. The method described here is that which schedules the use of a
tank of up to 1.5 m3.
Before giving details on the mass production the preceding phases shall be
briefly recalled.
The strain, like for phytoplankton, is the starting point of every cycle. A test tube
and erlenmeyer are employed, in other words volumes from 50 to 500 cc, but it is
possible to use only the erlenmeyer, especially during routine periods.
The 6 l balloon is for the intermediary culture which is capable of permitting the
"mass" production of rotifers, which in good feeding conditions reach greater
concentrations than 300 individuals/ml.
By diluting, we generally obtain 5 bags of 30 l, from a 6 l balloon, having a
concentration at the beginning of 10 ind/ml. These bags, containing algal cultures in
exponential growth phase, will be ready for use 5 - 7 days after the inoculation, when the
rotifers have reached a greater concentration than 200 ind/ml.
With the method here explained, the bags are used for "mass" production.
If greater dimensions are employed, it is probable that modifications in the
rearing method employed will be necessary.
2.2.2. Method employed for the "mass"production of Brachionus plicatilis in small
volumes
This point will be described in detail. As after many years of work in this sector, I
have remarked how difficult it was with neophytes to manage a series of volumes, on
parallel with the daily need of larvae for rotifers.
Therefore, I should like to try and give the most useful indications permitting
efficient management of this sector. Those who rear larvae, know that this objective will
be reached, if it is possible to supply a maximum amount of rotifers, which can be
produced daily and this throughout the whole larval rearing period.
The table gives details on the basic abiotic and biological parameters for the
management of a big volume :
–
filtered and preferably debacterized sea-water (UV lamp treatment)
–
temperature : 20 - 24° C
–
salinity : around 20 °/oo
–
aeration : 8 - 10 l/min
–
feeding : a) phytoplankton : 2 - 4 %/day of the culture volume in proportion to
the concentration of rotifers
b) yeast : till 50 ind/ml — 4 gr/million
from 50 to 100 2 gr/million
higher than 100 1 gr/million
The shape of the tank for this type of "advanced" rearing will be preferably of
cylindro-economical type (like those employed in larval rearing) as they enable
excrements and uneaten food to concentrate more easily. It is also useful to schedule a
"drain" in the bottom of the tanks so that the accumulated wastes can be eliminated
daily.
A study carried out over 3 years on the development of the different culture tanks
allowed me to focus, very approximatly, the average parameters where it is most
probable to obtain the regular development of a culture.
The graphs ( Figure 4) show the development over 3 years of 4 coefficients
employed so to estimate the growth of a population, compared with the concentration
(per ml) of rotifers when inoculated.
These coefficients are so following :
–
R : intrinsic rates of daily growth
This is a coefficient which expresses the capacity of a population to increase
exponentially,
–
TD : Time necessary for the population to double in number. Express
the time in days during which a population can double in number.
–
NT : Concentration of rotifers per ml when employed.
–
GG : average number of days of life in culture
These coefficients have been calculated for a total of 70 cultures during the
1981/82 season ; 148 during 1982/83 and 81 during 83/Feb. 84.
The averages obtained at diverse initial concentrations have been compared by
means of Tuskey test which permits to reunite them in the defined groups and to
establish a value scale (the test is significant) between the differences (if any exist).
These tests have permitted to show that the average value of the 4 coefficients,
obtained with an initial concnetration of 15 ind/ml is significantly superior to all the others
for the 3 seasons.
We can thus affirm with confidence that an initial concentration fluctuating
between 10 - 20 ind/ml is that which permits (in following the methodology explained
here above) to obtain a value R between 0.36 and 0.39, a time of reduplication varying
between 1.8 and 2 days, an average duration of the culture of 7 days and a final
concentration of between 175 and 215 ind/ml.
The some analysis carried out with tanks of double the capacity volume (1 200 l)
didn't give as constant results from one season to another. It may happen that at the
dimension aleatory factors could count as remarked with volumes of bigger dimension.
Another parameter studied during this period was the Ro value or fecundity
coefficient which is the relation between the total number of egqs counted in a sample
and the number of individuals. This value indicates more easily the reproduction capacity
of a population. The higher the coefficient, the better the linving conditions of this
population will be.
It appears from the results (as seen in the Fig. 5, that the 2nd and 3rd day after
the inoculation are those when the population present; the greatest amount of eggs and
confirms in this way (visibly) the correct development of the population.
Besides these more "matematical" coefficients, there exists other more empiric
parameters which permit to control the development of a culture and to schedule its
evolution. The use of yeast has permitted by its integration with the algal rythm to obtain
higher concentration of rotifers in the cultures. An excessive distribution can cause grave
pollution problems which can provoke in a few hours the total destruction of the culture
and consequently the difficulties arising from this easily be imagined at larval production
level.
The premonitory signs can be the apparition of a more or less thick layer of foam
on the surface, rich in proteins and the consequence of an increase of the ammonia
level, as well as the persisting typical odour of fermentation.
In this case, the culture water tends to become whitish and not transparent.
Therefore, it is better to use the culture immediately, empty the tank and filter the rotifers
before they are completely destroyed.
For this reason, in the table presented, I have indicated 3 different doses of
yeast, inversely in proportion to the increase of the rotifer concentration.
The data collected over 3 consecutive years of experience show a progressive
increase in the results obtained and the methodology employed is confirmed worth
while.
ROTIFERS PRODUCTION DURING 4 CULTURE SEASONS
Years
1
2
11.2
60.1
13.7
3
4
5
9 172.1
1 506
11
1980-81
162.3
1981-82
142. 5
9.9
81. 3
9.1
8 494.8
764
6
1982-83
212.7
25.7
125.0
12.5
19 445.8
1 209
9
1983-84
205.1
75.9
123.1
45.5
10 281.0
56O
9
1981-82
102.9
9.1
128.8
0.6
3 735.2
224
1982-83
132.1
25.9
225.0
6.8
4 505.0
157
2
2
In column. 1, the rotifer concentration per ml concerns the moment of use.
In column 2, the average production for each culture cycle (expressed in millions)
and in column 3 the global production for the whole season (expressed in millions). This
column must be read while comparing it to column 4 where the total number of days of
culture is expressed, in other words, the time during which the tanks were in operation.
The first tests carried out in 1980/81 while employing plat bottom tanks (creating
great problems due to the accumulation of wastes) gave the first good results.
During the 81-82 period, we have used conical-cylinder tanks of 600 l, and the
technique employed gave excellent results.
During the 82-83 and 83-84 periods, we have improved on the method employed
and so better results were obatined.
With this method, we were able to triple the rpoduction of rotifers when compared
to the period when we only used algae as food, and to reduce the surface area by, at
least, 50 %.
3. CONCLUSIONS
As already stated, there exists numerous rearing methods for phyto and
zooplankton, each valid, depending on the characteristics of the facilities and of the
environment where the work is carried out. One of these methods is that which I tried to
explain to you and which is adapted, in my opinion, to facilities located in cold climate
regions (possible having night frost and long period during which the temperature is
below 100- C.) and thus where it is necessary to work under shelter. In this situation, the
high cost of construction along with the difficulty (especially in Italy) of obtaining the right
for the construction of vast buildings, made us reduce as much as possible the space
reserved for rearing. This is why we have insisted on rearing live food at very high
concentrations.
And so as to obtain this goal, we had to perfect a technique and ensure constant
control.
CONTENTS
1.
INTRODUCTION
2.
THE PRODUCTION OF PHYTO AND ZOOPLANKTON
2.1.
Production cycle of phytoplankton
Culture phases
2.2.
Rotifer production
2.2.1. rearing method employed with Brachionus plicatilis
2.2.2. Method employed for the "mass" production
3.
CONCLUSIONS
Figure 1: Phytoplankton culture
Figure 2: Routine Cycle of Phytoplankton Culture
Figure 3 : Rotifer Culture
Figure 4: Evolution of 4 indexes over 3 years, permitting the estimation of growth of a
rotifer population.
Figure 5: Evolution of the fecundity index Rc
MICROORGANISMS USED IN AQUACULTURE
THE NATURAL ZOOPLANKTON YIELD
Mr. A. PONTICELLI
1. INTRODUCTION
The production of phytoplankton and zooplankton to feed marine species larvae
remains one of the most important obligations in the management of a modern hatchery.
The production of live food, which in passing, is very expensive, is always
obligatory due to the very poor results obtained with inert food up to present.
The failures, with the use of micro-particles are due especially to :
– the absence of movement; the larvae are attracted towards zooplankton as it
is continuously in motion.
–
Particles fall to the bottom rather quickly.
–
Consequently the tank becomes polluted more quickly.
To these points, let us not forget to add, that, for the culture of certain species, in
particular molluscs and crustaceans, phytoplankton plays a very important purifying and
bacteriostatic role. It appears thus that for the future primary and secondary productions
shall be irreplaceable in a hatchery productive system.
2. INTENSIVE PRODUCTION OF ZOOPLANKTON
Intensive production systems of zooplankton have reached an excellent level of
reliability.
TROTTA (1980 a ; 1980 d ; 1983) has recently described an intensive production
module of 100 million rotifers per day. This production level can largely satisfy the
requirements of an average size hatchery.
The intensive production method employed for zooplankton although surely valid
after verification and due to the results obtained, has also some disadvantages
especially from an economic viewpoint.
–
Very high investment costs.
–
Management costs ; energetic personnel.
Intensive production due to the aseptic requirements, needs in particular the
intervention of specialized personnel.
The investment and management costs of an intensive phytoplankton and
zooplankton production unit is really only suitable for large aquaculture facilities.
The intensive production method remains unequalled today but it could be
seconded by other systems of extensive production, in other words in large volumes.
3. THE PRODUCTION OF ZOOPLANKTON IN LARGE VOLUMES
The production of zooplankton (especially rotifers) following this method,
schedules the employment of very large culture volumes (10 - 80 cubic meters or more).
The fundamental differences between the culture of zooplankton carried out in
large volumes and intensive culture are as following :
– A non. monoxenous condition : several species of zooplankton and
phytoplankton are present in the culture at the same time.
–
The density of the plankton in rearing is lower (15 - 70 rotifer/ml on average).
3.1. Feeble density culture in large volumes
Let us take as example a tank of 70 cubic meters equipped with an aeration
system. The tank will be supplied with sea-water and if possible fresh water will be
added (Optimum salinity 25 ‰).
The water is fertilized with agricultural manure according to the formulas shown
in Table 1 ; the tank should be cleaned out first (IPPM bleach) so as to eliminate any
undesirable organisms.
The phytoplankton is inoculated in the tank, normally Chlorella sp is employed (3
- 4 cubic meters of culture at a density of 5-10 million cells per ml) ; After a few days
depending on the season and the light intensity, the phytoplankton reach a concentration
of 10 - 15 million celles per ml ; at this moment, rotifers from other cultures are
inoculated at the initial concentration of 4 - 10 ind/ml.
The rotifer concentration increases rather quickly ; when it reaches 15 - 20 ind/ml
(the colour of the culture changes very quickly from green to brown) yeast is given up to
a maximum of 500 gm per day for a 70 cubic meter tank). After a few days of rearing if
an important presence of protozoa is remarked, bleach is employed in the culture
medium itself, at a rate of 0.3 - 0.5 ppm. This operation permits the elimination of
protozoa without any dangerous effects being caused to the culture.
With this type of culture, we have reached concentrations of 30 - 60 rotifers/ml
with a maximum of 114/ml in Summer which corresponds to a production of 4 billion
rotifer (PONTICELLI et al., 1985).
At these concentrations, the culture will normally degenerate very quickly.
Therefore the technicians in charge should keep the concentrations below 50 - 60 ind/ml
by frequently collecting them every now and then.
3.2. High density culture in large volumes
This type of culture is mostly carried out for the present in Japan, in the larges
production centres of juveniles, employed for restocking.
A typical production unit for zooplankton will consist in 8 tanks, equipped with an
aeration system of 150 cubic meters.
After fertilization we must wait for the phytoplankton to reach a concentration of 5
- 10 million cells/ml. At this moment rotifers are introduced at a rate of 100 ind/ml. On the
second day of culture, fish liver oil enriched yeast is distributed at a rate of 500 - 2,000
g/day per tank.
In these types of cultures, the rotifer concentrations can reach 400 ind/ml, but in
a much shorter duration, two weeks at the most (more frequently not more than 6 - 7
days is required).
Thus every day in the tank, 2.3 billion rotifers can be filtered over several days,
At the TAKEHARA stocking centre in Japan, 1,221.8 billion rotifers were
harvested for the production of 4 million madai (red sea bream) in the period from April
to July (HENOCQUE 1984 - Fig. 1).
This method is thus based on the regular change and renewal of the cultures
(every 6 - 10 days).
However, the quantities of water, fertilizers and food required bring about high
costs.
4. EXTENSIVE PRODUCTION OF ZOOPLANKTON
For hatcheries located near brackish water lagoons, there exists another
possibility, through the zooplankton yield found in the bordering zones of the lagoons,
places where there exists very feeble renewals and eutrophic water.
A second possibility consists in the correct culture of zooplankton in fertilized
earth tanks (GEIGER, 1983 ; DOYLE et al., 1984).
These techniques were applied mostly in the South of France in the Languedoc
Roussillon region which has numerous wet zones, brackish water lagoons and salt
marshes (BARNABE, 1978, 1980, 1984).
While taking into account that the zooplankton concentration is rather feeble, the
most important problem to resolve is the perfecting of an automatic harvesting device ;
this harvest must be carried out quickly while not interfering with the plankton.
4.1. Description of a zooplankton collecting device
An automatic harvesting device for zooplankton (BARNABE, 1980 ; PONTICELLI
et al., 1985) consists in a PVC cylinder, 30 cm in diameter, 50 cm in length, in the centre
of which a propellor rotates by means of a 50 watt powered motor and a set of gear
wheels (see fig. 2). MORETTI, 1985).
The cylinder is maintained in a horizontal position below the water level by
means of floats of appropriate volume.
The propellor in rotating inside the cylinder provokes a constant water flow which
is filtered through a 4 meter long net which retains the zooplankton. A plankton net of
different mesh spacings is used depending on the size of the organism we want to fish
(The mesh spacings vary between 50 μm and 500 μm). The power drive is ensured by a
60 ampere-hour accumulator, connected to the motor by means of a 2 millimeter section
cable.
An electronic regulator of very feeble. electriC consumption, permits to vary the
rotation speed of the propeller between 80 and 250 rotations per minute.
This causes a water flow supply in the cylinder of between 70 and 400 liters per
minute.
The rotation speed is chosen in accordance to the zooplankton concentration ;
normally a feebler rotation speed is employed when there are very important
zooplankton concentrations or when the water contains a lot of organic matter in
suspension (The clogging up of the net can cause it to tear with a strong water flow and
thus the loss of the plankton is inevitable ) .
The collector is also equipped with a feeble power lamp (2 W) which, when night
fishing is carried out, attracts the zooplankton, and in this way, the yield efficiency is
improved.
The most abundant zoological groups are rotifers, copepods, ostracods and in
oversalted water tanks, Artemia.
The most interesting salinity rates for the production of zooplankton are those
varying between 10 and 20 °/00.
5. OXIDATION POND METHOD
The oxidation pond method is employed to purify polluted water coming from
small communities by means of large ponds : When the treatment is completed the
effluent possesses chemical and bacteriological characteristics quite similar to those of
water for bathing.
The oxidation ponds are quite large (1 ha around to purify waste water from
villages of 1,000 inhabitants). Normally, the oxidation pond method is carried out with the
use of three ponds known as stabilization ponds where the water flows through one after
the other. In the first pond, there is a very important bacterial activity, in the second one
a phytoplankton one and in the third a zooplankton activity .
The three ponds are shallow (1 m to 1.5 m so as to allow the complete
oxygenation of the whole water body and the penetration of light. The ponds are in an
"S" shape which helps in obtaining a maximum hydrodynamic effect in the oxidation
pond.
The zooplankton is represented essentially by groups of animals. Clliates which
consume bacteria, rotifers which consume phytoplankton and bacteria reaching
concentrations of 15O ind/ml, copepods (crustaceans of 200 - 500 μm) which mostly
consume phytoplankton and finally daphnids (large crustaceans of 1 to 3 mm).
Daphnids can reach a density of some hundreds of ind. per litre.
The production from an oxidation pond is enormous, 40 - 60 ton/ha/year of
pnytoplankton and 8-9 ton/ha/year of zooplankton (in a fresh biomass).
Zooplankton can be collected from the oxidation pond :
–
passively, by adapting a filter chute onto the outlet nozzle of the effluents,
–
by means of collectors similar to those already described here above,
–
by means of strainer-collectors ; in this case, the water is pumped, and let
flow over a series of rotating cylinder strainers of smaller and smaller space
meshings.
When the zooplankton has been collected, it can be directly employed to feed
marine species fry, such as sea-bass. BARNABE obtained good survival rates of seabass fry which were fed solely live zooplankton from day 40 to 100. Zooplankton may
also be dried or frozen.
6. SOME EXAMPLES
The ORBETELLO municipal hatchery (Italy) has carried out for several years
zooplankton production techniques while employing larger volumes (SALVATORI et al.,
1985).
Five tanks of 70 cubic meter are used in the hatchery, for the culture of rotifers
and copepods. Larval rearing takes place in 6 tanks of 18 cubic meters which have an
open circuit system. Indeed, a sea-water well will give 15 liters per second of water with
a constant temperature range of 25° C. The water from the well is mixed with the cold
sea water so as to obtain a temperature of 12 - 15° C for rearing.
Rotifers (produced according to the technique described in paragraph 3.1. in
tanks of 70 m3 ) are collected either manually by means of an automatic collector or
more frequently by means of a simpler collector equipped with an air-lift (ANGELINI.
pers. Comm. ; see fig. 3).
To increase the temperature in the rotifer culture tank a simple PVC pipe
exchanger was tested and gave good results.
The water from the well at 25° C, circulating through the pipe (tens of meters in
length) , heats the zooplankton culture water, and permits an increase in temperature of
3 - 4 degrees.
Two outside basins of 600 and 250 m2 are also employed for the extensive
production of zooplankton (rotifers, copepods , ostracods ).
The basins are fertilized by means of organic or inorganic agricultural manure.
The zooplankton is collected by means of an automatic collector. The collector
for the 600 m2 basin is installated near the foot bridge and can be operated automatically
at the time desired by the technicians. Indeed, a time clock can be set to start off the
collector during the night or in the early morning. On arrival at the hatchery, the
technicians will find a collection of several hours ready for distribution to the larval
rearing tanks.
From time to time harvests are also carried out in places located far from the
hatchery ; for example in a part of a lagoon of 40 ha, which is very shallow and eutrophic
or in low lying lands located below lagoon level and submerged during Winter by 30 - 40
cm of water which from time to time contains an abundancy of zooplankton.
In another aquaculture facility located in Southern Italy (ITTICA Ugento -LECCE)
the intensive zooplankton production in the hatchery is seconded by a outside
production in large volumes.
Indeed, following the sale of the eels, sea-bass and sea-bream in the month of
December some of the concrete tanks remain empty until the month of April. This period
corresponds exactly to the period of maximum need of zooplankton so as to feed seabass and sea-bream larvae.
The concrete tanks of 1,200 m3 are therefore fertilized according to the formula
which has been already stated here above and the zooplankton is collected by means of
an automatic collecting device .
7. CONCLUSIONS
The production of zooplankton which is the key to the productive process of a
hatchery remains one of the chief obstacles for the development of marine aquaculture.
Intensive rearing of zooplankton on micro-algae monoxenic cultures, although
verified and successful, requires very high investment and management costs.
It also requires specialized personnel which small and average size enterprises
do not always have at disposal.
The production of zooplankton in large volumes where the collection is carried
out by automatic systems, in very eutrophic lagoonal mediums, is an excellent
opportunity for many which have large surface areas at disposal or are located in the
proximity of a brackish water lagoon.
We may consider a situation as optimal when an intensive zooplankton
production at hatchery level, is seconded by a production carried out in large volumes or
by means of automatic collection in extensive basins.
Fertilizers
Quantity (g)
1
2
3
Ammonium sulphate
100
100
.-
Calcium oxide superphosphate
20
20
15
Clewat 32*
4
4
5
Urea
-
4
50
Clewat-32
FeCL3
(en %)
.6H2O
ZnCl2
0,385
CuSO4 5H2 0
0,007
0,166
(NH4 )6 Mo7 024 4H2O
0,632
MnCl2
.4H2O
0,776
H3 BO3
2,470
CoCl2
.6H2O
0,017
(HOOCCH2)2 NCH2 N(CH2COOH)*
* EDTA (Ethylene-diamine-tetraacetic acid)
TABLEAU 1 - Fertilizers employed according to three different formulas and Clewat 32
composition. Quantities indicated for 1 m3 of water.
(HENOCQUE, 1984)
Fig. 1 - Rotifer culture from April to July 1982 at the Takehara Center, in Japan.
(HENOCQUE, 1984)
Weight
Voltage
Motor drive
Min. speed
Max. speed
Max. flow
Min. flow
Min. absorbtion
Max. absorbtion
Fig. 2 – Automatic collector for zooplankton
Kg. 13
12 v
50 W
80 RPM
250 RPM
400 lt/1
70 lt/ 1
2A
3, 2 A
Fig. 3 - Rotifer collector operating withan air-lift
(M. ANGELINI)
CONTENTS
1.
Introduction
2.
Intensive production of zooplankton
3.
The production of zooplankton in large volumes
4..
3.1.
Feeble density culture in large volumes
3.2.
High density culture in large volumes
Extensive production of zooplankton
4.1.
Description of a zooplankton collecting device
5.
Oxidation pond method
6.
Some examples
7.
Conclusions
BIBLIOGRAPHY
BARNABE G., 1978 - Utilisation des chaînes alimentaires naturelles et du recyclage des
eaux usées dans la production à grande échelle de juvéniles pour
l'aquaculture. Publ. Sci. Tech. CNEXO ; Actes colloq., 7 : 221 - 238.
BARNABE G., 1980 - Système de collecte du zooplancton à l'aide de dispositifs
autonomes et stationnaires. In R. Billard, La Pisciculture en Etang.
I.N.R.A. Publ. PARIS : 215 - 220.
BARNABE G., 1984 - Utilisation de plancton collecté pour l'élevage de poissons marins.
In BARNABE G. et BILLARD R. Ed., L'aquaculture du Bar et des
sparidés, I.N.R.A. Publ., PARIS, 185 - 207.
DOYLE K., BOYD C., 1984 - The timing of inorganic fertilisation of sunfish ponds.
Aquaculture, 37 : 169 - 177.
GEIGER J.G., 1983 - A review of pond zooplankton production and fertilization for the
culture of larval and fingerling striped bass. Aquaculture, 35 : 353 - 369.
HENOCQUE Y., 1984 - Production de nourriture à grande échelle en écloserie. Rapport
de mission. Maison France-Japonaise. 8 pp.
MORETTI A., 1985 - Utilizzo di. zooplancton nei processi produttivi in acquacoltura.
Rapp. Fin. di Attività. Contratto ENEA N° 25073, 25 pp.
PONTICELLI A., ANGELINI M., LENZI M., SALVATORI R., 1985 - Raccolte di
zooplancton in ambienti eutrofici a mezzo di un'apparecchiatura
automatica. XVI Convegno S.I.B.M. - LECCE 25-30 Settembre 1984.
Oebalia Vol XI, N.S. : 181 - 186.
SALVATORI R., ANGELINI M., LENZI M., FOMMEI F., PONTICELLI A., 1985.
Allevamenti larvali di Dicentrarchus labrax Mediante utilizsazione di
acque ipotermali. Tre anni di ecperienze. XVI Congresso S.I.B.M..
LECCE, 25 - 30 Settembre 1984. Oebalia VOL . XI - 2. N.S. : 729 - 736.
TROTTA P., 1980 a - A simple and inexpensive system for continuout monoxenic culture
of Brachionus plicatilis Muller as a basis for mass production. In algae
Biomass ; eds shelef, C.J. Soencer and M. Balaban, Elsevier/North
Holland Biomedical press, AMSTERDAM.
TROTTA P., 1980 b - A simple and inexpensive system for continuous monoxenic mass
culture of marine microalgae, Aquaculture, 22 : 383 - 7.
TROTTA P., 1983 - An indoor solution for Mass Production of the marine microalga
Tetraselmis suecica Butcher. Aquacultural Engineering, 2 : 93 - 100.
INCREASED YIELDS_OF_ MARINE FISH AND SHRIMP PRODUCTION
THROUGH APPLICATION OF INNOVATIVE TECHNIQUES WITH ARTEMIA
Mr. P. SORGELOOS, P. LEGER, P. LAVENS and W. TACKAERT
Modern aquaculture production is achieved through complete domestication of
cultured species, e.g. fishes and crustaceans. This involves the elaboration of "egg to
egg" culture techniques contrary to earlier farming of wild caught fry. Mother animals are
induced to spawn in captivity. Their offspring are transferred to culture tanks where the
larvae grow onto a juvenile or post-larval stage. In the following "nursery" phase,
juveniles are conditioned for the transfer to natural conditions in the "grow-out" ponds or
cages where they are farmed up to a marketable size on natural plankton and/or
benthos eventually supplemented with prepared feeds, A small part of the harvest is
used to restock the "maturation" unit, closing the cycle.
Intensive larvae-production of most marine fishes and crustaceans is still
hampered by the requirement for live food, at least during their early stages. Since the
techniques for collecting or culturing their natural diet, characterized by a wide diversity
of plankton, are either commercially unfeasible or technically hard to realize, a suitable
substitute for natural plankton had to be found. The most used live food in the successful
larval rearing of fishes and crustaceans is the brine shrimp Artemia. Technically
speaking, the advantage of using Artemia is that one can produce live food "on demand"
from a dry and storable powder, i.e. dormant Artemia cysts (eggs) which upon
immersion in sea-water regain their metabolic activity and within 24 hours release 0.4
mm free-swimming larvae (nauplii). Actually more than 100 tons of dry Artemia cysts are
marketed annually for worldwide production of freshly hatched Artemia nauplii to be
used as food in the hatchery phase of fish and crustacean aquaculture.
The history of Artemia cyst production and use reveals an interesting evolution.
In the 1960's commercial provisions originated from a few sources in North America
which seemed to be unlimited. However, with the expansion or aquaculture production in
the 1970's, the demand for artemia cysts soon exceeded the offer and prices increased
exponentially. The dramatic impact of the aggravating cyst shortage on the expansion of
hatchery - aquaculture of marine fishes and crustaceans was repeatedly underlined at
international conferences. Especially the third world countries could hardly afford to
import the very expensive cysts.
Fundamental and applied research with brine shrimp Artemia was initiated at the
Ghent State University in the early 70's. Based on our (theoretical) knowledge we
claimed at the KYOTO 1976 FAO Technical Conference on Aquaculture that the cyst
shortage was an artificial and only temporal problem. During the following years, several
national and international aid organisations provided opportunities to verify our
theoretical claims and to prove the possibility of the local production of cheap Artemia in
various third world countries. As of today Artemia is being produced and exploited on the
five continents. In addition, demonstrations of integrated Artemia production have
been/are being set up in several third world countries opening interesting opportunities
for improved socio-economic situations.
Brine shrimp Artemia have unique characteristics which offer a great potential for
mass production purposes :
– In optimal conditions brine shrimp grows from larva to adult in less than two
weeks increasing in length by a factor 20, and in biomass by a factor 500;
– Abiotic as well as biotic requirements do not change throughout the animal's
development;
– Artemia can be cultured in a wide range of water salinities; i.e. from 10 ppt to
saturation level. Above 100 ppt, no predators nor food competitors survive resulting in a
monoculture under natural conditions ;
– Several hundreds of natural strains of Artemia are found in coastal salinas as
well as in inland salt lakes (rich in chlorine, sulphate or carbonate salts) found on the five
continents ;
– This crustacean can reproduce in two ways, either live reproduction (freeswimming nauplii) or cyst production (the embryos develop into gastrulae at which stage
they are encapsulated in a cyst shell and their metabolism is reversibly interrupted.
– Artemia has a high fecundity rate (more than 100 cysts or nauplii, every four
days) and a long lifespan (exceeding six months) ;
– Since this animal is a non-selective particulate filter-feeder, a wide range of
very cheap foodstuffs and fertilizers can be considered to culture Artemia, e. g. organic
manures (chicken dung), agricultural byproducts (rice bran, whey, brewer's yeast), etc...
– Artemia can be successfully grown in very high densities (i.e. more than
10,000 animals per liter) in salt water, and is not very demanding as to the qualitative
and quantitative composition of this water ;
– The adult brine shrimp has a very high nutritional value : i.e. its exoskeleton is
very thin (less than 1 um), 60 % of its dry weight consists of proteins, rich in essential
amino-acids ; Artemia furthermore contain significant concentrations of vitamines,
hormones, carotenoids, etc...
Proper knowledge of the biological and ecological (life cycle and habitat)
characteristics of brine shrimp reveal the potential to exploit existing natural sources of
cysts and biomass in operational saltworks (salinas) or salt lakes. The natural
distribution (better "dispersion") of Artemia can be enhanced by human intervention, i.e.
introduction (better "transplantation") of a selected Artemia strain into a suitable
environment (e.g. operational salina) can result in the establishment of new Artemia
populations which eventually can be commercially exploited. In regions with a
pronounced rainy season Artemia cannot resist predation during the wet season and
should be re-inoculated at the onset of the dry season when the salinity conditions can
support a monoculture of brine shrimp. Small ponds, manured with chicken dung can
yield up to 20 kg dry weight cysts or 1,500 kg live weight adult Artemia (so-called
"biomass") per hectare and per month. Although already at commercial operation in
artisanal saltworks in S.E. Asia, this type of Artemia production can be further optimized
and requires more extension services, in view of the beneficial effects of Artemia on
solar salt production, integrated production of salt and brine shrimp, eventually combined
with shrimp farming provide the most attractive cost-benefits, furthermore, this possibility
to valorize abandonned salinas or to revitalize solar salt production systems operated at
the limits of profitability (many examples in several third world countries in Asia and
America) opens interesting opportunities for socio-economic improvements in depressed
areas.
When conditions for pond production of Artemia are inappropriate (e. g. too low
salinity levels during the rainy season) intensive culture techniques with natural seawater
and micronized agricultural byproducts such as rice bran can be set up within the fish or
shrimp farm. Using batch or flow-through culture systems, bi-weekly yields of 5
respectively 25 kg live weight Artemia can be obtained per tank of 1 m3 content. The
production cost of Artemia biomass grown in intensive culture systems is much higher
than from wild harvests or pond produced biomass. Nevertheless, this new type of
controlled Artemia production can easily be integrated in the hatchery operations (similar
technical prerequisites), be operated on a year round basis, and moreover providing
better opportunities for quality control/manipulation (size, biochemical composition) of
the Artemia as a nursery and maturation diet (see further).
Improved technologies of cyst/biomass harvesting and processing (cleaning,
freezing|drying and packaging) should be applied as they influence the quality of the
endproduct.
In many situations, the utilization of Artemia in fish and shrimp farming can be
greatly improved. Although the production of nauplii from hatched cysts appears to be a
simple procedure, simple precautions have to be taken to ensure maximal hatching
outputs when incubating large quantities of cysts (e.g. optimal conditions for temperature
salinity, oxygen, pH, light and disinfection). For several reasons, the use of
"decapsulated" Artemia cysts are to be preferred in the fish/shrimp hatcheries. Through
oxidation with hypochlorite, the outer shell of the cysts can be removed without affecting
the viability of the embryo. Upon incubation in seawater, the hatching output of these
disinfected and naked embryos has increased and their nauplii have a higher energetic
value as compared to the nauplii produced from untreated cysts ; the use of
decapsulated cysts furthermore eliminates the needs of the cumbersome separation of
the nauplii from the empty shells.
Since the commercial availability of various Artemia originates from widely
different geographical sources, significant differences in larval culture success have
been reported with several fish and shrimp species. The Artemia nauplius size can be
too large for handling and ingestion by the larves. It is therefor advisable to start feeding
with frequent additions of freshly hatched nauplii from selected Artemia strains producing
small nauplii. So to reduce hatching operations and to ensure maximal valorisation of the
nauplii, high Artemia concentrations can be stored at low temperature for up to 48 hours.
Detailed biological and biochemical analyses revealed that the nutritional
composition of particular Artemia strains or even of specific batches from the same
strain docs not always meets the requirements of the fish or shrimp larvae. Probably, the
most critical factor determining the dietary value of Artemia as a food source for marine
fish and shrimp larvae is the presence and concentration of HUFA's (Highly unsaturated
fatty acids 20: 5 w 3 and 22: 6 w 3) which, in function of the strain or even the specific
batch of cysts from the same geographical origin might be inconsistent to minimal if
present at all. In order to overcome this variation in biological effectiveness of specific
Artemia cyst products, enriched diets have been formulated and bioencapsulation
techniques developed. Application of these new techniques result in significant
improvements of the nutritional effectiveness of the latter low quality cyst products ; i. e.
diets containing HUFA-levels are bioencapsulated in the gut of the Artemia nauplius
during its hatching incubation or after separation of the emerged nauplii. Using this
Artemia bioencapsulation technique, it has been demonstrated that hatchery production
yields can be increased considerably (i. e. higher survival, larger/ bigger larvae, better
disease resistance, fewer difformities, better pigmentation, etc... ) .
Because of limited availability, the use of ongrown and adult Artemia has mostly
been restricted to relatively small scale culture trials. During recent years, however,
commercial scale use of Artemia biomass harvested from local salt-works (especially in
S.E. Asian countries, but also Brazil, Panama and Ecuador) is gaining more and more
interest especially at nursery stage (in both fish and shrimp farming) and for the
maturation of penaeid shrimp. Feeding adult Artemia for one to two weeks to the
juveniles in nursery ponds or intensive raceways results in significant increases in
nursery survival and growth. A diet of adult brine shrimp not only is optimal for hatchery
reared fry at its transition from a controlled environment: to fluctuating conditions in the
Wild, it has also proven to be very useful for acclimating wild fry (e.g. milkfish) that often
have become weak as a result of excessive handling and transport.
In addition, it has recently been found that a diet of Artemia-biomass can improve
maturation success in several Penaeus shrimp species. Further enhancement of the
nutritive properties of the Artemia biomass can be achieved by application of the
bioencapsulation technique with enriched products (e.g. emulsified diets for
enhancement of maturation, better postlarval pigmentation, vitamin supplementation,
prophylactic treatment, etc...
The above stated developments of Artemia enriched diets have been at the
origin of the development of algal substitutes which are successfully applied for feeding
the first stages of penaeid shrimp (Zoe and Mysis). Unicellular algae production (e. g.
Skeletonema, Tetraselmis, Chaetoceros) not only is very costly (investment, energy,
products and labour), it has also been proven on several occasions that their nutritional
effectiveness may vary considerably throughout the year. In this regard, the availability
of an inert substitute, as an "off the shelf" feed, that will guarantee a constant and equal
performance in the hatchery outputs may be considered as a major breakthrough in
shrimp farming.
ACKNOWLEDGEMENTS
Research at the Artemia Reference Center is sponsored through the Belgian
National Science Foundation (Grant FKFO 32.0012.81) of which P. SORGELOOS is a
senior scientist ; the Belgian Administration for Development Cooperation (ABOS) ; the
institute for the Promotion of Industry and Agriculture (IWONL) and the NU Artemia
Systems.
LITERATURE OF INTEREST
LAVENS P., LEGER Ph., SORGELOOSP., 1986 - Production, utilization and
manipulation of Artemia as food source for shrimp and fish larvae. Ocean
is, 12 (4):
LEGER Ph., SORGELOOS P., 1985 - Nutritional engineering improves outputs of brine
shrimp Artemia. Aquaculture magazine, 11 (5) : 24 - 30
LEGER Ph., BENGTSON D.A., SIMPSON K.L., SORGELOOS P., 1985 - The use and
nutritional value of Artemia as a food source, Oceanogr. Mar. Biol. ANN.
Rev., 24 : 521 - 623.
SORGELOOS P., LAVENS P., LEGER Ph., TACKAERT W., UERSICHELE D., 1986 –
Manual for the culture and use of brine shrimp Artemia in Aquaculture.
Artemia Reference Center, State University of GHENT, BELGIUM, 319
pp.
SORGELOOS P., BOSSUYT E., LAVENS P., LEGER Ph., VANHAECKE P.,
VERSICHELE D., 1983 - The use of the brine shrimp Artemia in
crustacean hatcheries and nurseries : 71 - 96. In : CRC Handbook of
mariculture. Vol 1. Crustacean Aquaculture. McVey J.P. (Ed.). CRC
Press, Inc., Boca Raton, Florida, USA, 442 pp.
PERSOONE G., SORGELOOS P., ROELS O., JASPERS E.,(Eds) 1980 - The brine
shrimp Artemia. Volume 3. Ecology, Culturing, Use in Aquaculture.
Universa Press, WETIEREN, Belgium, 456 pp.
VERSICHELE D., LEGER Ph., LAVENS P., SORGELOOS P., 1986 - L'utilisation
d'Artemia. In : Aquaculture. Vol. 1. Barnabé G. (Ed.). Technique et
Documentation, Lavoisier, PARIS, France, 521 pp.
INTERNATIONAL STUDY ON ARTEMIA. XLII
THE EFFECT OF THE NUTRITIONAL QUALITY OF ARTEMIA ON THE GROWTH
AND SURVIVAL OF SEA-BASS (Dicentrarchus labrax L.) LARVAE IN A COMMERCIAL
HATCHERY
Mr. V. FRANICEVIC, D. LISAC, J. BUBLE, Ph. LEGER, P. SORGELOOS
1. INTRODUCTION
The quality of Artemia nauplii plays a very important role in the nutrition of marine
fish larvae. Very often mass mortality or fish lethargy have been reported when feeding
low quality livefood (reviews in WATANABE, 1983, and LEGER et al., 1986). It was
observed that nutritional quality of Artemia for marine fish larvae is mainly determined by
the content of essential fatty acids, i.e. the highly unsaturated fatty acids 20 : 5 w 3 and
22 : 6 w 3. Experiments at laboratory scale with larval sea-bass, Dicentrarchus labrax,
fed with enriched Artemia nauplii (ROBIN et al., 1981, VAN BALLAER et al., 1985)
pointed out the importance of this problem.
The purpose of this experiment was to define the influence of Artemia nauplii
quality (from the standpoint of HUFA) on the larval production figures in mass intensive
rearing of Dicentrarchus labrax.
2. MATERIALS AND METHODS
25 larval rearing tanks of 2 m were stocked with 40 000 larvae and fed the same
quality rotifers (Bracnionus pl;) for nine days. Culture water (38 ppt S, 19-20° C) was
exchanged at a rate of 30 % par hour. A natural photoperiod was applied not using
artificial light. After nine days five treatments (five replicates each; were started using
different qualities of Artemia nauplii from the standpoint of w 3- highly unsaturated fatty
acids (See table I and table II). Techniques used for the mass production of Artemia
nauplii from decapsulated cysts have been described in FRANICEVIC (l987). Artemia
enrichment was performed using an emulsified diet (SELCO, Artemia Systems, NV,
GHENT, Belgium) rich in HUFA. Enrichment was done in the hatching medium
according to the Procedure described by LEGER et al., (1987a).
The fatty acid profile of freshly hatched nauplii, and enriched nauplii was
determined according to the method described by LEGER et al., (1985 b). Wet weight,
length and survival of the fish larvae have been determined after 9, 23 and 42 days.
3. RESULTS AND DISCUSSION
Data for survival, mean length, mean weight and calculated biomass production
(= product of number of surviving larvae and mean individual weight) are summarized in
Table III. HUFA-factors were calculated for 20: 5 w 3 and 22 : 6 w 3 by multiplying the
mg/g values of these HUFA's in Artemia with the number of days these Artemia were fed
to be larvae.
The data in Table III indicate that growth is similar in all treatments until day 23.
At the end of the experiment, however, clear differences in both mean length and weight
are apparent. Those treatments which received w 3 HUFA enriched Artemia nauplii
(treatment 3 and 5) gave best results.
When relating calculated HUFA factors to growth data after 23 days Artemia
feeding it appears that w 3 HUFA in Artemia do not play an important role for larval
growth. A different picture, however, is seen after 42 days of culture, i.e. 22 : 6 w 3
content in Artemia and larval growth are clearly correlated. The level of 20 : 4 w 3 in
Artemia does not seem to play a determining role for growth (e.g. treatment 1 VS T).
Except for treatment 2 receiving freshly hatched Great Salt Lake Artemia nauplii,
differences in survival are not as pronounced. Mortality in treatment 2 was complete by
day 35, This confirms earlier observations by VAN BALLAER et al., (1985) who
suspected a possible interaction from pesticide contamination in this Artemia source.
Since we found satisfactory survival and growth in the larvae fed w 3 HUFA enriched
Great Salt Lake Artemia, we would rather minimize the interaction of contamination, and
stress the deleterious effect of the w 3 HUFA deficiency in this diet. A similar relation has
been reported earlier by WATANABE et al., (1982) for larvae of the red sea-bream
Pagus major.
Contrary to larval growth. survival indeed seems to be affected by the 20 : 5 w 3
content in Artemia (e. g. increasing survival with increasing 20 : 5 w 3 factor). For this
larval biomass production in Dicentrarchus labrax is directly related to the content of
both 20 : 5 w 3 and 22 : 6 w 3 in Artemia.
Our results have indeed proven that supplementation of essential fatty acids
through Artemia enrichment can significantly improve larval production success in
commercial intensive sea-bass farming. In view of the varying concentrations of 20: 5 w
3 among strains and even between lots of the same Artemia strain, and since the other
essential fatty acid 22: 6 w 3 is generally lacking in freshly hatched Artemia (LEGER et
al., 1986) HUFA enrichment is recommended as a routine practice in larval sea-bass
culture.
4. ACKNOWLEDGEMENTS
The authors wish to thank the staff of CENMAR and the Artemia Reference
Center for their technical assistance which enabled the experiments and the analysises
to be carried out.
Table I: FOOD REGIMES
Treatment
Food Regime
1
AF 858/24 (Artemia Systems N.V., GHENT, Belgium) freshly hatched Artemia nauplii
throughout (42 d)
2
GSL (Great Salt Lake, Utah, USA) Freshly hatched Artemia nauplii
throughout
3
GSL freshly hatched Artemia nauplii during ten days + GSL/S (Great Salt
Lake, 24 h enriched with Selco, Artemia Systems N.V.) Artemia nauplii
up to the end of the experiment
4
SFB (San Francisco Bay, San Francisco Bay Brand, CA-USA) freshly hatched
Artemia nauplii throughout
5
AF 858/24 freshly hatched Artemia nauplii during ten days + GSL/S Artemia
nauplii up to the end of the experiment.
Table II
W 3 HUFA content (expressed as area percent of total fatty acids and mg per gram dry
weight Artemia) in freshly hatched and enriched Artemia nauplii.
Artemia
AF 858/24
GSL
SFB
GSL/S
Area %
mg/g
Area %
mg/g
Area %
mg/g
Area %
mg/g
20 : 5 w 3
5.3
7.7
0.3
0.4
1.9
2.3
4.S
8.1
22 : 6 w 3
-
-
-
-
-
-
3.1
5.1
Table III
Data on mean individual length, wet weight, survival and calculated biomass of D. labrax
larvae fed different quality of Artemia nauplii (See Table I) ; also given are w 3 HUFA
factors, calculated as the sum of products of mg/g HUFA 20 : 5 w 3 or 22 : 6 w 3 in
Artemia and the number of days these Artemia were fed.
Length (mm) 23 d
42 d
Wet weight (mg) 42 d
Survival (%) 42 d
Calculated biomass (g) 42 d
HUFA factor d 23 for 20 : 5 w 3
HUFA factor d 23 for 22 : 6 w 3
HUFA factor d 42 for 20 : 5 w 3
HUFA factor d 42 for 22 : 6 w 3
Treatment
1
6.99
14.38
14.01
22.54
126.3
177.1
323.4
-
2
7.46
0
9.2
16.0
-
3
7.74
17.25
24.45
20.00
195.6
109.3
66.3
263.2
163.2
4
7.35
14.51
14.27
18.18
103.8
52.9
96.6
-
5
6.82
16.48
24.60
24.36
239.7
182.3
66.3
336.2
163.2
LITERATURE CITED
FRANICEVIC V., 1987. Large sclae Artemia cyst hatching at the CENMAR fish hatchery
in Yugoslavia. In Artemia research and its applications. Vol. 3.
SORGELOOS P., BENGTSON D.A., DECLEIR W., JASPERS E. (Eds).
Universa Press, WETTEREN, Belgium, in press.
ROBIN J.H., F.J. GATESOUPE, R. RICARDEZ, 1981. Production of brine shrimp
(Artemia salina) using mixed diet : consequences on rearing sea-bass
larvae (Dicentrarchus labrax). J. World Mariculture Soc. 12(2) : 119 - 120
LEGER Ph., D.A. BENGTSON, K.L. SIMPSON, P. SORGELOOS, 1986. The use and
nutritional value of Artemia as a food source. Oceanogr. Mar. Biol. Ann.
Rev., 24 : 521 - 623.
LEGER Ph., P. CANDREVA, E. NAESSENS-FOUQUAERT, P. SORGELOOS, 1987.
Techniques for the manipulation of the fatty acid profile in Artemia nauplii
and the effect on its nutritional effectiveness for the marine crustacean
Mysidopsis bahia (M). In : Artemia research and its applications. Vol. 3.
SORGELOOS, P., BENGTSON D.A., DECLEIR W., JASPERS E. (Eds).
Universa Press, WETTEREN, Belgium, in press.
LEGER Ph., P. SORGELOOS, O. MILLAMENA, K.L. SIMPSON, 1985. International
study on Artemia. XXV. Factors determining the nutritional effectiveness
of Artemia : the relative impact of chlorinated hydrocarbons and essential
fatty acids in San Francisco Bay and San Pablo Bay Artemia. J. Exp. Mar.
Biol. Ecol., 93 : 71 - 82.
VAN BALLAER E., F. AMAT, F.HONTORIA, Ph. LEGER, P. SORGELOOS, 1985.
Preliminary results on the nutritional evaluation of w 3-HUFA enriched
Artemia nauplii for larvae of the sea-bass. Dicentrarchus labrax.
Aquaculture, 49 : 223 - 229.
WATANABE T., 1983. Nutritional values of live organisms used in Japan for mass
propagation of fish : A review, Aquaculture, 34 : 115 - 143.
WATANABE T., M. OHTA, C. KITAJIEA, S. FUJITA, 1982. Improvement of dietary value
of brine shrimp Artemia salina for fish by feeding them on w 3 highly
unsaturated fatty acids. Bull. Jap. Soc. Sc. Fish., 48 (12) : 1775 - 1782.
REPRODUCTION AND LARVAL REARING OF PENAEIDS
Mr. F. LUMARE
Aquaculture is expanding on a worldwide level and although the shrimp-culture
production is comparatively low it tends to show a tremendous uprise trend. Table 1
compares the world aquaculture production in 1975 (Pillay, 1976) for yields obtained in
the years 1979-80 and 1982-83 ( Pedini, 1984). The data shows an increase of 688,1%
for Crustaceans.
Penaeids, mainly, play a relevant role in Crustacean production at present.
The increase in prawn farming is due to the solutions found for many
technological production problems , which may be summarized as follows:
a) the fry can be reproduced in great quantities and, above all, with profit;
b) the marketable size can be attained in 4-5 months. No other commercially viable
aquatic species can be compared with this:
c) the Penaeids become acclimatized to the most diverse environmental, socioeconomic, technical and management conditions of production so it is possible to
develop shrimp culture, in non industrialized and underdeveloped countries, in
extensive, semi-extensive and intensive conditions;
d) high demand of Crustacean on all the markets of the world due to the high evaluation
of this product.
The productive shrimp culture is developed on different systems according to the
environmental availability, the socio-economic structure, the shrimp species available
and their biological characteristics and, finally, the technological level of the country.
Table 2 shows the main different shrimp culture systems in the world.
A very effective system of the shrimp-culture process is based on different steps :
1) sexual maturity in captivity; 2) reproduction or spawning; 3) larval and post-larval
rearing; 4) pre-growing and 5) ongrowing to marketable size. This system has a closed
cycle and it is completely controlled at each step; like this the system gives the
assurance of success because it is able to give constant results in terms of number,
quality and cost of the fry production. But in this case the cost productions are, generally
speaking, higher than in the fourth system (see table 2) based on the fry collection in the
wild (a shrimp culture system adopted in Central America). In this last condition the cost
production of fry is very cheap and it may positively affect the whole shrimp-culture
process. But this system may also be affected by a very problematic point which is the
uncertainty of the fry collection. This is what happened in Ecuador, where, in March
1985, abnormally cold coastal water began to disrupt the spawning of Penaeus
vannamei and P. stylirostris, greatly reducing the supply of wild-post-larvae and gravid
females. As a result 40-70% of Ecuador's ponds were dry in early August 1985 because
of the shortage of seedstock.
In the traditional shrimp-culture system, as seen in Japan (table 2), sexual
matured females with well developped gonads (stage IV; table 3) are caught between
April and September in spawning grounds, at a depth of about 10 m and then the gravid
females with spermatophores (table.4) are transferred into spawning tanks. Here the
spawners are stimulated to release eggs by increasing the temperature of the water (
thermic stimulation) from natural conditions (18-21°C ) to the requested degree (2426°C).
In Italy, research on prawn reproduction and breeding began in 1970 with the
Mediterranean species Penaeus kerathurus. But this Penaeid appeared unsuitable for
culture due to the following causes :
1) P. kerathurus requires a long period ( about 17 months ) to reach a good marketable
size ( 30g);
2) it has low resistance to cold and it dies at 5-6°C.
Taking into consideration these points P. japonicus was introduced into Italy in 1979 for
culture purposes because:
a) it takes a short time, about 3-4 months for it to reach marketable size;
b) it can survive also at temperature drops of 1-2°C;
c) it is generally speaking, more resistant to handling than P. kerathurus ;
d) it is similar in colour , shape and taste to P. kerathurus so the new species did not
cause any commercialization problems or prejudices for consumption.
The introduction of Asiatic kuruma prawn raised the problem that as P. japonicus
is not endemic along the Mediterranean coasts it required a reproduction technology
settlement.
The successive experiments emphasized the reproductive biology of P.
japonicus the role of unilateral eyestalk ablation ( tab.5,6,7,8,9,10. 11, and 12) the
influence of the feeding quality (table 13), the effects of the photoperiods and the
importance of the environmental parameter, manipulation.
At present a technology has been perfected by which the sexual maturity of P.
japonicus is not merely induced but controlled, so that the reproduction of the breeders
can be synchronized ( tab.14). This means that the production of high numbers can be
obtained on large scale. To give an idea of the potential of the controlled system, one
single maturity controlled module ( 6m in diameter) contains an average of 300 females :
for every reproduction cycle, about 40% of the female population is ready to spawn.
From these, 85% spawn, on average 35,000 eggs at a time, releasing 50,000 eggs per
cycle (3-4 months), during which each female spawns 1.4 times. over the total
reproductive period (one spawning cycle for each month) 15,000,000 eggs are produced
in one single module which means about 3.8 million eggs in the single module for each
reproductive cycle. A commercial hatchery with at least 12 controlled tanks ( table 15)
can produce 45.5 million eggs per cycle and about 182 million eggs over the total
reproductive period (only four spawning cycles). By increasing the number of
reproductive cycles, using the same broodstock, this Figure can be doubled each
season.
The methodology for the mass production of fry has also been designed with
constant features and with high survival rates averaging about 60%, although in extreme
cases the survival rate might range between 40 and 100%. The final sizes of the P22
post-larvae average 24 mg in weight and 17 mm in length. The final production density
of the fry is currently more than 12 specimens (P22 )/litre . Table 16 shows reproduction
characteristics of Penaeids in main shrimp-culture areas.
One important aspect of the reproduction of P. japonicus in Italy is the decrease
in the hatch rate of eggs according to the progression of the F generations ( table 17 ).
In 1985 the hatch rate was 18% which is much lower than the 50% which can
generally be obtained from wild spawners. This low hatching rate might be due to the
reduction of the genetic variability when compared to the initial stock of Asian Penaeid ,
according to research carried out on ongoing. The population used in Italy in 1985 had
already reached generation F7. Despite this negative aspect, this can easily be
overcame by important new seed stock for broodstock reconstitution or by crossing old
sub-stocks at high numbers, the problem does not affect the large scale production of
larvae because of the plentifulness of eggs.
Another aspect regarding the production of larvae and post-larvae, (
tab.18,19,20,21,22,23,24) must be pointed out. The thorough research carried out for
about 10 years by specialized institutions on shrimp-pathology has made it possible to
plan the disease resolution while defining specific prophylactic measures based on
antibiotics and chemotherapy which prevent or reduce the action of the most common
pathogens.
The larvae and post-larvae feeding is a basic aspect of the hatchery production.
Table 25 shows general sequence scheme of foods supplied in Penaeid culture all over
the world.
Table 26 gives the feeding sequence in the larvae and post-larvae rearing with
the production costs in the Italian system which uses artificial food from P2-3 ( postlarvae 2-3 days old) to P22.
Table 15 shows a draft of hatchery facilities for the production of 1.4. million
Penaeus japonicus fry while comparing the controlled sexual maturity system (A) and
the stimulating system (B) only This point is basic because it influences the cost
production of P22 ( table 27) and then the effectiveness of releasing and culture
purposes. Table 28 shows the main characteristics of larval and post-larval rearing and
the pre-growing of Penaeids in the world.
1975
79-80
82-83
% INCREASE OVER
% INCREASE
THE LAST TWO YEARS OVER 1975
FISH
3,980,492 3,227,810 1,117,916
11.1
11.7
MOLLUSCS
1,051,341 1,908,016 1,957,570
0.9
86.2
123,115
20.1
688.1
1,051,793 2,206,181 2,393,782
2.8
126.9
CRUSTACEANS
SEANEED
15,663
71,221
TAB1. - Estimated world aquaculture production (t) in 1975 ( Pillay,1976) and the
years 1979-80 and 1982-83 ( Pedini, 1984)
P .japonicus;
Italy, France
Sexual maturity in
captivity
→ Reproduction →
Larval and post—larval
culture
P.japonicus;
Brazil
Sexual maturity in
semi -captivity
→ Reproduction →
Larval and post-larval
culture
→ Pre-growing → Growing
P.japonicus;
P.monodon;
Japan
South-East of Asia
Reproduction
Larval and post-larval
culture
→ Pre-growing → Growing
Restocking
P.semisulcatus;
P.vannamei;
Kuwait
Central
P.stylirostris;
P.monodon;
P.indicus;
P.orientalis;
Metapenaeus
ensis;
M. monoceros;
America
→
→
Pre-growing
Growing
Restocking
→ Growing
South East of Asia
Growing
Table 2 - Scheme of main management steps of shrimp-culture in the world.
UNDEVELOPED (U)
OR
I STAGE
DEVELOPING (D) OR
II STAGE
YELLOW (Y) OR
III STAGE
RIPE R OR
IV STAGE
SPENT (S) OR
V STAGE
TABLE 3 - DIFFERENT STAGES OF OVARY DEVELOPMENT IN PENAEIDS. ON
TOP, THE OVARY EXTENSION IN PENAEID.
PENAEUS KERATHURUS
Female. Thelycum between the bases
of the 4th and 5th pairs of thoracic
legs.
Male. Petasma on the first pairs of
pleopods.
PENAEUS JAPONICUS
Female. Thelycum with
spermatophore and stop pers outside.
Complete spermatophore on top.
Table 4 – Exterior genitals in Penaeids.
Male. Petasma.
Tab. 5 - Eyestalk of Penaeid (Decapoda, Natantia) showing pars ganglionaris X-organ
(PGOX), sensory pore X—organ (PS), sinus gland (GS), the X-organ-sinus
gland tract (TGOXGS) and the X-organ-sensory pore tract (TPSGX). AB, axonal
tract of brain neurosecretary cells. LG, ME, MI and MT represents respectively
the lamina ganglionaris, Medulla externa, Medulla interna and Medulla
terminalis, all parts of the optic lobe peduncle (from Carlisle 1953, reported in
Adiyodi K.G. and K.G.Adiyodi 1970.)
TAB. 6 - Methods of eyestalk removal in Penaeids: a) eyeball incision and squeezing; b) ligation or tying; c) electrocautery or using a
silver nitrate bar; d) cutting; e) pinching-crushing.
TABLE 7
Responses to unilateral eyestalk ablation in Penaeus kerathurus (tank nos 1 and 2, Table 1). Only the females surviving the latency
period are considered.
Spawning sequence
Females spawning
1
1
e
spawned2
4
5
7
8
10
7
3
1
1
1
18
14
8
5
2
1
1
1
83850
17640
72330
10610
80390
17930
84100
18860
80500
-
61000
-
69500
-
74500
-
10
12
8
4
-
-
-
-
41060
45820
64440
69500
1000003
770003
48000
29000
e
8424
5680
17880
16200
43000
-
-
-
n
10
12
8
4
2
1
1
1
1 Including females spawning only unfertile eggs.
2
6
16
n
Number of eggs
hatched2
3
24
Females spawning fertile eggs
Number of fertile eggs
2
, mean; e; standard error; n, number of females examined.
3 Negative difference between number of fertile eggs spawned and of eggs hatched due to errors caused by counting method.
Tank No
Impregnated females (%) Females with maturing
gonads (II-IV stages;%)
1
77.3
2
3
Unilateral eyestalk
ablation
22.7
No
58.3
8.3
91.3
17.4
4
78.3
5
69.3
Period (day) until first
spawning
Number of spawning
days in 19 days
-
0
No
-
0
Yes
5
4
26.1
Yes
5
5
8.7
Yes
6
5
Table 8 - Responses to experimental conditions of Penacus japonicus over a short period.
Tank Unilateral
No. eyestalk
ablation
1
Light
intensity
lux
Number of spawning Fertilized eggs rate
day
(%) (2 )
Fertile unfertile total (1) mean
range
No
1,290
3
2
No
2,200
15
3
Yes
1,500
61
4
Yes
2,000
61
5
Yes
3,500
69
0
11,500
3,833
0,06
202
Period (day)
before
starting
regular
spawning
202
50.0-100
61,000
2,904
0,50
39
143
5.0-100
231,500
2,080
2,83
5
31
59.28
5.0-100
224,000
2,433
2,57
5
5
61.14
10.0-100
465,000
6
6
3
72.00
36.4-97.8
6
21
77.39
53
114
42.45
29
90
52
121
Total number Mean no. of Spawning
of eggs
eggs
index (SI)
spawning, (3)
days
3,883
Period(day)
before first
spawning
4.40
Table 9 - Data on the spawning of Penaeus japonicus throughout the whole conditioning period ( in 225 days )
.(1) Spawning was considered fertile when fertilized and unfertilized eggs were found in the tanks.
(2) Fertilized egg rate (%) is considered on only fertile spawnings.
gt - period (day) of experimentation ;gn-period (day) of experimentation at constant number of females
Examination date
Tank No.
1
2
3
4
5
Mean impregnation
rate (%) on
examination
26.2.80
28.3.80
18.5.80
25.6.80
12.8.80
7/8/9.10.80
77.3
58.3
91.3
78.3
69.6
75.0
40.9
50.0
19.0
42.8
14.3
33.4
35.0
47.4
4.8
21.0
18.7
25.4
80.0
78.9
15.0
47.4
62.5
56.8
66.7
94.7
30.0
70.6
83.3
69.1
37.5
94.7
30.8
54.5
77.8
59.1
Table 10 - Impregnation rate (%) ( females with s ermatophores) during conditioning period.
Mean impregration rate (%)
over whole conditioning
period
56.2
70.8
31.8
52.4
54.4
Tank No.
Unilateral eyestalk
ablation
Number of moults
Females
Intermouling period (I)
males
Females
males
92
33.15
40.90
1
No
114
2
No
116
68
47.54
34.77
3
Yes
133
103
38.78
38.07
4
Yes
117
75
47.81
32.92
5
Yes
97
89
46.09
46.52
Table 11 - Intermouling periods (I) in Penaeus japonicus affected by different experimental conditions
and for both males and females.
Tab. 12- Penaeus kerathurus. Fluctuations in the mating of
ovaries rate of the breeder stocks. _ _ _ _ _ _=
mating rate; ________= ovaries maturity rate.
Tank
number
Eyestalk
ablation
Photoperiod
Light source
Lux
Feeding (1)
Tab. 13 - Penaeus kerathurus. Distribution of monthly fertile spawnings
expressed as r/R.100; r = fertile spawnings, R = breeders;
C. m. = Carcinus moenas: M.g. = Mytilus galloprovincialis;
V . g. = Venus gallina
TAB. 14 - Draft of hatchery facilities for 1.4 million Penaeus japonicus fry according
to controlling sexual maturity and spawning system (A) and to stimulating
system (B).
TABLE 15 - Commercial hatchery plant for the production of 20 million post- larvae p22 of
Penaeus japonicus.
SPECIES
AREA
TREATMENT
TANK
SHAPE/SIZE
MATERIAL (m)
P. japonicus
Brazil
Cement
P. japonicus
France
Environmental
conditioning
Selected food
Conditioning
Photoperiodism
P. japonicus
Italy
P. japonicus
Japan
P. monodon
PVC
Fiberglass
Environmental
Cement
Conditioning
Unilateral eyestalk
ablation
Thermic
Cement
stimulation
South-East Thermic
Fiberglass
Asia
Stimulation
Cement
Environmental
conditioning
Unilateral eyestalk
ablation
P.semisulcab Kuwait
Thermic
Cement
us
stimulation
P.aztecus
P.ducranum
P.setiferuo
North
America
VOLUME
(m3)
SPAWNED
FEMALE
RATE: EACH
CYCLE (%)
SPAWNING
NUMBER FOR
EACH FEMALE
MONTH
EGG
MATCHING
NUMBERS
RATE (%)
RELEASED
BY EACH
FEMALE FOR
SPAWNING
100,000
50
Circular (ǿ 5)
Tetragonal
(4x4x1)
Cylinder-conical
(0.7 ǿ )
(1.82 ǿ )
Tetragonal
(2x2x1)
(2x2x1.8)
20-16
50-70
1
0.5-2
0.6
15,000
58
4-7.5
Not
comparable
data
98
0.4
21,500
50-15
Tetragonal
Rectangular
(10x10x2)
(10x5x2)
Circular (0.7 ǿ )
50-200
30-60
1
400.000
Tetragonal
Rectangular
20x8x9x1.6)
30x10x1.8)
Thermic
Cement
Circular
stimulation
Fiberglass. (1.8-2 ǿ )
Unilateral eyestalk Marine
Tetregonal
soalation and
play-wood (5x2x2)
without
50
0.2-0.4
100
1
1.000.000
100.000
60-30
15-530
43-90
1
186,436(a)
N.a.d.
15-2
20
50
1
71 .000
231,000
309,000
72.8
P.varnamei
P.stylirostris
Central
Unilateral eyestalk Metal plastic Circular
and
ablation and not
(0.6-3.7 ǿ )
Southern
America
0.5-3.5
1
N.a.d.
100,000
200,000
45-80
TAB.16- Reproduction characteristics of Penaeids in main shrim-culture areas.(a) The figure refers to average nauplis numbers
hatched for spawning. N;a.d. = Not available data.
Year
Generation
Number of breeding
pairs of previous
generation
Number of hatchery
produced larvae
Mean hatching rate
(%)
1980
F2
2
2,000
50
1981
F3
50
80,000
40
1982
F4
100
500,000
22
1983
F5
300
750,000
33
1984
F6
300
1.250,00
20
1985
F7
300
1 .400,000
18
Table 17 - Data concerning lesina broodstock of Penaeus japonicus at various generations.
N1
N2
N3
N4
N5
N6
TAB.18 - Naupliar stages of Penaeus japonicus.
TAB. 19 - PROTOZOEA I
TAB. 20 - PROTOZOEA II
TAB. 21 - PROTOZOEA III
TAB. 22
TAB. 23 – MYSIS IV
TAB. 24 – POST-LARVA I
STAGE EGGS
F
E
E
D
I
N
G
NAUPLIA ZOEA
1
6
1
2
3
MYSIS
1
2
3
POST-LARVA
1
2
3
4
Nitzchia sp.,Cyclotella nana
Thalassiosira sp. ,Skeletonema
costatum
Tetraselmis sp., Chaetoceros sp.
Phaeodactilum tricomutum
Soya-bean meal
Marine yeast (Candida sp.)
Frozen algae
Brachionus sp.
Copepoda
Artema salina (nauplia)
Frozen adult Artemia
Crushed meat of clam, mussel,fish
and squid
Artificial food
TAB.25- Sequence scheme of foods supplied in the culture of larvae and post-larvae of Penaeids.
5
10
20
35-65
DIATOMS
0.8 lit.
ARTEMIA
NAUPLIA
2.9 lit.
ARTIFICIAL FOOD .
1.2 lit
x 1,000,000 di
P22:
Fito
800,000 lit
Artemia cysts
13 kg (226,000 lit/kg)
Artificial diet
60 kg (20,000 lit/kg)
–Feeding cost incidence for each post- larva P22 = 4.9 lit
–Management cost and other items incidence for each post-larva
P22 = 19-28.9 lit
–Analysis costs referred to hatchery capacity of 20 millions P22
TAB. 26- Feeding sequence and production costs in the intensive culture of Penaeus
japonicus post-larvae.
Number of tanks employed
Conditioning
and
sexual
maturation
Tank volume ( m3)
Number of sea water changes
Total utilized sea water volumes
Cost production incidence of sea
water heating and recirculation on
each P22 (LIT)
Total tank volume (m3)
Egg incubation, larval Number of sea water changes
and post-larval rearing
Cost production incidence of sea
water heating and recirculation on
each P22 (Lit)
General services of
water and Geration
Phytoplancton
Artemia nauplio
Frozen Artemia
Feeding
Artificial diet
Feeding cost incidence on each P22
( Lit)
Labour cost
General cost incidence
on each P22 (Lit)
SYSTEM A
1
SYSTEM B
10
17
12
2
2
34
10.38
240
74.68
33
70
1
1
3.99
8.46
0.54
3.78
0. 84
2.94
0.84
2.94
11.75
1.20
4.98
15.53
8.87
28.96
8.87
111.32
TAB.27- Comparative cost incidence on penaeus japonicus fry production between
controlled sexual maturity and spawning system (A) and the stimulated one
only (B). Heating cost figures in A system refers to 10°C average temperature
in the sexualmaturity conditioning and hatchery production period (NovemberJuly) and then with a thermic expensive regime on the northern Adriatic Italian
coasts, in the Southern Italian areas the figures correlated to heating costs may
be cut by 50 per cent.
SPECIES
AREA
P.japonicus
Brazil
P.japonicus
France
P japonicus
P japonicus
Italy
Japan
P.monodon
SouthEast Asia
LARVAL AND P0ST-LARVAL REARING
PRE - GROWING
TANKS
DENSITY
FINAL
FINAL
FINAL REARING TANK SURFACE DENSITY INITIAL INITIAL FINAL FINAL SURVIVAL
PRE2)
(SP/m2)
STAGE SURVIVAL WEIGHT PERIOD MATERIAL (ha)
SP/M
STAGE WEIGHT STAGE WEIGHT RATE (%) GROWING
RATE
(mg)
(DAYS)
(mg)
PERIOD
MATERIAL VOLUME START END
START END
(DAYS)
(m3 )
Cement
16-20
N.a.d.N.a.d. P8-10
70
15
18-20
Earth
3.0
40-50 36
P40-58 1-2
56
30-50
42
P.V.C.
0.5-2 200,000 20,000P1-2
60-40 10-15
10-35
Fiberglass
8
250.000 50,000P5-10
47
P20
Cement
4-7.5
20,000 12,000P22-25
60
24
30
Cement
50-200 10,000 5,000P20
20-63 10-20
30
Sand
0,4
90-175 80
P35-65 1-2
17
15-45
20,000 10.000
350-600 400
54
Cement
4-25
2,000P5
30-40 N.a.d. 15-30
Cement
2,000 1.800
P45
0.2-1.5 6
30-35
32
P. semisultatus Kuwait
P.aztecus
P. ducrarus
P. setiferus
P.vannamei
P. vannamei
Cement
50,000 3,000P12
P20
15
30,000
530
1-2-20 100.000
500,000
7,500P20
57,500P40
21,000 P1-2
86,000
North
Cement
America Fiberglass
Marine plywood
Central Fiberqlass 1.5-10-20 40,000 20,000 P14
and
100,000 50,000 P5-6
Southern
America
10-30
2.3
21.2
38-50
29.1
30-50
N.a.d.
13
20-40
50
N.a.d.
10-24
Clay
Sand
Fiberglass
Marine plyMood
0.015
0.2
0.01
0.02
5,000
.
Claysand
0.5-4
50
200
25- P1-10
100 P14
36
0.0050.60
P45-50
0.5-1
25-60
20-65
THE PRODUCTION OF SHRIMP POST-LARVAE
Example : The present situation of hatchery Penaeus japonicus
Mr. G. LE MOULAC, Mr. C. DE LA POMELIE
1. INTRODUCTION
The control in the reproduction of certain Peneidae species is the outcome of an
important effort made in research over the past ten years.
Many studies have been made on the control of maturation (CAUBERE,
LAUBIER-BONNICHON). The MEREA team (PALAVAS Station) along with the
AQUACOP team (Centre Océanologique IFREMER du Pacifique) have got under control
the larvae rearing of many peneidae species especially :
–
In temperate waters : P. japonicus
– In hot waters (Intertropical or subtropical zones) : P. monodon, P. stylirostris,
P. vannamei, these two latter species can be of interest for the hotter zones of the
Mediterranean strip.
The hatchery phase for all these species covers three principal stages : Stockingmaturation, larvae spawning-rearing ; and eventually first fattening.
The example of the P. japonicus is given here.
2. STOCKING
The production of a large number of post-larvae during the productive season is
directly linked to the state of the broodstock at this precise moment.
A protocol was implemented so as to avoid mass mortalities linked with the
pathogenic agent, Fusarium solani and in these conditions, there is an excellent survival
rate throughout the nine months- of stocking and spawnings take place the whole year
round (Diagram 1 and 2).
3. MATURATION
Maturation takes place at l8° C all year with a natural photoperiod without
epedonculation (Diagram 2)
The maturation rate, obtained from controlled spawning is 50 %.
4. SPAWNING
Spawning is provoked by thermic shock. From 18° C, the animals at a maturation
stage of 4, 5 - 5, were submitted to 25° C.
Spawning took place around 3 days afterwards. The number of eggs collected
per female was 200 000.
70 % of nauplii is then recovered.
5. LARVAE REARING
Larvae rearing is carried out under strict supervision- The control of the feeding
sequence of the food quality and the pathological prevention, allows survivals rates of 70
% with final loads in rearing (110 to 150 P 3 per liter) (Diagram 3).
The speed of development of the larvae depends on the temperature.
The feeding sequence can be seen in diagram 4.
The principal pathogenic agents remarked in larvae rearing are the "imperfect"
fungus (Logidinium calinectes) and bacteria. The former is controlled with a fungicide
(trifluraline) which is used as a means of prevention, and inhibits the sporulation of this
fungus. This product is used continuously, from egg to P 1 stage. Bacteria is controlled
with the use of an antibacterian (furazo-lidone) which is employed from Z 1 to M 1 stage.
6. FIRST FATTENING
The rearing is carried out for another 20 days, in clear water with a good water
renewal.
The average survive! rate, during this period, is 70 %.
The feeding sequence (Diagram 6) is established for a range of temperature of
23 - 25° c.
The growth is exponential (Diagram 5)
The post-larvae are sold from P 23 to P 25, between 12 and 15 mg.
There exist no important pathological problems. This period of rearing does not
require any treatment.
7. TECHNICO-ECONOMICAL ANALYSIS
The control of all these parameters, the repetition of the results, have permitted
the analysis of the production costs for each of the rearing stages in a hatchery (Table 1)
The definition of the production costs permits having at disposal an efficient
programmation utensil for the productivity benefits. We discover that some are not as
important as believed (efficiency, and not investment).
Animals
Heating
Pumping
Air
Food
Manual labour
P.H F. H.T.
Broodstock %
11
27,5
2,7
0,3
5,1
53,2
120,9
Nauplii %
75
10
0,6
15,5
1,62/1000 N
P3%
36
6,5
41
16,4
6/1000 P 3
P 23 %
25,3
16,8
1,8
0,9
50,3
5
34/1000 P23
Table 1
8. TRANSFER
The reliability of the technique, along with the technico-economical analysis,
shows that the production of shrimp, at post-larvae stage, is profitable. The transfer of
this technique was carried out in GAEC "Les Poissons du Soleil" by MM. BALMA and
CAUBERE in BALARUC-LES-BAINS. This hatchery which carried out pilot productions
for two years (2 000 000 post-larvae) is now building a facility with a capacity of 10 000
000 post-larvae at first fattening stage. Another hatchery, the SCA Mari-Aude (Mr. LE
BITOUX) should start operating this Spring. Finally, in the PALAVAS Station a training
course was held for hatchery shrimp technicians and this permitted to answer the
demand of transfer for 5 other hatcheries for molluscs or fish.
If the production of post-larvae has developed, it is due to the fact that the results
obtained are very encouraging for fattening in the Mediterranean and on the Atlantic
coast.
Outside France, France Aquaculture, a sub-company of IFREMER has greatly
contributed to the development of shrimp rearing in intertropical zones, while employing
three major species : P. monodon, P. stylirostris, P. vannamei. The two latter species
and moreover P. stylirostris could be suitable for the hotter zones of the Mediterranean.
9. HATCHERY DEVELOPMENT IN FRANCE
The production of shrimp should enhance production in hatcheries which already
exist.
In France, two hatchery productions exist which are marketable ; fish fry (seabass and gilthead sea-bream) and mollusc spat (clam and oyster).
The production season of shrimp post-larvae follows the fry production season of
fish. The shrimp production is feasible in these facilities. The only additionnal facility
required is the room for the production of unicellular algae.
In a hatchery that produces mollusc spat, algae is no problem as this production
is the food basis for fry.
Another possibility lies in the creation of a monospecific hatchery for shrimp
which could integrate a flattening farm.
The cost price of shrimp post-larvae should be around the production cost, as is
remarked in hatcheries for mollusc and fish, the depreciation and the expenses have
already been taken into account in the cost price of fry and spat.
In the case of a hatchery which integrates a fattening farm, the purchase price of
post-larvae is not the same is the Commercial price found on the market of post-larvae
(0,15 Frs) ; the price of the post-larvae will be the cost price without manual labour, as
the manual labour comprehends all production (post-larvae and fattening)
Production cost : 0,03 Frs/ P 25
Monospecific hatchery cost price : 0,10 to 0,14 Frs/ P 25.
Figure 1: BROODSTOCK’S SURVIVAL RATE
Figure 2: BROODSTOCK SPAWNING
Figure 3: REARING LARVAE SURVIVAL RATE
Figure 4: REARING LARVAE FEEDING
Figure 5: PREGROWING FEEDING FOR 100 000
Figure 6: GROWING CURVE OF POST-LARVAE
LARVAE REARING OF BIVALVE MOLLUSCS
Mr. G. ROMAN
1. INTRODUCTION
Bivalve mollusc culture can be started in two different ways : collecting the seed
naturally or by hatchery rearing. Some of the advantages and disadvantages of both
methods are shown in the table below.
Natural collection
Advantages
– Low price
– Spat ongrowing on collectors
– Skilled labour not required
Disadvantages
– Environmental conditions not controlled
– Seasonal and short settlement period
– Heavy broodstock in the area is essential
Hatchery rearing
Advantages
– Environmental conditions controlled
– Settlements during most: of the year
– Parental stock small
Disadvantages
– Expensive building and maintenance
– Spat on-growing in nursery
– Skilled labour required
Larval rearing in big ponds is halfway between the two methods, and not
employed very often.
The choice between hatchery rearing or natural collection depend on the
characteristics of the area. As a general rule, natural collection is suggested if working
with cheap molluscs or in areas with rich stocks.
Hatcheries developed as a consequence of a decrease in oyster catches, owing
to poor recruitments. The causes of the shortage of juvenile oysters have been attributed
to the depletion of Fishery grounds, diseases, natural catastrophe and estuarine
pollution. As oyster industry required juvenile oysters in numbers that natural settlements
could not meet, hatcheries were developed to supply this industry with oyster seed.
Another reason for the development of hatcheries has been the possibility of
obtaining genetically selected stocks.
Most of the Atlantic European hatcheries have been working with oyster and
clam, formerly Ostrea edulis and Vencrupis decussate, and nowadays with the easy
culture and faster growing Crassostrea gigas and Venerupis semidecussata (=
Ruditapes philippinarum).
However, oysters and clams are not the only commercially important molluscs,
and some effort is devoted to the culture of pectinids (Pecten maximus, Chlamys varia,
C. opercularis), with promising results both in hatcheries natural collection.
Hatchery bivalve rearing on a commercial basis started in the 60's, and in some
way this can be related to the publishing of the following documents : LOOSANOFF &
DAVIS (1963), WALNE (1963, 1964, 1965, 1966) and IMAI (1966), describing culture
techniques, water processing, conditioning, phytoplankton production, etc...
Nevertheless, in previous years, it was necessary to find out about larval food
requirements. Also to this effect, LOOSANOFF's discovery (1945) that sexual ripeness
could be brought about by increasing the temperature, allowed a longer working period
and a faster development of hatchery techniques.
However, even now, there are more unknown factors in larval rearing leading to
sporadic and intermittent failures.
2. REPRODUCTIVE CYCLE OF BIVALVE MOLLUSCS
When culturing bivalve larvae it, is convenient to know something about the
sexuality of molluscs. It is necessary to known when and how the mollusks you are
going, to culture reproduce.
Most of the species have separate sexes, that is, some individuals are always
males, some of them are always females. However, some commercially.
Juveniles
Growth
Planting
Nursery
&
Planting
The right hand side of this table shows the characteristical procedures to be
carried out in a hatchery. We must add to them the selection of the brood-stock, food
culture and water processing,
2.1. Conditioning
In temperate waters the reproductive cycles of bivalves usually occur on a yearly
and sometimes bi-annual basis, and the spawning period is very short. Before the
experiments of LOOSANOFF & DAVIS (1963) larval rearing was limited to the very short
natural periods of spawning, but the conditioning techniques they developed allowed a
longer period of spawning, at least for some species.
The conditioning method involves placing the molluscs in water whose
temperature is increased daily until it reaches the required level. In this way,
gametogenesis can be induced after one month in animals remaining in a resting phase.
If the animals are undergoing the gametogenesis, this will be accelerated. Unless the
animals overcome the recovery phase, the conditioning techniques won't work, During
this period the animals must store nutrient reserves, consisting mainly of glycogen. That
is the reason why we must have a thorough knowledge of the reproductive cycles in the
animals we are working with.
2.1.1. Broodstock selection
Origin, aspect and meat quality are factors to be considered when selecting the
broodstosk. Animals coming from polluted areas or infested with parasites must be
rejected. Animals that appear very old, that are slow growers or that have a bad
appearance should be discarded.
Some animals must be opened, and the batches with a higher condition index
selected.
When working with animals that change their sex with age, different ages must
be conditioned, to be sure both sexes will be present.
Before introducing the animals in the conditioning system, they must be cleaned
and brushed carefully.
important species are hermaphrodites. COE's (1943, 1945) categories of
hermaphroditism are as follows :
– Functional hermaphroditism : spermatozoa and ova are produced
simultaneously, and self-fertilization may occur : Pecten maximus, Chlamys opercularis.
– Consecutive hermaphrodites, where there is a single sex reversal in life.
Usually, the sex change is from a younger male to and older female phase : Mercenaria
mercenaria.
– Rhytmic consecutive hermaphroditism : a male phase is followed by a female
one and then a male phase and so on ; Ostrea edulis.
– Alternative sexuality : in this case, a sex change occurs in adults that function
seasonally as separate sexes. This sex change is erratic and not predictive :
Crassostrea virginica.
However, regardless of the difference in sexual behaviour, all the commercially
important bivalves release their sexual products in the sea water, where fecundation
takes place (except the genus Ostrea).
The reproductive cycle in pelecypods can be divided into three main stages :
–
Gonad development
–
Spawning and fertilization
–
Development and growth.
Hatchery management involves these stages as follows :
Gonad development
Recovering
Ripening
Conditioning
Spawninq and fertilization
Ova + Spermatozoa
Development and growth
Embryogenesis Trochophore larvae
Veliger larvae Metaporphosis
Stimulating
Incubating
Larval rearing Settlement
2.1.2. Number of animals to be conditioned
This number will depend on the number of larvae required. If we can determine
the mean number of larvae produced by a female, and the mean number of females who
will spawn in each period of the year, it is easy to determine the required number of
animals to be conditioned.
The table below shows the percentage of oysters (Ostrea edulis) that spawned
after a three month conditioning period in different seasons of the year.
Conditioning Start
Autumn
Winter
Spring
Summer
Percentage of spawnings (swarmings )
1st month
2nd month
4.0 %
0.0 %
2.0 %
12.1 %
8.0 %
10.6 %
6.7 %
6.8 %
* The mean number of larvae produced at each swarming is 0.96 ± 0.54 x 10
3rd month
14.9 %
10.5 %
8.8 %
3.5 %
6
2.1.3. Conditioning systems
There are two types of conditioning systems, a flow-to-waste system or a
recirculating one. Probably the best results are obtained with the flow-to-waste system,
although it is more expensive, owing to the waste of food and heated water.
The water flow will depend on the volume filtered per animal, but usually less
than this volume is employed to reduce the cost of heating the water and the food
demands. When working with Ostrea edulis, high flows can result in larval losses, due to
clogging of the filters used to retain the larvae.
We usually give a flow rate of 1.2 l/oyster/hour- WILSON (1981) gives 1-2
l/oyster/hour. DUPUY et al., (1977), however, use a flow rate of 10 l/oyster/ hour.
Food ration : The energy requirements for building up the gametes must be
provided to the animals as food. The incoming water may or may not be filtered. In the
last case some food can be present in the water, but usually this is not enough for the
molluscs requirements ; so, some food must be added.
In most cases, the food given is live unicellular algae, but sometimes corn-starch
is added.
WILSON (1981) adds an amount of dried algal weight equivalent to 6 % of the
oyster dry meat weight. For 1 g of dry oyster, this represents 60 mg of dried algal weight
(= 2.64 x 108 cells of tetraselmis suecica or 1.74 x 109 cells of Isochrysis galbana).
HELM et al., (1973) add 10 Tetraselmis/ul, and FLASSCH et al., (1973) 2.16 x
108 cells tetraselmis/oyster/day.
DUPUY et al., (1977) recommend 2.0 mg/l of corn starch.
ROMAN (1985) feeds oysters on a mixture of 2.4 x 108 cells of Tetraselmis
suecica plus 3.1 x 108 cells of Skeletonema costatum per oyster and day (= 8.3 cells of
T. suecica plus 108 of S. costatum per microlitre.
The system must be cleaned periodically, mainly if corn starch is added.
When working with species other than oysters (Ostrea), frequent ripeness
controls must be performed. This is clone to avoid spontaneous spawnings in the system
owing to the temperature increases in the water where the animals are held. When the
animals are nearly ripe, a slight decrease in the temperature is recommended, and we
must bear in mind that males reach ripeness before females.
Oysters (Ostrea edulis) have a very characteristic reproductive behaviour, so I
will now describe the system we use for conditioning and collecting the larvae. A
diagram of the tanks where the oysters are held is shown in figure in these plastic tanks
(60 x 54 x 40 cm) 25 oysters are placed. The outflow must pass through two filters, 200
and 80 μm mesh size. When a swarming or larval release occurs, the larvae have a
tendency to swim at the very surface of the water. Then they are carried away with the
out-flowing water and retained in the 80 μm filter.
2.2. Stimulating
On natural conditions when the gonad reaches its maximum development and
the gametes are completely mature, spawning occurs, probably as a response to
environmental changes.
There can be spontaneous spawnings in the conditioning system. When this
happens, most of the gametes are not fit for culture, and they must be rejected.
To avoid this problem, when animals are considered to be ripe, they must be
stimulated under controlled conditions, to pick up the gametes when spawned. If
stimulation is not possible at the date, water temperature in the conditioning system
must be decreased ; however, stimulation is recommended as soon as possible,
because old gametes can result in bad larvae.
Before stimulating, the animals must be cleaned, and detritus and faeces
removed, as well as other organism settling on and in the shell, as they can spawn as
the same time as the molluscs.
Methods used in stimulating molluscs to spawn
In a recent paper, LE PENNEC (1981) reviews the methods employed to get the
molluscs to spawn. the methods most often employed are thermical changes, gamete
addition and physical and chemical shocks. It must be made clear that these methods
will only succed if the animals are ripe.
– Thermical changes : By far the system used most often. Usually, the rature is
raised 5 - 10° C. Once the required temperature is reached, it can be kept at that level,
or there can be increases and decreases for some time.
– Addition of gametes : This system is usually employed together with
temperature increases. In this way, the results are improved,
– Chemical stimulation : The latest trend is the use of serotonine injections. In
this way, fantastically rapid spawnings can be obtained, but usually only the males
spawn.
When warming the water for stimulating, as the gas solubility decreases small
bubbles are formed. When animals to be spawned fit inside these small bubbles, the
spawning can be prevented. The presence of bubbles is easily noticed by the
appearance of floating faeces. The warmed water must be aerated to avoid this.
The time required for spawning after starting to stimulate will vary according to
the species, ripeness, the system employed for stimulation, etc... Spawning can start a
few minutes later, or it can be delayed several hours. It may also not take place at all. In
fact, in our experiments with Pecten maximus, the release of gametes can be delayed 23 weeks.
When animals start to spawn, they must be placed separately in flasks filled with
water at the same temperature as those used in the spawning trays. When a female
happens to be a heavy spawner, she must be changed to another flask again.
When working with functional hermaphrodites, the spawners must be watched
continuously. Usually, as in the case of molluscs having separate sexes, the first
spawners are males, and when the testis is empty, eggs are released. A watchful and
steady survey of the flasks where the animals are spawning allows you to detect when
the sex reversal takes place. At this moment the animal must be seized and washed
inside and out, to remove as much sperm as possible and then placed in a new
container, to allow it to release the eggs. The survey must continue, because in some
cases, when test is are not empty, new sperm releases can occur.
In this way, we obtain eggs and sperm from different animals in separate
containers. Then, we may or may not put all the eggs together in a bigger container,
depending on our interests. In any case, and after adding some drops of a pooled sperm
suspension, they should be examined microscopically, to ascertain the percentage of
fertilization. If necessary, more sperm must be added. Fertilization must be performed as
quickly as possible, and no later than one hour after spawning. Where working with P.
maximus it is almost impossible to prevent a variable and uncontrolled percentage of the
eggs to be fertilized before sperm addition).
Next, eggs are passed through a 100 μm mesh, to remove detritus, and retained
either on a 20 μm mesh or in a container. Immediatly after, they should be counted and
placed in the incubations tanks.
All these operations must be done as quickly as possible. A delay in adding the
sperm can result in a low rate of fertilization. If eggs are filtered late after fertilization.
when the cleavage is in progress, a high amount of abnormal larvae can appear.
The number of eggs that a female can release depends on the species and the
size of the animal. We have counted 7 to 14 x 106 eggs, 68 μm diameter, in 10 cm length
scallops (ROMAN & PEREZ, 1976), and 1 to 2 x 106 eggs, 70 um diameter, in clams
(Venerupis decussata and V. pullastra) (PEREZ et al., 1977). Crassostrea virginica can
produce 25 to 100 million eggs (DUPUY et al., 1977).
2.3. Incubating
After spawning, the germinal vesicle in the spherical egg is visible. Later on, the
germinal vesicle breaks down and the egg remains in this stage until it is fertilized. Then
comes the rapid appearance of the first and second polar bodies, the fusion of male and
female pronuclei proceeds and cleavage starts. 12 to 24 hours later the trochophore
appears, and the next day, that is, 48 hours after fertilizing, the veliger larvae are
developed.
These development stages are performed in incubation bins, which must not be
disturbed during the 48 hours period. This is a short but important phase in larval culture,
and during this time neither food nor aeration is supplied to the larvae.
We usually add 500 to 2 000 eggs per square cm, and get 10 to 68 % of normal
larvae (PEREZ et al., 1977, GONZALEZ & ROMAN, 1983, ROMAN & PEREZ, 1976).
The bins we use for incubation purposes are either 100 l volume,1 900 cm2
bottom surface, or 400 l, 9 500 cm2 bottom surface.
After the 48 hours period, the drums are emptied, and the water is passed
through and 100 and a 45 μm mesh size filters, in order to retain the detritus (100 μm)
and the larvae (45 μm) in their early veliger stage or straight-hinge stage by this time
measuring about 100 μm. The filtering out must be done at a slow rate, to prevent
clogging and larval losses. Next, the number of normal and abnormal larvae is counted,
and the larvae are placed in the drums used for their culture at the required density.
Abnormal larvae are always present, but in a variable percentage and degree of
abnormality. Most of the misshaps in development belong to the following categories :
–
After fertilization, no development occurs, and the egg desintegrates.
–
Development stops before reaching the trochophora stage.
–
The trochophora does not secrete the shell.
–
Only a small and abnormal shell is produced.
– The shell looks normal, but either velum can not retract inside or it is
deformed.
–
The hinge is curved.
– The shell and velum are normal, but the larvae do not feed, and as culture
goes on they become whitish.
Most of these abnormalities can be attributed to some of the following causes :
–
Poor physical conditions of the spawners.
–
Spawning late in the season,
–
Strong stimulation, that results in aborted eggs.
– Heavy concentrations of eggs for a long time on the bottom of the containers
before counting or adding the sperm, resulting in oxygen depletion.
–
Delay in adding the sperm.
–
Careless handling when cleavage Starts.
–
Overcrowded incubation.
–
High temperatures while incubating.
–
Polyspermy.
As the abnormal larvae do not grow, or their growth rate is slow, they car. be
discarded after a few days of culture for the appropriate sieving methods.
2.4. Larval culture
As we mentioned earlier, when trochophore larvae held in the incubation
containers become veliger larvae, the water in the tanks is filtered through a mesh and
the retained veliger are counted and placed in the tanks used for larval culture.
The early veliger or straight-hinge larvae have a D-shaped shell covering all the
soft body parts. The most conspicuous larval organ at this stage is the velum, heavily
ciliated, used for swimming and feeding. As larvae grow older a more or less prominent
umbo develops, and later on a ciliated and retractile foot, with a byssus gland. Some
species show an eye spot, whose presence announces that settlement can be expected
soon.
2.4.1. External factors affecting the larval growth
The larval growth rate is a useful index of the culture quality, and usually, the
faster the growth is, the better the survival and the higher the settlement rate will be.
There are several factors influencing the growth rate. Some of them, such as
quality and quantity of food, temperature, salinity and larval density, can be easily
controlled, but other factors like water quality or diseases cannot.
Food
For many years, one of the biggest problems related to larval culture was their
food identification. Later on, it was discovered that larvae feed on unicellular algae, the
only satisfactory food known to date.
As a consequence, a considerable amount of algal species have been isolated
and cultured, to determine its food value.
Some conditions are required for a species considered a good food source :
–
The size, 2 - 10 μm being the most advisable.
– Digestibility. In this sense, the presence and thickness of the cellular wall is
an important factor.
–
Toxic metabolites are produced by some algae, discarding them as food.
–
Factors such as easy culture and high yield are also important,
– The alga must fulfill the larvae requirements in carbohydrates, proteins, lipids
and vitamins.
–
Mobility is not essential, but advisable.
As a rule, mixed food results in a improved growth rate. The sinergical effect can
be ascribed to a more complete fulfilment of nutritional requirements.
The food ration, that is, the number of algal cells used for feeding the larvae,
regardless of larval density or size, will depend on the algal size.
The most commonly employed ration is the equivalent volume of 100 cells of
lsochrysis galbana per microlitre.
The food value of a species can change according to age, and even a good
species can become toxic owing to bacterial growth.
The most useful species are the following :
lsochrysis galbana
Pavlova (Monochrysis) lutheri Tetraselmis suecica
Phaeodactylum tricornutum
Pseudoisochrysis paradoxa
Thalassiosira pseudonana (ex : Cyclotella nana)
Chaetoceros calcitrans
Skeletonema costatum
lsochrysis tahiti
Rhodomonas baltica
Temperature
Usually considered to be the most important factor in larval growth rate. Most of
the species living in temperature waters increase their larval growth rate when the
temperature rises, but when the temperature is some point above 30° C, survival and
growth decreases sharply.
Salinity
As most of the cultured species live in estuarine habitats, it could be suspected
that salinity would not affect the larval growth rate excessively, as the larvae may be
exposed to fluctuating salinities in the environnement. In fact, they can withstand a
relatively wide range of salinity, and there is some evidence that animals living in more
estuarine habitats have a broader margin of tolerance for lowered salinities. For
example. Ostrea edulis has its lower limit at 20 °/oo (DAVIS & ANSELL, 1962), and
Crassostrea virginica at about 1O - 12.5°/oo depending on the salinity in the area where
the parents were living (LOOSANOFF & DAVIS, 1963).
Density of larvae
This factor is related to the larval size. However/ there is a wide range of
acceptable densities, the growth rate decreasing as density increases. A good growth
rate can be achieved at the following densities (CHANLEY, 1975):
Larval size
50 - 100 / μm
100 - 200 / μm
200 - 300 / μm
+ 300 / μm
Number/m|
15
8
5
1
The decreased growth rate in crowded cultures is supposedly due to
accumulation and to an increased rate of collision between larvae. The lack of food can
also affect the growth. However, an increased feeding rate can inversely affect the
growth rate.
Water quality
The water quality is a problem that is always present when rearing small animals.
The high surface-volume ratio of the larvae, and their forced exposition to any material
present in the water make them extremely succeptible to toxic or disease producing
agents (CULLINEY et al., 1975).
Periodically, the sea-water has a harmful effect en the larvae. However, in spite
of the importance of this subject, very little information is available on this subject, and
failures in growing larvae have been attributed to dinoflagellate blooms, high levels of silt
suspension, heavy metals and unidentified filterable components.
As a precaution, and before setting up a hatchery, some environmental
considerations must be kept in mind, in order to prevent water quality problems as much
as possible :
–
Salinity variations
–
Particle matter, and related to this subject, depth and exposure
of the shore.
–
Pollution.
–
Red tides.
2.4.2 Methods of culture
The volume of the containers where larvae are going to be cultured can range
from one to several hundred litres.
The culture can be performed in a open-to-flow or a stagnant system, the latter
being the most common. In this case, water is changed periodically, usually every other
day. Water changes on Monday, Wednesday and Friday is a pattern employed very
often.
The water can be either drained through a bottom valve, the larvae and detritus
being retained and sieved on filters of suitable size placed underneath or siphoned out
by means of a flexible pipe. In this case, either a mesh can be placed in the inner tip of
the pipe, preventing the larvae from draining, or the larvae are drained away and
retained on sieves in a similar way as when bottom valves are used. The latter system
allows us to reject dead or moribund larvae and detritus accumulated on the bottom.
After emptying, the containers must be carefully and thoroughly cleaned, by
means of hot fresh water and a non toxic detergent, and then rinsed two-three times with
filtered sea water before refilling.
The sieves holding the larvae must be placed in containers filled with filtered sea
water before putting them back into the larval culture tanks, and a microcospical survey
should be made of a sample picked up by means of a PASTEUR pipette for measuring
and controlling.
If necessary, selective sieving should be done to remove slow growers or dead
shells. After refilling the larval containers, the larvae are replaced inside, and then food
and antibiotics (if any) are added. However, as larvae grow older it may be necessary to
feed them daily.
Usually, a gentle aeration is supplied.
2.5. Settlement
The larval pelagic period ends when the animal settles. Before settlement there
are some changes in the larval behaviour. The larva ready to settle swims with its foot
protruding and when it touches some solid surface, the velum is retracted and the larva
crawls using the foot.
This behaviour can change suddenly, the foot being retracted, the velum
expanded and the swimming restarted.
When the oyster is ready to settle, after crawling and looking for a suitable
substrate, the shell twists and with the left valve facing the substrate, it attaches itself
definitively using the cementing substance of the byssal gland.
However, most of the molluscs settle temporarly by means of filamentous
byssus.
Morphological changes from larval to juvenile (metamorphosis,) start
immediately, involving the disappearance of some larval organs (velum) and the
development of new ones.
Size at settlement
Variable according the species. Usually, between 220 and 320 / μm.
Timing of settlement
Again variable according to the species. Heavily influenced by external factors.
Usually, Ostrea edulis requires 7-14 days, Venerupis spp about 3 weeks and Pecten
maximus 4 weeks.
Probably this is the most critical phase in larval cultures, as by this time it is
normal for larvae to crowd together in a sticky mess of mature crawling larvae, younger
swimming larvae, dead shells, faeces, food and detritus.
When arriving at this phase suitable sieving should be done, selecting different
development stages by size, and placing them according to their size in different
containers.
2. 5. 2. Settlement techniques
As we said before when settlement is on the point of happening, it is advisable to
separate the different sized larvae. The smaller ones will take longer to settle, so they
are put back into the larval culture containers, whereas the biggest ones will be ready to
settle, so they will be placed in settlement tanks.
We must consider that most of the commercially important species settle in a
temporary way whereas oysters settle definitively. Again, refering to oysters we can work
on cultch or cultchless spat.
The species attaching themselves temporarily do not need any collector, as they
settle on the bottom or walls of the settlement containers, from which they can be
detached easily, when necessary, by applying a jet of water. However, some filament
made coliectors can be used for some species like Pecten.
Two main systems are used for oysters : small particles or some kind of tiles or
stripping methods. The last technique may or may not involve a detachment a few hours
later or when oysters reach a certain size, meanwhile the use of small particles (200 350/ μm) enables us to get oysters without any removing techniques.
Settlement of some species like oyster can be hastened by adding adult oyster
extract to the substrate.
2.6. Nursery
Hatchery produced bivalve seed must be grown in a nursery prior to planting or
sowing. Small seed planted directly in the sea may suffer high mortalities owing to
predators, silting, clogging, adverse weather, etc...
Advisable size of transfer seed to the sea will depend on areas, species and
ongrowing techniques.
The aim is to grow the seed, until it reaches a suitable size for planting, as fast as
possible, to reduce the expenses involved in feeding, heating and handling but bearing
in mind that some seasons are not adequate for planting.
In the last years there have been some improvements in the nursery systems,
and the old style tray rearing has been changed to upwelling columns. This system
consists of forcing a water rich in phytoplankton through a mesh-made bottom container
where the seed is held.
Before placing the seed on the upwelling column, the following operations are
suggested :
When dealing with animals settling temporarily, change the water every other
day. After emptying the settlement containers, a very soft water jet is used just to rinse
the bottom and walls. In this way, only the settled spat will remain, attached on the
container surfaces. The outflowing water will be passed through a mesh, and the
retained larvae inspected, in order to determine if they will be recultured again or not.
The byssus-bearing remaining spat will be removed applying a strong water jet, retained
on a suitable mesh and placed in the upwelling columns.
– If we are dealing with oysters, we shall remember that two different
techniques can be used :
•
If a stripping method is employed, just allow the oyster to grow until the
required size, and then remove the spat. Next, place them in the upwelling column. This
system can damage the spat when detached.
•
If oysters are settling on particles, allow them to grow until a size big enough
to be sieved is reached. Then sieve, separating the oyster from the particles where
settlement did not occur, and place the oysters in the upwelling column.
The use of upwelling columns implies a control of water flow, a number of spat
per container and food ration. As these factors are related with size, as the spat grow
they must be changed, decreasing the density of spat and increasing the flow and food
ration.
WILSON (1981) suggests a minimum water flow of 1 litre per minute per 10 g of
spat, and a maximum standing biomass of 200 mg spat per litre.
Some experiments (URBAN et al., 1983) showed the best growth at the highest
food ration tested, an algal dry weight equivalent to 5 % oyster live weight.
The increasing food demands of the growing spat becomes a bottle-neck in the
culture of molluscs.
2.7. Algal culture
A hatchery requires big volumes of cultured algae, and high cell counts. There
are two main ways for culturing algae : monospecific cultures or bloom induced cultures
of mixed species. The last one is not advisable for larval feeding, as the mixed species
do not always fulfil the larval requirements, and bacterial growth can lead to heavy
mortalities. However, it can be the best technique for feeding spat.
There are Five major parameters which regulate algal growth : light, pH,
temperature, nutrients and turbulence, and they must be controlled when culturing algae.
The monospecific culture involves several scaling up levels. In our lab. they are
as follows :
–
Vial. Primary stock. Obtained from biological laboratories.
– ERLENMEYER flasks, 250 ml. Stock. Plankton perpetuation performed in
these stock containers. After a 7 day period of growth they are used for inoculating 6
litres carboys. No aeration.
– 6 litres carboys. Used for larval feeding and for inoculation of
bigger volumes. They are harvested after 5-15 days.
–
100 and 1 000 l tanks. For conditioning and spat feeding. Harvest partial.
2.8. Water processing
Prior to use, sea water must be filtered. The shema below shows the processing
we use in our laboratory :
As a rule, sea water must always be filtered, to remove unwanted organisms.
After filtering, some authors recommend also sterilizing it, using, for example, U.V..
Indeed, the larvae may be cultured without sterilizing the water, but in order to get a
better survival, a higher guarantee can be achieved by using U. V. sterilized sea water,
its use being an effective measure to prevent fungal or bacterial diseases.
When a volume of water is kept stagnant, the number of bacteria increases ; so,
the larval culture techniques promote bacterial proliferation, sometimes leading to a
complete larval mortality. Actually, the sporadic appearance of massive mortalities in
hatcheries are not uncommon, and usually they are produced by pathogenic bacteria.
The main source of bacterial contamination is due to the algal cultures (PRIEUR &
CARAVAL, 1979).
TUBIASH (1975) describes a very common disease, the baciliary necrosis,
whose agent is a Vibrio, destroying the cultures in a few hours.
The use of filtered and U.V. sterilized sea water, together with carefull cleaning
sometimes are not sufficient measures, and some authors recommend the use of
antibiotics. Usually, they are employed in a preventive way, owing to the fulminant
mortalities produced by pathogenic bacteria, rendering the treatment impossible when
the first symptoms appear.
Sanitation is the most important rule to adopt.
Table I : Results from the stimulation experiments carried on Venerupis pullastra
Stimulation Temperature Number of experiment Number of experiment
showing positive
responses
%
Number of shells
stimulated
Number of positive
responses
%
28 - 30° C
8
1
12,5
162
16
9,9
23 - 26° C
12
7
58,3
173
43
24,9
18 - 21° C
11
6
54,5
190
43
22,6
Results obtained with Venerupis decussatus
Stimulation Temperature Number of experiment Number of experiment
showing ositive
responses
%
Number of shells
stimulated
Number of positive
responses
%
23 - 24° C
4
0
0
65
0
0
28 - 29° C
8
8
100
194
68
35
Table II : Milligrammes of organic material in 108 cells
Chaetoceros calcitrans
1,15 ±
0,39
Isochrysis galbana
2,45 ±
0,81
Monochrysis lutheri
2,72 ±
0,60
Skeletonema costatum
4,04 ±
1,15
Phaeodactylum tricornutum
4,88 ±
1,36
Rhodomonas baltica . ..
7,09±
1,10
16,23 ±
4,47
Tetraselmis suecica
TABLE III
Effect of different foods on growth rate of the larvae of Pecten maximus. All the values are compared with a mixture of I.galbana +
M.lutheri, and this food is considered to be equal to 100.
Algal
Species
Growth
Sk
Ph
Rh
I+M+Rh+Ph
Rh+Ph
I+M+Ph
I+M
I+M+Rh
I+M+Ch
I+M+Rh+Ch
24.8
49.6
70.8
73.4
82.5
82.8
100
100.3
139.8
186.1
Sk = Skeletonema costatum; Ph = Phaeodactylum tricornutum; Rh = Rhodomonas baltica; I = Isochrysis galbana;
M = Monochrysis lutheri; Ch = Chaetoceros calcitrans
Fig. 1. Diagram of the conditioning system.
Fig. 2 - Days of conditioning
Fig. 3 - Larval growth of V. pullastra which were fed different
concentrations of M. lutheri
A. 100 cells/microliter
B. 75 cells/microliter
C. 50 cells/microliter
D. 25 cells/microliter
Fig. 4 - Slope of the growth curve of V. pullastra larvae reared at different
temperatures
Fig. 5 - Larvae growth of V. pullastra reared at different densities
A..
1 500 larvae/l
B.
3 000 larvae/l
C.
6 000 larvae/l
Fig. 6 - Larvae growth of V. pullastra reared at different densities
A. 10,000 larvae/l - Straight line equation Y = 94.77 + 6.11 x : r2 = 0.99
B. 20,000 larvae/l - Straight line equation Y = 101.41 + 4.80 x : r2 = 0,99
C. 40,000 larvae/l - Straight line equation Y = 109,94 + 2.70 x : r2 = 0,90
Fig. 7 – a – Effect of two monoalgal diets and b - Effect of the density of the spat culture on
a mixture of both on the growth of the
the weight increase (mg) and size (μm)
larvae (spat)
Fig. 7 - First fattening systems
a) Rearing cages
b) “Ipwelling” columna flows
Evacuation towards
the sewage outlet or
recycling
Fig. 8 - Straight regression line between the slope of the growth line Y and the
logarithm of the larvae concentration in culture,
V. decussata (a), V. pullastra (b)
a) Straight line equation : Y = 20.15 - 3.38 x : r2 = 0.94
b) Straight line equation : Y = 25.68 - 4.99 x : r2 = 0.91
Fig. 9 - Growth curves of Pecten maximus larvae, before and after their separation into two groups of different
growth rate.
a) Average growth of Monochrysis lutheri in erlenmeyers of 250 cc.
b) Average growth of Tetraselmis suecica in erlenmeyers of 250 cc.
c) Average growth of Isochrysis galbana in erlenmeyers of 250 cc.
- Average growth of algae cultivated in 6 1 recipients
a) Ph. tricornutum : b) Ch. calcitrans ;
c) S. costatum ; d) Rh. baltica.
- Average growth of three algae cultivated in 6 1 recipients.
a) M. lutheri ; b) I. galbana ; c) I. suecica.
Fig. 11 - Algae growth in 6 1. recipients. (PERES et al., 1977)
REFERENCES
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Pecten and other pelecypod mo Musks. Trans; Conn. Acad. Sci. 36 :
673 - 700.
CHANLEY, P. 1975- Laboratory cultivation of assorted bivalve mollusks, P 297 - 318 in W.L. SMITH & M.H. CHANLEY (edt) : Culture of marine invertebrate
animals, Plenum Press, N.Y.
CULLINEY, J.L., P.J. BOYLE & R.D. TURNER, 1975. New approaches and techniques
for studying bivalve larvae, p 257 - 271. In W.L. SMITH & M.H. CHANLEY
(edt) : Culture of marine invertebrate animals. Plenum Press. N. Y.
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oyster Ostrea edulis at lowered salinities. Blol, Bull., 122 : 33 – 39.
DUPUY, J.L., N.T. WINDSOR & C.E. SUTTON, 1977. Manual for design and operation
of an oyster seed hatchery for the American oyster Crassostrea virginica.
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FLASSCH, J.P., Y. KOIKE & C. AVELINE, 1973. Production de naissain de bivalves à
moyenne èchelle : but, perspectives. Colloque sur l'aquaculture, 22 24
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REYSS.
GONZALEZ, G & G. ROMAN, 1983. Larval culture of the scallop (Pecten maximus). 4th
international Pectinid Workshop, ABERDEEN, Scotland, May 1983. 10 p.
Mimeo
HELM, M.M., D.L. HOLLAND & R.R. STEPHENSON, 1973. The effect of supplementary
algal feeding of a hatchery breeding stock of Ostrea edulis on larval
vigour. J. mar. biol. Assu. U. K., 53 : 673 - 684
IMAI, T. 1966. Mass production of molluscs by means of rearing the larvae in tanks. 7th
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LE PENNEC, M. 1981. Les méthodes expérimentales induisant la ponte chez les
mollusques bivalve marins. Haliotis, 11 : 139 - 155
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(edt) : Advances in Marine Biology, Vol. 1. pp 1 - 136. Academic Press
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PEREZ CAMACHO, A., G. ROMAN & M. TORRE, 1977. Experiencias en cultivos de
larvas de tres especies de moluscos bivalvos : Venerupis pullastra
(Montagu), Venerupis decussata (Linnaeus) y Ostrea edulis (Linnaeus).
Bol.Inst. Esp. Ocean., 235 : 7-62.
PRIEUR, D. & J.P. CARVAL, 1979. Bacteriological and physico-chemical analysis in a
bivalve hatchery : techniques and preliminary results. Aquaculture, 17:
359 - 374.
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(L) en laboratorio. Bol. Inst. Esp. Oceano. N° 223 : 17 p.
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Culture of marine invertebrate animals. W-L. SMITH & M.H. CHANLEY
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and growth efficiency of juveniles of Crassostrea virginica (Gmelin). Jour.
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8. Artificial propagation
C. E. NASH & R. M. KONINGSBERGER
History of mullet culture
Farming of the Mugilidae has been practised for centuries but generally the cultivation of
this potentially invaluable source of animal protein for man has been small and nonintensive. Subsistence farming has been a tradition in the Mediterranean region, southeast Asia, Taiwan, Japan and Hawaii within fenced lagoons, creeks and swamps, and in
man-made ponds.
Experimental work in intensive mullet culture, aimed at finding ways to optimize
production which is a necessary forerunner of any large scale operation, is more recent.
This increased effort has developed in approaches differing from region to region
because of traditional needs and practices.
In the Mediterranean region, especially in Italy, the traditional valliculture
methods employed in raising mullet are now advanced (D'Ancona, 1955; De Angelis,
1969). In Egypt a successful stocking experiment was carried out at Lake Qarun in 1921
(Faouzi, 1936) using Mugil cephalus and Mugil capito. No effort was made to optimize
growth of the transplanted juveniles by supplemental feeding. A second transplanatation
was made of M. cephalus, M. capito and Mugil saliens. The latter was reported to spawn
successfully in the lake, but the slock of the other two species had to be replenished with
juveniles from the estuaries (El-Zarka, 1968).
In the Soviet Union, experiments with mullet were carried out in the regions of the
Black Sea and the Caspian Sea. In 1930 and 1934 M. cephalus, Liza saliens, and L.
auratus were introduced into the Caspian Sea (Thomson, 1966). The transplantation of
L. saliens and L. auratus was successful and their acclimatization, development and
reproduction were studied in later years (Perceva-Ostroumova, 1951; Babaian, 1958).
The work was followed by suggestions for further improvements in the region (Babaian,
1960; Chepurnov & Dmitriyev, 1962) and Apyekin & Tronina (1972) subsequently
published the tentative results of experiments on the stimulation of the maturing and
spawning of M. cephalus, M. saliens and Mugil auratus.
The mullet were introduced for a seconary crop in carp ponds in Israel in the
1950s (Perlmutter, Bograd & Pruginin, 1957; Pruginin & Kitai. 1957). Considerable
research work was then performed on artificial feeding in ponds (Erman, 1958),
seasonal and regional variations in the spawning season (Abraham, Blanc & Yashouv,
1966), histological studies of ovarian development in captivity (Abraham, Blanc &
Yashouv, 1968), culture at different stock densities (Yashouv, 1966), and breeding and
growth in captivity {Yashouv & Ben-Shachar, 1967).
In south-east Asia and the Far East efforts to intensify mullet culture were
centred in Taiwan, India and Hong Kong. Farming of mullet was also practised in Japan,
the Philippines, Indonesia and mainland China, but only as a seconary crop in the
culture of other species. Research in these countries has been sporadic. There are two
incidences of mullet rearing experiments in Japan. Between 1906 and 1909 at the Aichi
Prefecture Fisheries Experiment Station feeding experiments with mullet juveniles were
conducted and these were repeated forty years later (Tamura; 1966).
In the Philippines the possibility of raising mullet juveniles together with milkfish
in the brackish-water ponds was first suggested by Adams, Montalban & Martin (1931).
Although mullet were raised successfully with the milkfish for some time, a scientifically
supervised rearing experiment was not conducted until 1953 (Blanco & Acosta. 1958).
Polyculture of mullet with milkfish and carp was again proposed but has yet to be
intensified. In 1971 preliminary experiments on induced spawning of Mugil dussumieri
were carried out at the Marjan Sabalo Hatchery Experimental Station (Angelos, 1971)
indicating that research on intensive mullet culture in the Philippines had not been
abandoned.
In Hong Kong intensive culture of mullet was imposed successfully on the
traditional practice of carp culture (Bromhall, 1954). The culturing method developed
empirically used two pond systems stocked with M. cephalus as both the primary and
the secondary crop (Lin, 1940). The ponds were fertilized with organic matter and the
fish given artificial food. Culling started when the fish were about seven months old.
Chow (1958) conducted growth studies on pond reared mullet and found that their
growth rate compared favourably with that of natural stocks.
In India, with its extensive estuarine waters in Kerala, Bengal and Madras, mullet
have been farmed from very ancient times. Research in intensive culture began in the
1920s when rearing experiments with young mullet were conducted in Madras at the
Fisheries Department farm at Ippur (Campbell, 1921; Hornell, 1922) and at the
Chingulpet Fort moat fish farm (Gravely, 1929). In the 1940s two further aspects were
emphasized, namely studying the feasibility of acclimating mullet juveniles to fresh
water, and developing practices in polyculture. The first acclimation experiments were
undertaken in Madras with Mugil troschelli and Mugil wagiensis (Devanesan & Chacko,
1943; Job & Chacko, 1947). This was followed by acclimatization studies of Mugil parsia
in Bengal (Mookerjee, Ganguly & Sircar, 1946) and of M. cephalus and Mugil seheli in
Madras (Ganapati & Alikunhi, 1949).
Several other reports on existing farming practices with their problems were
published at the time. Improvements for the brackish-water farming of mullet in the
Ganges delta were suggested (Hora & Nair, 1944). Basu (1946) advanced the
adaptation of Chinese and Philippine practices for Bengal farms, and Pillay (1947)
published his extensive examination of culture in Bengal, Madras and Kerala. The
acclimation experiments led Panikkar (1951) to suggest that temperature and salinity
tolerances of the mullet species be studied in detail, but little appeared in the literature
until the report of Mohanty(!973). He recorded that juveniles of M. cephalus acclimated
to fresh water were more tolerant of changes in conditions and that tolerance varied with
length.
The most significant development in India has been the undertaking recently of
the artificial propagation studies at Kerala. Ovulation but not fertilization was achieved
with M. cephalus (Sebastian & Nair, 1973). However successful spawning and larval
rearing were achieved by Sebastian and Nair (1974) with Mugil macrolepis.
Although the pond culture of Mugilidae is not practised on a large scale in Korea,
the grey mullet is one of the important food fishes in its south-west region. One instance
of research deserves mention. Yang & Kim (1962) described an experiment to obtain
and hatch eggs of the grey mullet and to rear the larvae, but the work does not seem to
have been continued.
In Taiwan, at about the same time, the knowledge gained from centuries of pond
culture was utilized to begin an intensive programme on mullet culture. About 39 % of
the commercial catch of M. cephalus consisted of pond reared fish, cultured in
combination with carp in fresh-water ponds and with milkfish in brackish-water ponds.
Tang (1964) estimated that ten million juveniles were required to support the pond
culture of mullet each year. He pioneered work on the induced spawning of M. cephalus
as he knew that these resources were not infinite.
In 1966 a comprehensive research programme was established at the Taiwan
Fishery Research Institute for intensive culture and mass propagation of juveniles. In
subsequent years the techniques of induced spawning of mature fish caught during their
seasonal migration were refined and improved, and survival of the larvae extended to
thirty days. In 1973 the larval survival had increased to 19.35% and the production of
juveniles had been established. A summary of a decade of work at the Institute has been
made by Liao (1974).
In the United States the earliest mention of mullet farming was made by the US
Fish and Wildlife Service (Anon., 1940) and attributed to Prytherch. A general article by
Sharpe (1945) about the same farm quoted a yield of 5000 lb of fish per acre. Hiatt
(1944) obtained information on the role of mullet in the food cycle of Hawaiian fish
ponds. Lunz (1951) described preliminary experiments of mullet culture in brackishwater ponds in South Carolina. In Florida an experiment to raise the pompano,
Trachinotus carolinus, in-advertently resulted in a yield of which Mugil curema and M.
cephalus constituted the majority of fish (Johnson, 1954).
At present, experimental work with Mugilidae is centred in Hawaii, Texas and
Louisiana. In Hawaii, the Oceanic Foundation successfully achieved artificial spawning
of M. cephalus following induced breeding of captive broodstock (Shehadeh & Ellis,
1970; Shehadeh, Kuo & Milisen, 1973b). Larval rearing efforts met with mixed success
and individual survival figures (up to 25.5%) could not be guaranteed (Kuo, Shehadeh &
Milisen, 1973a; Nash, Kuo & McConnell, 1974). In Texas mullet were raised successfully
in ponds receiving the heated effluent from a power plant (Linder, Strawn &. Luebke,
1974), and in Louisiana acclimatization experiments were conducted with mullet
juveniles (Shireman, 1974).
From this brief historical survey it is evident that the direction of the experimental
research and development for the culture of the Mugilidae has, of necessity, been
toward induced spawning and larval rearing. For centuries the farming of mullet, as with
other species, has depended on natural resources for the annual replenishment of stock.
However the annual spawning migrations of the adults and the strength of the yearclasses are all subject to environmental biological factors about which there is little
agreement on importance. Present evidence indicates that these factors differ with
locality, region and even between populations within the species. The natural availability
of juveniles is therefore subject to unpredictable variations in occurrence and
abundance. More importantly the juveniles are collected in those coastal and estuarine
waters where pollution is threatening or in some cases has already changed the
ecosystem. The future availability of resources in such waters is becoming increasingly
uncertain. Finally, improvement in fishing techniques, particularly for schooling fish on
their spawning migration, is affecting the natural population and hence their progeny.
The literature is full of reasons for the depletion of natural populations and
weakening year-classes. Yet there is an anomaly for the proponents of culture.
Commercial fishermen consider that too many juveniles are removed by pond fishermen
thus depleting the resources of the natural fishery. Consequently limits have been
imposed on the number of juveniles of certain species which can be removed for
intensive culture.
The future of aquaculture is entirely dependent on the success of artificial
propagation and larval rearing. Juvenile resources have to be independent of the natural
population. Once this is achieved, then the benefits of genetics and selective breeding
will make aquaculture the parallel of intensive agriculture with its fast growing strains and
specialized breeds. When this occurs, the Mugilidae will really have an advantage over
all other species because of the number of related types which can be used to develop
particular farming strains for almost any region or specific location.
The need for an intensive effort in mass propagation has been summarized by
Oren (1971). He said In order to achieve maximum production of mullets under
controlled conditions, one of the axioms is a steady supply of fry independent of
conditions in the natural environment, natural spawning and migration of fry inshore.
Only when such a supply is available will the mosteconomic and most efficient way of
utilization of the mullet, as a consumer of the first trophic level, be channelled for the
benefit of man.’
Adult broodstock
The success of an artificial propagation system for any plant or animal species depends
primarily on the quality and quantity of broodstock resources. Large numbers of sexually
mature individuals must be contained in good health under acceptable environmental
conditions in order to reproduce and yield viable offspring. Some essential external
conditions for broodstock fish are suitable water quality, a nutritious diet, a high standard
of hygiene and limited physical disturbance. But of most importance the broodstock must
be exposed to the correct environmental parameters which influence the physiological
changes in the pituitary gland and stimulate the gonads to seasonal maturity.
The endocrine system of all vertebrates forms the main link between the
reproductive organs and the environmental regulators. Rhythmic regulators such as
temperature and photoperiod, mediated through the central nervous system, initiate
neurosecretions which in turn regulate the activities of the pituitary gland. As one of
many target organs the gonads are influenced accordingly. The reproductive cycles are
thus regulated intimately by the trophic hormones of the pituitary.
Many experiments with fish have used gonad development to interpret the effects
of certain environmental regulators on the reproductive cycle. Among the factors
concerned temperature and photoperiod are the two most important which initiate
pituitary activity for fish in temperate and sub-temperate regions (Hoar, 1959). The
relative importance of each varies with different species of teleosts. Photoperiod has
been reported as the dominant factor influencing the reproductive cycle of Enneacanthus
obesus, Notropis bifrenatus and Fundulus confluentus (Harrington, 1959), Gasterosteus
aculeatus (Baggerman, 1957), Salvelinus fontinalis (Henderson, 1963) and Oryzias
latipes (Yoshioka, 1962). Temperature has been shown as dominant for Phoxinus laevis
(Bullough, 1940), Apeltes quadracus (Merriman & Schedl, 1941),Gambusia
affinis(Medlen, 1951)and Couesius plumbeus (Ahsan, 1966).
Henderson (1963) concluded for Salvelinus fontinalis that the influence of an
environmental regulator varied with the stage of gonad maturation. The period most
responsive to a regulator could also vary between males and females of the same
species, and the gametogenetic process may be independent of environmental
regulators at certain stages of maturity.
The reproductive cycle of most vertebrates is under the dual control of an internal
physiological rhythm and an external seasonal rhythm. The refractory period or resting
stage of the reproductive cycle is considered to be the time during which the two
rhythms coincide and reinforce each other. As the fish are exposed to changing
environmental conditions such as photoperiod and temperature the external rhythm
begins to dominate. Its influence on the reproductive processes is transmitted by
changes in the quantity of gonado-tropin released from the pituitary gland.
The physical containment and maintenance of adult grey mullet in the most
suitable conditions for survival are not difficult problems. The fish readily become
domesticated as testified by centuries of pond farming. They grow and are technically
mature, although the final stages of gametogenesis are not completed and no incidence
of total development and unassisted natural spawning in captivity has been recorded. At
present these need the artificial stimulus of hormone injection to complete the breeding
cycle.
In order to simulate the desirable environmental conditions for gameto-genesis of
captive broodstock, it is necessary to examine the conditions at locations where the grey
mullet spawn in nature.
Natural spawning locations
The natural spawning locations of grey mullet species, which have been described or
deduced by many workers throughout the world, do not indicate specific and similar
environmental patterns. The overall picture is confused both by misidentification of
generic types observed and the variety of facts on which the spawning record is being
made. For example, many reports are based on the collection of adult fish with ripe
gonads and usually loose eggs; others describe small numbers of eggs or larvae in
plankton tows and make predictions about the spawning location based on tidal
movement and stage of development of the samples. Some reports describe inshore
schooling and then a migration offshore, presumed to be for spawning; others describe
schooling inshore for spawning. The location of spawning grounds for the mullet can
only be described as controversial.
Anderson (1958) reviewed the records of many American workers who
suggested the time and place of spawning of Mugil cephalus along the South Atlantic
and Gulf coasts of the United States. From the evidence of collection of larvae and the
occurrence of juveniles on the coast from lower Florida to North Carolina, he believed
that the striped or grey mullet spawned offshore over a broad area extending from about
the 20 fathom line into the Gulf Stream. In contrast with the spawning of the silver mullet,
Mugil curema, which began in early spring when water temperatures were rising over the
continental shelf (Anderson, 1957), M. cephalus spawned during late fall or winter when
water temperatures were falling. Breder (1940) observed and described an aggregation
of adult fish in the shallow creeks of the Florida coast and believed that spawning was
taking place. Although he collected no eggs, his detailed description of the movements
of the males around the females compares exactly with the observed spawning
behaviour of mullet in aquaria, and it must be assumed that the fish were attempting to
spawn.
Broadhead (1953), Dekhnik (1953) and Arnold & Thompson (1958) provided
authenticated instances of M. cephalus spawning at sea in surface waters, but over
deep water (50 fathoms in the Black Sea, and 750 fathoms in the Gulk of Mexico). Fitch
(1972) described the capture of a ripe female over 40 miles off the Baja California coast.
Other more unusual spawning places have been suggested. Roughley (1916) believed
spawning to occur in fresh water. Smith (1935), Breder (1940), Jacob & Krishnamurthi
(1948) believed it took place in estuaries and tidal creeks, and Kesteven (1953) in the
coastal surf zone of Australian waters.
Demir (1971) reviewed the information available on spawning of grey mullets in
the North Atlantic. The spawning of Mugil labrosus was assumed to be during April in
British waters, as schools of adults were observed offshore and the juveniles entered
tidal pools on the Channel coast and in Southern Ireland in July and August. Kennedy &
Fitzmaurice (1969) believed the spawning period to last several weeks in Irish waters
with May as the peak spawning month. Hickling (1970), in his contribution to the natural
history of the English grey mullets, noted the spawning period of Crenimugil labrosus
from January to April and that one of its spawning locations was near the Isles of Scilly.
Two ripening Liza ramada he found in autumn indicated a late spawning season. He did
not find any Liza aurata with active gonads. Le Dantec (1955) noted that genital activity
for C. labrosus lasted from January through until April for fish in the Biscay region.
In the Mediterranean, Caspian and the Black Seas, the spawning periods again
varied from region to region, Yashouv & Berner-Samsonov (1970) produced an
extensive review of the spawning seasons of five species of Mugilidae in the Black Sea
and the Mediterranean. Hamis (1972) stated that the spawning areas of certain species
of mullet were those places where the optimum conditions for the young were available.
In the Black Sea, Mugil saliens spawned from late June to October, M. cephalus
spawned from late May to late October and M. auratus spawned from early June to early
November. In the Mediterranean the spawning of M. saliens took place between May
and October, M. cephalus from early May to September, M. auratus from early
September to late December, L. ramada from early October to late December, and M.
labrosus from early December to early April.
Avanesov (1972) established that spawning of the grey mullet in the Caspian
Sea occurred in a wide area beginning in the southern part at the end of May and
extending northward. He recorded the most intensive spawning in the Turkmenian
waters in the south in August, at a temperature of 25-29°C and about seven miles
offshore where the depth was 5-40 m. Spawning of the long-finned mullet he noted
occurred later at a considerable distance offshore where depths were over 400 m.
Wimpenny & Faouzi (1935) first recorded the shoaling migrations of M. cephalus
and M. capito during the spawning period. The schools moving from the Delta Lakes of
Egypt to the sea were entirely composed of spawning fish. Thong (1969) observed
migrations of Mugil auratus, M. labrosus and M. ramada during egg laying from the
coastal regions of NW. France into the open sea.
In the Pacific and Indian Oceans little information on spawning of Mugilidae is
available except for M. cephalus which spawns in late winter in the tropics and
subtropics. Some summer spawners were recorded by Sarojini (1958). In tropical Bengal
waters Liza parsia spawned between January and March, and Liza cunnesius from May
onward and in the time of the monsoon. Kurian (1974) recorded the maturity of mullet in
the ponds and lagoons of the Indian coast. He noted the different types of spawning
migrations of M. cephalus, M. tade and Liza macrolepis, but all were seaward or near to
the estuaries.
Wallace (1974) recorded the distribution of M. cephalus in the high saline lake
system of St Lucia on the east coast of South Africa. He observed two seaward
migrations in response to the changing hydrological and topographic features of the
water system. No spawning was recorded in the lakes. Cervigón & Padrón (1974)
observed M. curema in the high saline lagoons along the coast of Venezuela. They
concluded that no spawning occurred in the lagoons but the adults migrated to the open
sea and possibly for two spawning periods a year. Table 8.1 summarizes the spawning
seasons of Mugilidae.
The records deducing the spawning locations from the numbers of eggs and
larvae in plankton samples make no reference to the time of day at which spawning
might occur. The observations of Deknik (1953) and Arnold & Thompson (1958)
indicated that M. cephalus spawned at night at the water surface but over considerable
depth. Anderson (1957) reported night spawning of M. curema.
Although much reference is made to water depth and location of spawning sites
offshore, no workers report that the fish themselves descend deep to spawn. Hotta
(1955) recorded very small larvae of M. cephalus in plankton tows from 100 fathoms
deep near Japan, and Zviagina (1961) found eggs of Liza haematocheila deep in Peter
the Great Bay.
The incidences of mullet eggs and larvae being taken in plankton tows are few.
Demir (1971) recorded the occurrence of postlarvae of M. auratus and M. labrosus in
British waters for the first time. Previously the eggs and larval stages of Mugil labrosus
had only been recorded once by Sanzo (1936), and the eggs only of Mugil auratus by
Sanzo (1931) and Vodyanitskii & Kazanova (1954). Although depth may not be
important for the adults at spawning it may be important for incubation and larval
development (pp. 281 and 289).
From histological examination of adults Stenger (1959) believed that M. cephalus
spawned more than once a year. Bromhall (1954), on the evidence of the size and
distribution of the juveniles, concluded that there were two periods of spawning in the
vicinity of Hong Kong with a lunar period apart. However it is generally assumed under
normal circumstances that most grey mullet species produce only one brood of eggs
each year, and that some females only spawn in alternate years after their first maturity
(Thomson, 1955).
Table 8.1. Spawning seasons of Mugilidae according to the literature
Apr.
Mugil saliens
May June July Aug. Sept. Oct.
Israel
Tunisia
Black sea
Venetian lagoons.
Nov. Dec
Israel
Tunisia
Mugil chelo
Crenimugil
labrosus
Jan. Feb. Mar.
British waters
British waters
Irish waters
Biscay region
Biscay region
NW
France
N
Adriatic
Mugil labrosus
NW France
Israel
Mugil auratus
Tunisia
Black Sea
Messina
Castellón
NW France
Israel
Tunisia
Mugil capito
NW France
Gulf of Mexico
Formosa
W Florida
E Florida. N Carolina
Israel
Mugil cephalus
Corsica
Tunisia
Egypt
Black Sea
Australia (winter)
N Adriatic
SW India
Hawaii
The references consulted were: Australia, Thomson (1963); Biscay region, Le Dantec (1955), Black Sea, Hamis
(1972); British waters. Hickling (1970); Castellon, Belloc (1938); Corsica. Belloc(1938); Egypt, Paget(l923); Florida east
coast North Carolina, Anderson (1958); Florida west coast. Broadhead (1953); Formosa, Tang (1964); Gulf of Mexico,
Arnold & Thompson (1958): Hawaii. Kuo & Nash (1975); Irish waters, Kennedy & Fitzmaurice (1969): Israel, Yashouv &
Berner-Samsonov (1970); Messina, Sanzo (1931); N Adriatic, Sanzo (1936); NW France. Thong (1969): SW India. Kurian
(!974); Tunisia. Heldt (1948); Venetian lagoons, Gandolfi & Orsini (1970).
In summary, from the extensive and conflicting data and the possible
misidentification by the observers, it is not possible to define a pattern in the
environmental conditions necessary for successful natural spawning. Hamis (1972) was
probably close to the truth when he stated that the spawning areas of certain species of
mullet were those places where the optimum conditions for the young were available.
More importantly, he should have included the optimum conditions for the incubation of
eggs.
Photoperiod and temperature rhythms time the onset of gametogenesis and
these rhythms, which differ from region to region throughout the world, influence the
indigenous population of mullet species. Existing data on the influence of salinity,
temperature and dissolved oxygen on the viability of the eggs of M. cephalus (see pp.
282-3) show that incubation and development occur to some degree within a wide range
of these parameters. The results also show that there are optimum conditions for both.
Environmental data on the temperature of the water during spawning of M.
cephalus indicates some adaptation from region to region, with temperatures recorded
between 12 and 24 °C. All records show a strong preference by the fish for oceanic
water as the medium for incubation, with salinities of 32-35‰. It is interesting to note the
observations of Wallace (V974) and Cervigón & Padrón (1974) for fish which lived in
hypersaline conditions but which migrated to normal oceanic salinities to spawn.
Kuo, Nash & Shehadeh, (1974b) demonstrated that environmental manipulation
of photoperiod and temperature increased the individual spawning frequency of adults,
and that the spawning season could be prolonged throughout the year. The
manipulations were all made in sea water of salinity 32‰. Their evidence indicated that
the spawning behaviour of the grey mullet species was not a strictly controlled and
regulated act. In fact the evidence pointed to a loosely controlled behavioral response.
Therefore the many controversial and apparently misleading observations on the
spawning period and location will be authentic for that respective population at that
specific time of year and in that particular region.
It is concluded that the adults move to spawn in the nearest location which will
provide the eggs and larvae with the highest chances for survival, specifically to oceanic
water of salinity of 32-35‰ but up to 39.5‰ for the eastern Mediterranean and 41‰ for
the northern Red Sea have been recorded. The distance of the migration may be short
or long, depending on the local conditions of topography and tidal movements. For
example, in Hawaii where there is no strong tidal movement but a coastal gyre, the
adults move offshore beyond the coastal reef a distance of one or two miles; in Australia
the fish move upcurrent many miles on both the west and east coasts before spawning,
so that the long natural drift will return the juveniles back to the home estuaries several
weeks later. Depth does not appear to be a vital factor for survival. Although the eggs
have a natural buoyancy and are capable of surviving great pressures and can be found
in deep water, the records do show that eggs and larvae develop predominantly in the
upper ocean layers.
Artificial spawning conditions
No record has been made of the Mugilidae spawning unaided in captivity or in artificial
conditions. Successful fertilization of hand stripped eggs and milt from adults caught at
sea has been claimed by Sanzo (1036) and Bollow (1038). Other successes have been
reported with fish matured in large ponds. The chances for this practice to become the
base of an artificial propagation unit are as yet too small to be considered further.
Reliable results have been obtained from fish matured in captivity or captured at sea but
induced to complete gametogenesis and spawn by the injection of hormones.
Suitable artificial conditions for holding the broodstock of grey mullet can only be
described as those enclosures which permit the female fish to develop their oocytes
beyond the tertiary yolk globule stage (stage III as described by Kuo et al., 1974b) and
the males to complete spermiogenesis. Without hormone stimulation females will not
mature to the ripe stage (stage IV) prior to ovulation, but will undergo atresia (stage V)
and degenerate.
The first report on the induced spawning of Mugil cephalus reared in captivity in
fresh water ponds was made by Yashouv (1969). Liao (1974) summarized the work in
Taiwan between 1963 and 1973 on the propagation of M. cephalus, using spawning fish
collected from the sea and from fish contained in large salt-water ponds. For the
broodstock the workers in Taiwan relied on strong uninjured male and female specimens
selected from the catches of commercial fishermen during the spawning run along the
southwest coast of Taiwan. The selected fish were placed in strong plastic bags filled
with sea water and inflated with oxygen. Most of the mullet caught were of the IV-year
class and measured about 32-50 cm in length and weighed 1.0-2.1 kg each. The
specimens were all sexually mature with well developed gonads, but the eggs of the
females were never fully ripe for natural spawning.
Pond stock were maintained in Taiwan in fresh water at first, with sea water
added slowly over a three-month period prior to spawning. The fish were fed a special
diet and also injected periodically with mullet pituitary glands and Synahorin. Pond
reared fish were easier to spawn than wild stock as they were more docile and free from
injury. Large tanks specially constructed for holding broodstock were made of concrete
and measured 5 x 7 x 1.5 m deep. Sea water was circulated through each and all were
aerated continuously.
Shehadeh, Kuo & Nash (1973c) established broodstocks of M. cephalus in small,
rubber-lined dirt ponds supplied with circulating sea water. In addition, the ponds
contained a substrate of weighted polyethylene strips which increased the internal
surface area and provided a stable supply of benthic diatoms, blue-green and
filamentous algae. Three-year old fish survived readily in such conditions and matured
the following year. They were then successfully induced to spawn by hormone injection.
The small ponds were excavated and lined with butyl rubber sheet (1 mm thick) and had
a volume of 26 m3. A food supplement was provided in addition to the available natural
growth.
Sebastian & Nair (1974) reported on the collection and holding of Mugil
macrolepis in preparation for spawning. Mature fish were taken from local brackish
waters in Chinese dip-nets and transported to small concrete tanks, 170 x 95 x 70 cm
deep. The gravid female fish were 13-23 cm in length and 40-130 g in weight. Water in
the tanks was changed intermittently.
Kuo et al. (1974b) described at length the holding of M. cephalus subjected to
environmental manipulations of temperature and photoperiod. The time of onset of
vitellogenesis was determined to be about eight weeks after exposure to a short
photoperiod regime (6 L/18 D) at temperatures ranging from 17 to 26 °C. The response
of oocyte development to the retarded photoperiod regime was consistent and unrelated
to any other preconditioning of photoperiod changes, including a simulated natural light
cycle. The data also indicated that development of the oocytes was accelerated by
constant exposure to a temperature of 17 °C and a 6 L/18 D photoperiod, but that it was
not completed as only limited yolk deposition occurred in the tertiary stage.
For M. cephalus, it is essential to maintain broodstock prior to spawning in full
saline conditions (32-35‰, and up to 39‰ for the eastern Mediterranean). There is also
evidence that the fish mature readily even after prolonged periods in captivity. Yashouv
(1969) reported some success working with M. cephalus in fresh water, but the work of
Hines & Yashouv (1971) on the increased activity of the spermatozoa of M. capito in sea
water together with the practical experience of others working with M. cephalus indicate
a preferential use of sea water for holding broodstock.
Ambient temperature and photoperiod conditions regulate the normal seasonal
maturation of captive stocks. But the feasibility of breeding through-out the year or
extending the breeding season by manipulation of the photoperiod and temperature
regimes has been proved and will produce greater use and increased efficiency of
propagation facilities.
Spawning behaviour and fertilization
Breder (1940) and Arnold & Thompson (1958) made some of the first
observations on the spawning behaviour of Mugil cephalus in nature. They observed
large numbers of fish schooling but scattered into small groups, generally made up of
one large female and a varying number of smaller and more active males. The groups
remained close together as if attached.
The induced spawning techniques developed by Shehadeh & Ellis (1970) and
Shehadeh et al. (1973b) permitted natural spawning behaviour following injection of
regulated doses of purified salmon pituitary gonadotropin. The final courtship and
spawning behaviour described by them was similar to that observed by the others many
years before.
As a consequence, for the final stages of the present induced breeding
techniques with natural spawning, two or three males are placed in an aquarium with
each recipient female about 2 h before spawning. A female will usually spawn some 12 h
after receiving the second and last injection. The males become more active as
hydration in the female progresses, indicated by distension of the belly and frequent
excretion of calcium deposits.
Spawning is heralded by a violent quivering of the males which are then lying
parallel to and facing the same way as the female and touching. The first release of a
small number of ripe eggs stimulates the males to liberate spermatozoa. The female
then responds with an explosive and continuous release of eggs.
Although male fish were once given exogenous hormone treatment to finalize
maturity the practice was found unnecessary for spawning in the natural breeding
season. If males are needed for spawning out of season then spermiation can be
induced readily by the injection of 17-alpha methyltesto-sterone (Shehadeh, Madden &
Dohl, 1972).
The effectiveness of the hypophysation technique for spawning depends
ultimately on the selection of suitable recipient fish at the proper stage of ovarian
development. For species of fish which undergo normal gonad development but fail to
spawn in captivity, identification of this stage is critical.
To date, selection of recipients has been largely subjective. External anatomical
characteristics have been described and used, e.g., depth and fullness of belly, colour
and state of swelling of the cloaca, softness and resilience of the belly, roughness of
pectoral fins or presence of head tubercules. More complex descriptions include the
microscopic appearance of oocytes (Sundararaj & Goswami, 1969), histological
structures of eggs (Chen, Chow & Sim, 1969), or other histological data. Other
physiological parameters associated with sexual maturity, such as elevated plasma
proteins and calcium concentration, have been used but are of little practical use.
Shehadeh, Kuo & Milisen (1973a) described a method for the assessment of ovarian
maturity in vivo, which was accurate and reliable and could replace all subjective
methods for Mugilidae.
Kuo, Nash & Shehadeh (1974a) described standard procedures developed and
applied regularly to induce spawning of M. cephalus under controlled conditions.
Methods for determination of the stages of egg development and required dosage of
partially purified salmon gonadotropin (SG-100) for spawning were illustrated and
emphasized so that the procedures could be readily used by other culturists. The
potency of the gonadotropin was described by Donaldson, Yamazaki, Dye & Philleo
(1972) as 1 mg equivalent to 2150 IU human chorionic gonadotropin (HCG).
Liao, Lu, Huang & Lin (1971), from experience gained spawning M. cephalus
freshly taken from coastal waters, recommended a first injection within 1 h after stocking
in the tanks and again within 24 h. The total dosage for each fish was 2.75-5 mullet
pituitary glands mixed with 20-50 Rabbit Units of Synahorin. Vitamin E was also injected
into the fish. The fish were later stripped and the eggs fertilized by the dry method after
careful observation for the correct spawning time. The best response was judged by
distension of the belly after about 10 h, a loose and soft belly, and finally the release of
'water eggs' particularly when the spawner was handled.
Anatomical characteristics are not always the most reliable indication of maturity,
particularly for fish held captive all year round. Many females with soft and enlarged
bellies can be in the early stage of oocyte development even during the natural breeding
season. Enlarged abdomens are often the result of engorged intestines and
accumulation of visceral fat.
Ovarian maturity, that is the stage of development of intra-ovarian oocytes, is
most accurately obtained by the method of Shehadeh et al. (1973a). Intra-ovarian
oocytes are removed in vivo from an unanaesthetized female through a polyethylene
cannula. The cannula is inserted into the oviduct for a distance of 6-7 cm from the
cloaca, and oocytes sucked orally into the tube by the operator as the cannula is
withdrawn. Oocyte samples from the mid-portion of the ovary are the most
representative and sampling error is minimized by avoiding the extremities.
The oocytes are removed from the cannula and washed and preserved in a
solution of 1 % formalin in 0.6 % sodium chloride solution. They are then placed on a
small 'Plexiglas' plate and measured with an ocular micrometer. Fine grooves cut in the
plate align the oocytes and facilitate measurement. Egg diameters are measured along
the horizontal axis and the measurements grouped into 50 μm class intervals. The
sexual maturity of the fish is expressed in terms of mean egg diameter, calculated from
the egg diameter frequency distribution.
The oocytes of M. cephalus develop in synchrony. Ovarian development
therefore is determined accurately and quickly without sacrificing female fish. The
method also provides a means to observe and record oocyte development in individual
fish and thus precludes variation between females in the broodstock. Furthermore it
replaces the need for any histological processing and examination of oocytes.
Eggs
Fecundity
Thomson (1963) reviewed a number of papers which reported the fecundity of Mugil
cephalus in terms of total egg numbers. He quoted estimates of 1.2-2.8 million eggs per
fish, Sebastian & Nair (1974) estimated the fecundity of Mugil macrolepis at 1.2-4.0
million eggs per fish depending on size. Hickling (1970) listed the fecundity of several
species of grey mullet as follows:
Species
Mugil cunnensis
AIdrachetta forsteri
Mugil parsia
Crenimugil labrosus
Liza ramada
Mugil cephalüs
Mugil cephalus
No. of eggs
(thousands/kg)
15-57
126--650
200-600
372-745
581-1243
1200-2800
3600-7200
Reference
After Sarojini (1958)
Thomson (1957)
Sarojini (1957)
Hickling (1970)
Uickling (I970)
Thomson (1963)
Nikolskii (1954)
Kuo, Shehadeh & Milisen (1973a) determined the fecundity of M. cephalus to be about
648 eggs/g body weight of three-year old fish. Nash et al. (1974) quoted 849 eggs/g for
older individuals. Liao, Cheng, Tseng, Lim, Hsieh & Chen (1972) reported 0.7-1.9
million/fish.
In Hawaii and Taiwan, where induced spawning of M. cephalus is regularly
performed, IV-group females weighing between 1 and 2 kg each are preferred for
breeding. Consequently over 1 million eggs per female fish are released for fertilization
following the induced hormone treatment.
Morphology and quality
The morphology of eggs before fertilization was described for several of the Mugilidae by
the early naturalists, most of whom made reference to the characteristic large oil globule.
The availability of eggs at all stages of development during the induced breeding
procedure has resulted in full descriptions for Mugil cephalus by Sanzo (1930), Tang
(1964), Yashouv (1969), Liao et al. (1971), Kuo et al. (1973a) and Tung (1973); by
Sanzo for M. chelo (1936) and M. labeo (1937); by Anderson (1957) for M. curema; by
Perceva-Ostroumova (1951) and Dekhnik (1954) for M. saliens.
Eggs of the Mugilidae are spherical and transparent. The surface of the egg shell
is smooth and unsculptured. The yolk appears unsegmented and there is predominantly
one large oil globule making the eggs extremely buoyant. The eggs are not adhesive
Eggs from M. cephalus and M. capito were observed by Yashouv & BernerSamsonov (1970) to have more than one oil globule and these subsequently developed
and hatched. During development they observed the droplets to merge. On hatching the
larvae had one oil globule (rarely two) located in the yolk sac.
Sanzo (1936) described eggs of M. chelo with one large and several smaller
globules, and Perceva-Ostroumova (1951) noted the same for M. saliens. Kuo et al
(1973a) stated that the frequency of multiple oil droplets in eggs of M. cephalus
increased with the manual pressure of artificial stripping. Spontaneous release of the
eggs by the females produced eggs with a single oil globule and Nash et al. (1974)
considered that to be normal and desirable. Although the small oil globules were
observed to coalesce during development the survival of eggs which initially contained
multiple oil droplets was always low.
Yashouv & Berner-Samsonov (1970), in an extensive contribution to the
knowledge of eggs and early larval stages of Mugilidae, reviewed data of egg and oil
globule diameters in samples from Mugil saliens, M. cephalus, M. capito, M. auratus and
M. chelo at a variety of locations. They included some data from the synopsis on M.
cephalus prepared by Thomson (1963). The comprehensive data revealed a wide range
of diameters reported for the same species in different locations.
Kuo et al. (1973a) reported the mean egg diameter of fertilized eggs of M.
cephalus as 930 μm, with a range of 880-980 μm. The single large oil globule had a
uniform diameter of 330 μm. Tung (1973) quoted a mean egg diameter of 0.89 mm for
the same species, and oil globule diameter of 0.39 mm. Nash et al. (1974) specified a
mean egg diameter of 0.93 mm.
A question posed by many workers culturing either Mugilidae or other species by
induced breeding is whether the quality of individual oocytes is inferior to those produced
in nature. Induced breeding does accelerate final development and therefore the egg
and subsequent embryo may be deficient in certain biochemical constituents necessary
for total development.
Bromhall (1954), Sarojini (1958), Erman (1961) and Hickling (1970) examined
the gonads of several species of mullet including M. cephalus and observed that their
state of development was often consistent with a seasonal production of more than one
batch of eggs, possibly within a period of a month. Kuo, Shehadeh & Nash (1973b)
demonstrated that M. cephalus could be induced to spawn more than once a year. It is
possible that artifically induced spawning, with its positive climax and total release of
oocytes from the ovary, may be an unnatural forced reaction impeding complete
development of the embryonic stages.
Little work has been accomplished on the biochemical composition of the
oocytes before and after spawning. Kuo (unpublished data) examined changes in the
biochemistry of eggs of M. cephalus during hydration and changes in mean egg
diameter, water content and osmolarity. He showed that both soluble (glucose) and
insoluble (glycogen) carbohydrates gradually decreased through hydration with a distinct
drop prior to spawning. Total lipids increased from 16 to 25%. The major polar lipid was
lethiein with decreasing amounts of phosphatidyl/ethanolamine and lysolecithin, plus
other unidentified trace components. The main nonpolar lipids were cholesteryl-esters
and triglycerides. The proportion of free fatty acids was small. Palmitoleic acid (C18:1),
palmitic acid (C18:0) and oleic acid (C18:1) were the major fatty acids, with decreasing
amounts of myristic acid (C18:0), linoleic acid (C18:2) and some higher fatty acids
containing 20, 22 and 24 carbon atoms. He recorded a conspicuous increase in the
amount of soluble nitrogen-containing ninhydrin compounds. There was a general
increase in amino acids particularly the neutral ones such as alamine, serine, leucine
and isoleucine. There was some change in the level of total protein but less pronounced
than that of the soluble nitrogen containing compounds.
Kuo (unpublished) also showed the pre-ovulatory eggs were isotonic with sea
water and the ovulatory eggs became hypotonic due to the rapid intake of external water
during hydration. In the 4 h postovulatory period a remarkable increase in the osmolarity
adjusted the osmotic pressure from hypotonic to isotonic to sea water at the time of
spawning. A change of the main individual electrolytes sodium, potassium, calcium and
magnesium ions was found variable due to the increase in water content. No
comparable data exist for the analysis of eggs from M. cephalus developing naturally
without induced treatment.
Although the need to identify the biochemical composition of normal eggs of
Mugilidae still exists, artificial propagation of certain species following induced breeding
has been reasonably successful in Taiwan, Hawaii, Israel and India. It is improbable that
the quality of eggs produced by external hormone stimulation is inferior. The failure of
the larvae to survive in large numbers is probably due to subsequent mishandling
because of poor techniques.
Behaviour
The vertical migratory behaviour of the eggs of Mugilidae has been variously described.
Sanzo (1936) observed that all fertile eggs of Mugil chelo sank soon after fertilization,
while Yashouv (1969) reported sinking towards the end of incubation for eggs of M.
cephalus. Kuo et al. (1973a) recorded that the majority of eggs of M. cephalus which
sank within the first twelve hours were undeveloped or unfertilized (absence of
perivitelline space). They noted that when eggs were prevented from settling by strong
aeration in small vessels survival was increased, and the incubation period reduced by
two hours at the same temperature. They concluded that water temperature and
turbulence had a decided effect on incubation time, and this was supported by Tung
(1973).
Tang (1964) noted that eggs of M. cephalus sank in standing water and so
incubated them in suspension by circulating water. Yashouv & Berner-Samsonov (1970)
described the development of M. capito eggs floating on the surface. Eggs of M.
cephalus lost their buoyancy after 20 h and sank, but hatched successfully. Sebastian &
Nair (1974) observed that eggs of M. macrolepis floated in shallow hatching trays, and
Liao (1974) reported that the fertile eggs of M. cephalus were buoyant and floated near
the surface. He maintained them in suspension during incubation by aeration as he
noted that some did sink later. The rearing practices of Nash et al. (1974) attempted to
maintain the fertilized eggs of M. cephalus in suspension by circulating water,
particularly when incubating at a density of 250 eggs/1.
Although incubation is apparently continued for eggs of M. cephalus which sink
below the surface, the artificial environment of a container for hatching obviously
introduces problems not normally encountered by eggs liberated in the sea. Density of
eggs during incubation is a key factor influencing hatching rates and overcrowding
produces problems of agglutination, bacterial contamination, oxygen depletion and
increased metabolite production. Suspension of the eggs by water movement counters
these problems, and few workers attempt to incubate fish eggs without the minimum of
circulation or water movement through aeration, particularly when operating at high
density.
Environmental conditions for incubation
Egg development and hatching time are both temperature dependent. Tang (1964)
reported that hatching of M. cephalus took place in 59-64 h at temperatures ranging from
20.0 to 24.5 °C and salinity from 24.39 to 35.29‰. Fertilization was low (32%) and the
rate of hatching was below 10%. Yashouv & Berner-Samsonov (1970) noted that under
laboratory conditions the eggs of M. cephalus and M. capito developed and hatched
within 36-44 h at 22-32 °C. Kuo et al. (1973a) stated that hatching of M. cephalus eggs
was evident 36-38 h after fertilization at 24 °C, and 48-50 h at 22 °C. Total length of the
newly hatched larvae was 2.65±0.23 mm. Salinity was 32‰.
Liao (1974) stated that hatching of M. cephalus eggs took place in 34-38 h at 2324.5 °C, and at 49-54 h in 22.5-23.7 °C, with salinities of 30.1-33.8‰. Tung (1973)
described the relationships between mean water temperature (∅) and duration of
incubation period (T) as Te 0.135 ∅ = 1262 in still water, and as Te 0.037∅ = 106 in running
water. Finally, Sebastian & Nair (1974) recorded the incubation lime of M. macrolepis as
23 h at 26-29 °C and 29-31‰ salinity.
Nash et al. (1974), Nash & Sylvester (unpublished data) and Nash & Kuo (1975)
report the survival of eggs of M. cephalus within broad ranges of temperature, salinity
and dissolved oxygen. Minimal mortalities of eggs occurred at 22 °C for normal sea
water (32‰), and an effective temperature range for incubation was 1 1-24 °C.
Most workers prefer a working temperature range of 18-24 °C for M. cephalus.
Above 25 °C incubation is inhibited although some eggs will hatch at 30 °C; the mortality
beyond 25 °C is usually above 90% and often total. Optimal salinities for incubation are
30-32‰ under ambient temperature conditions (19.5-20.5 °C), and significant decreases
in egg survival occur with eggs incubated in mean oxygen concentrations below 5.0
ppm.
Good temperature control during incubation is essential. Present work on the
propagation of M. cephalus is conducted within the most desirable temperature range
and mostly at the optimum level. Although individual daily temperature fluctuations may
be responsible for some egg mortality, it is believed that temperature per se is not
influencing the high mortalities experienced in the early stages of development. However
the working range of 18-24°C is suitable for rapid bacterial growth and therefore
indirectly a causative factor of environmental instability during incubation.
Kuo (unpublished data) recorded the change in osmolarity of the eggs prior to
spawning and that they were isotonic to sea water at the time of spawning This fact
together with the migratory behaviour of the adults at breeding time moving out into
oceanic water indicate that salinity level is most important for egg development, and
incubation should be conducted in full sea water.
Incubation facilities
Liao (1974) reported that fertilized eggs of Mugil cephalus prior to 1968 were incubated
and hatched in two types of hatching equipment. The first was a flowing water type. It
consisted of a tine mesh net hanging in the water and provided with a continuous slow
exchange of water. It was similar in design to that used for hatching eggs of Chinese
carp. The second was a static system of simple containers each with aerated sea water.
After hatching the larvae were transferred to other rearing tanks. The systems were later
modified to avoid loss of larvae during transfer. All development stages were then
completed in either plastic or large concrete tanks indoors with good environmental
control.
Kuo et al. (1973a) incubated eggs in well aerated static sea water (32‰) in 140 l
fibreglass tanks. Incubation temperatures were 22-24 °C. They worked on a series of
improvements and with Nash et al. (1974) developed a modified circular kreisel for
incubating eggs of M. cephalus. The advantages of the kreisel were that the eggs could
be pretreated with antibiotics to reduce bacterial growth and the density of eggs was
high for the size of the apparatus. Also separation of the emergent larvae from empty
shells and inviable eggs could be made during transfer of the larvae to the rearing
containers. This reduced potential fouling in the rearing tanks.
The kreisel has proved to be an effective rearing apparatus and can be
constructed in various dimensions. Aeration and circulation of the water are maintained
by an airlift pump located in the centre column. The water is drawn by the airlift pump
into the column through a large filter stone, aerated and passed back down the outside
of the pump and redirected into the container. A connection on one of the discharge
arms of the column directs a fraction of the water to waste, and that volume is replaced
by an incoming supply located above the column.
Nash et al. (1974) used ambient sea water (32‰) in the kreisel. Before use it
was treated by filtering, irradiating and treating with antibiotics. Both penicillin (10 lU/ml)
and streptomycin (0.01 mg/ml) were added daily and effectively reduced marine
bacterial growths. The eggs were suspended in sea water until after hatching and the
larvae safely transferred by siphon into larger prepared rearing containers.
Yashouv (1969) used specially designed incubators to prevent the washing out of
eggs with the changing sea water. Sebastian & Nair (1974) used shallow trays similar to
those used for the incubation of salmonid eggs.
Oppenheimer (1955) demonstrated bacterial growth on fish egg shells by
photomicrographs and found that the percentage hatch of a number of marine species
increased by controlling marine bacteria with a mixture of penicillin and streptomycin.
Shelbourne (1964) credited the successful culture of marine flatfish to the use of
antibiotics. Using controlled amounts of the two he demonstrated that the survival of
young flatfish was significantly increased from 40% to 60% at metamorphosis.
The antibiotic treatment in incubation tanks reduces bacterial activity around the
shell and prevents agglutination of the eggs. Physical damage to the egg shell, or the
covering of the shell with bacterial slime or mucus, breaks down the osmotic balance
between the eggs and the surrounding sea water. The osmotic regulation between the
two appears to be a key factor in successful propagation of marine and brackish water
species, and needs a great deal of further attention and research.
Although the effectiveness of antibiotics can be replaced by ultraviolet
sterilization and bacterial filters in the water system of a hatchery, the usefulness of
antibiotic treatments cannot be underestimated (Struhsaker et al. 1973). Nash et al.
(1974) utilized antibiotic washes and prolonged treatments during egg incubation.
Buoyant viable eggs at the gastrula stage were removed from the spawning tank,
washed under irradiated and filtered sea water, and then dipped for one minute in a sea
water bath containing potassium penicillin G (80 lU/ml) and streptomycin sulphate (0.05
mg/ml). They were then distributed into the kreisels at a density of about 250 eggs/1 and
incubation was continued for the remainder of the period. Low levels of antibiotic were
added daily and reduced all bacterial contamination.
Oppenheimer and Shelbourne theorized on the ways that bacterial activity
affected and damaged eggs (Costlow, 1969). Penicillin is effective against Gram-positive
organisms, and streptomycin against Gram-negative organisms. The combination
therefore sterilizes sea water if there are no resistant organisms present. Antibiotics
have also proved effective in the culture of shellfish (Walne, 1958). However they are
known to unbalance the mechanisms for calcium transfer in some species and could not
be used for the culture of Haliotis tuberculata (Nash, unpublished data). Although the
work of Nash et al. (1974) did not demonstrate fully the need for antibiotic treatment in
the culture of Mugil cephalus, the need for bacterial control is vital for successful
incubation of many marine and brackish water species.
Little mention is made in the literature on construction materials used for
incubation tanks. Shelbourne (1964) recommended the use of inert materials and the
incubators used in the first flatfish hatchery were made of black polyethylene. The colour
was important to provide a nonreflective surface against which the larvae could clearly
see living food particles. Other workers mentioned the use of fine mesh net containers of
terylene or nylon, but omitted to specify the materials of the larger container in which the
net bag was suspended. Both cement and fibreglass incubators have been used after
prolonged leaching of metallic ions or resins but plasticizers have proved damaging. A
great deal of information is lacking on the suitability of certain constructional materials.
Until good data are available most workers practise prolonged leaching of containers
either in a heated atmosphere or submerged under water.
Larvae and larval culture
Hubbs (1943) defined the terminology for the young stages of fishes and separated
prelarval, postlarval and juvenile stages on observed criteria. He considered that the
postlarval stage began immediately on absorption of the yolk sac, and lasted as long as
the structure and form were unlike that of the juvenile. The juvenile he considered to be
the young stage similar to the adults in all essentials.
For most teleosts the formation of the scales signifies the end of the postlarval
stage. The Mugilidae however develop scales in the early postlarval stages (at 8-10 mm
in length) and are soon well developed (at 12-14 mm in length). Hubbs criteria do not
therefore apply.
Roule (1917) divided the postlarval stage of Mugilidae into two successive
periods. The first had rudimentary scales as the diagnostic criterion followed by the
second stage with true scales. Anderson (1958) regarded the formation of the third spine
of the anal fin as signifying completion of the postlarval stage and classed individuals as
juveniles if the third anal ray had fused into a spine. Tung (1973) described five stages of
larval development and morphology.
Young mullet which first appear in small schools along the coasts and in the
estuaries are fully scaled. They measure 18-28 mm in length. Extrapolated growth data
for the species indicate that young of this size are between 30 and 45 days old. The
transition stage from postlarvae to juveniles used by Anderson (1958) does not occur
until the young are 35-45 mm in length or 45-60 days old. Thomson (1963) regarded the
transition complete at about 50 mm when the third anal spine formed from the anterior
ray and the adipose eyelid started to form.
For the purpose of this text the artificial propagation of the mullet must include
the culture of individuals to a stage of development when they can withstand relocation
from hatchery to nursery pond. Heavy losses will occur if the young fish are mishandled
or transferred too soon. This treatise considers young mullet up to 50 days old as the
responsibility of the hatchery. They are technically larvae until that time. Young fish will
be designated as juveniles when they are transferred from the hatchery to small ponds
and they should be at least 50 days old. This arbitrary classification closely fits the
morphological definition used by Anderson (1958). The use of the term 'fry' for young
fish is mostly avoided in the text. It is commonly used to describe all the resources of
postlarvae and juveniles collected along the coastlines and transferred to nursery ponds.
Morphology
Some of the first descriptions on the morphology of the larvae of Mugilidae were made
by Sanzo. He observed and illustrated the early stages of Mugil chelo and Mugil
cephalus (1936) and Mugil labeo (1937). He considered their prolarvae to be poorly
developed. They measured only 2.2-2.5 mm in length. The mouths were closed and
there were no traces of a branchial skeleton. Characteristic of the larvae were the
voluminous yolk sac and large oil globule often accompanied by smaller oil droplets.
The first complete morphologic descriptions of larvae of Mugilidae were made by
those workers involved in the induced spawning of the adults by hormone injection.
Mostly they described the development of M. cephalus. Among them were Tang (1964),
Yashouv (1969), Yashouv & Berner-Samsonov (1970), Liao et al. (1971), Kuo et al.
(1973a) and Tung (1973). Sebastian & Nair (1974) described the development of Mugil
macrolepis.
Newly hatched larvae of M. cephalus vary in length between 2.2 and 3.5 mm.
The oil globule (and any additional small droplets) is situated in the posterior part of the
yolk. Tung (1973) recorded 24 myotomes. He described the anterior half of the body
bent on the yolk sac. The larvae had five or six pairs of cupulae on the body side, from
eye to tail, and several pairs on the front of the head. Feeding began three to five days
after hatching. Yashouv & Berner-Samsonov (1970) gave full descriptions of the keys to
the eggs and larvae of five mullet species: M. cephalus, M. capita, M. saliens, M. chelo
and M. auratus.
Thomson (1963) reviewed work on M. cephalus and quoted in detail the
embryonic development described by Sanzo (1936) and Anderson (1958) A full and
accurate description of development and behaviour of M. cephalus was made by Liao
(1974), and is reprinted in Table 8.2.
Behaviour
Liao (1974) described the larvae of Mugil cephalus as having weak swimming activity
with the posture of belly up and head down, sometimes moving with a jerky motion up
and down. Kuo et al. (1973a) reported that newly hatched larvae were inactive and
usually remained upside down suspended in the water column in an inclined position
with the ventral side oriented towards the water surface. Occasionally each larva would
go into a jerky motion and right its position. It would then dart upward rapidly then sink
passively back to its resting position. They noted that sustained larval activity increased
after the second day.
The presence of the oil globule influences the activity of the larvae-during early
development. Kuo et al. (1973a) dealt at length with the vertical distribution of the larvae
and changes in specific gravity. They noted that larvae gained sustained swimming
powers between the tenth and twelfth days after hatching and documented vertical
distribution and measured specific gravity before that period. They observed that during
the first two days the larvae were passively suspended in the water column and tended
to become evenly distributed in depth a their specific gravity increased from 1.0263 g/ml
at 12 h to 1.0339 g/ml at 36 h after hatching.
They described a vertical migration of the larvae between the second and third
days. At the end of 60 h over 37% of the larvae came to rest on the bottom of the 80 cm
experimental column, with the remainder suspended in the lower 50 cm of the column.
After 72 h the pattern was reversed with over 85% of the larvae aggregated at the
surface. During this migratory period the larval specific gravity decreased from 1.0310
g/ml at 60 h to 1.0264 g/ml at 96 h by which time all the larvae were back at the surface.
The larvae remained at the surface until the sixth or seventh day.
Between the sixth and seventh day after hatching a second migration occurred. It
was accompanied by a similar increase in the specific gravity of the larvae on the
seventh day. All the larvae were on the bottom of the tank on the eighth day, with a
complete reversal on the ninth day. Conditions at the time were full sea water (32‰) and
ambient temperature (24 °C)
Table 8.2. Development of mullet larvae ami their behaviour (after Liao, 1974)
Days after Total length
hatching
(mm)
Development and behaviour
1
2.56-3.52 Newly hatched larvae had a large yolk and oil globule. The front part of
notochord being curved along the yolk sac and the curve degree related
to the duration of hatching. At low temperature this duration was long and
the curve more distinct. Weak swimming activity with the posture of the
belly up and head down, sometimes with jerky motion slightly up and
down. Pigmentation dependended on individual. Eye not coloured. Mouth
not developed. Digestive tube not well-developed.
2
2.64-3.28 Formation of organs was in progress. More pigmentation was found in
eye and body. The total length was shorter than before. Mouth was under
development. Bud of pectoral fin appeared. Nostrils were obvious.
3-4
3.11-3.53 Opening of mouth. Good development of upper and lower jaws. Irregular
peristalsis of stomach and intestines, able to take food. Yolk was
diminished. being 1 of original size. Oil globule was also reduced. It was
the first critical period, always accompanied by serious numbers of
deaths. Gill clefts appeared. Being attracted by and tending to
concentrate at 600-1400 lux area. Distributed at upper level during nighttime.
5-7
3.06-3 40 Digestive tube was well developed. Movement up and down individually
both during day and night. Feeding was easy to observe but only limited
in the day-time. Formation of abnormalities in the bladder and swelling of
hyoid could be inhibited by freshening of rearing water. Formation of
stomach, intestine, gall bladder, pancreas, gas bladder and continued
reduction of oil globule.
8
3.35-3.80 Complete disappearance of oil globule. Formation of gill filament. This is
the flexing point of the growth curve, with the growth starting to
accelerate.
10-13
3.45-5.10 Finfold moved backward. Gill filament well developed. Body surface
became dark in colour. Strong phototaxis. Formation of hypural bone. It
was the second critical period with very low survival rate.
14-15
3.85-5.70 Commencement of swimming in schools. Formation of urostyle. 7-9 ray
bases were found in each of anal fin and second dorsal fin. Gill lamellae
formed on gill filament.
16- 19
5.40-6.60 Seventeen soft rays in caudal fin. Black spots scattered on the whole
body. Shiny silver white complexion appeared from gill cover along
ventral part of anus. Schooling in upper levels, sometimes into middle
level.
20-21
6.00-7.65 Showing phototaxis during day-time while floating during night-time.
Appearance of brown colour sometimes and silver green at other times,
higher variety found in healthy larvae. Four soft rays on the first dorsal
fin.
22-24
8.25-10.9 Formation of complete 20 soft rays in caudal fin, 11 rays in anal fin, 6
rays in pelvic tin, 15 rays in pectoral fin. Fin membrane of dorsal fin and
pelvic fin almost entirely degenerated. Appearance of scales with 1-3
ridged circles. The size of largest scales reached 400 x 250 μm. Silverwhite complexion. In day-time. larvae swam in upper levels in schools
and against aeration and stream. At night they floated and scattered on
25-28
8.80-15.0
29--32
16.6-20.7
34-35
22.2-26.2
37-40
23.1-29.3
41
27.5-32.8
surface of water and liked to gather under the light.
All scales and fin rays were well formed. Silver-green complexion.
Appearance of teeth. Two nostrils separated.
Very sensitive. Gathering in smalt schools. In day-time, swam in middle
and lower levels, at night-time, continued to be floating but easily startled.
In day-time, larvae swam in large schools along the circle of rearing tank
in the middle and lower levels. In night-time, floating individually. Grassgreen in colour, sometimes silver-white on the dorsal part. Some
diseased fish were found with 'pop-eye' symptom.
Some changes in feeding behaviour, feeding at late afternoon. Sensitive
to light, and no longer gathering under light.
Strongly resistant to environment. Suitable for stocking.
Kuo et al. (1973a) concluded that the first sinking was probably related to the
rapid absorption of the yolk sac and the resulting change in specific gravity. Planktonic
larvae are normally able to distribute themselves through the surface waters. This ability
may be more pronounced in Mugilidae because of the continuous references to the
spawning of the adults over deep water (see pp. 270-5) and the rarity of eggs and larvae
taken in plankton tows.
The second descent could not be fully explained. Although the larvae were not
capable of sustained swimming at the time, they were capable of swimming to the
surface of the water column. Kuo et al. (1973a) could not account for the sudden and
transient increase in specific gravity of the larvae on the seventh day. Morphological
observations of histologic sections of the larvae revealed that the pneumatic duct of the
air bladder was occluded between the sixth and seventh days, but the relevance of this
was not understood. The migration was known not to be a phototropic response.
During the mass propagation of the larvae Kuo et al. (1973a) experienced heavy
mortality at the critical stages associated with the two migratory periods. They attributed
the mortality to mechanical and physical damage during prolonged contact with the
bottom of the container as the larvae had no control over their ability to escape. The
mortality was reduced slightly by using deeper containers (1.5 m) for rearing.
Nash et al. (1974) used a rearing kreisel and increased survival significantly
during the first migration. The kreisel provided mechanical circulation but the larvae were
protected from the damaging effects of strong aeration by a simple central device.
Summarizing the migratory behaviour they believed that the larvae were responding first
to changes in utilization of the yolk and sank to the bottom. After ascending the larvae
had improved musculature control and lost the indiscriminate floating activity much
earlier than previously stated.
The second vertical migration was associated again by Nash et al. (1974) with
the changes in specific gravity of the larvae and suggested that two factors were
concerned. The first was associated with the physiological and morphological changes,
the second with nutrition. They observed that there were distinct differences between
feeding and nonfeeding larvae as early as the seventh day after hatching. Established
larvae were longer and more active, and were intensely pigmented. Unestablished or
nonfeeding larvae remained in the surface water layers and used the increased surface
tension along the sides of the container to support themselves. Development of the
pigment was slow and little or no growth was evident. Such larvae died between day 7
and day 10 depending on the water temperature. Coincidental with the migratory
movement of the larvae to the bottom, many undeveloped individuals sank because they
were unable to sustain themselves further and were moribund. Hence the earlier
association of heavy mortality with the migratory period. Developed larvae also had to
undergo the changes associated with the migration which must be critical to further
development. As with other larval forms undergoing metamorphosis the mullet larvae
became inactive for a period and sank.
All workers now believe that those larvae which survive the second migration are
capable of full development, providing that the conditions and food are suitable and if
they are not mishandled. Established larvae after the second migration soon develop
scales and then school together.
Nutrition
The dearth of larval Mugilidae in plankton tows is responsible for the lack of information
on their natural foods during this critical stage of development. This scarcity of
knowledge during the first formative fifty days of life is to some extent compensated for
by the wealth of data on the food and feeding habits of juveniles and adults of Mugilidae
from regions throughout the world, e.g., Hiatt (1944) Jacob & Krishnamurthi
(1948),Thomson (1954), Sarojini (1957), Hickling (1970) and Zismann, Berdugo & Kimor
(1974). However, this is not in the scope of this chapter.
The data on acceptable foods for the larvae of Mugilidae have been produced by
workers developing culture techniques, usually following induced spawning practices.
The variety of larval foods which have been tried and evaluated by fish culturists working
with many marine and brackish water species has been reviewed by May (1970).
Aspects of food and nutrition of marine fish larvae important to the best culture practices
have been developed by Houde (1972).
Following the format of May (1970), Table 8.3 lists the food organisms and
prepared foods which have been used by culturists in their search for an adequate food
for the larvae of the Mugilidae. The sources are predominantly the publications of
workers in Taiwan, Israel, Hawaii and India and in most cases were tried on the larvae of
Mugil cephalus.
Emergent larvae of the grey mullet are believed to be entirely carnivorous during
early development, becoming omnivorous and capable of digesting plant material some
time before metamorphosis. The most successful larval rearing results of Liao et al.
(1971), Kuo et al. (1973a), Tung (1973), Nash et al. (1974) and Sebastian & Nair (1974)
indicated the use of a mixed dietary regime during the first ten days of life.
Many workers include wild or natural zooplankton in their regimes. Shehadeh &
Kuo (unpublished data) had some success with the nauplii of Artemia salina fed alone
on the seventh day after hatching, but the results were later improved with a
phytoplankton supplement (Kuo et al., 1973a). Sebastian & Nair (1974) noted that Mugil
macrolepis fed exclusively on copepods but grew best on copepods prepared in
association with an algal bloom, particularly Chlorella species.
Table 8.3. Experimental foods for larvae of grey mullet species, tried at one time
or another
1.
2.
3.
4.
Wild plankton
Protista
Duneliella sp.
Prorocentrum mirans
Chlarella sp.
Oxyrrhis species
Gymnodinium splendens
Cuscinodiscus species
Isochrysis galbana
Chaetoceros species
Monochrysis lutherii
Biddulphia mobiliensis
Skeletonema costatum
Ditylum brightwelli
Thalassiosira species
and unidentified phytoplankton. diatoms
Nitzschia species
and green water
Platymonus subcordiformis
Cryptomonas maculata
Metazoa - planktonic forms
Brachionus plicatilis
Arbacia species
Artemia salina
Crassostrea gigas
and unidentified Copepods
Prepared formulations, including at one time or another
Cod liver oil
Artemia salina
Powdered oil-cake
Copepods
Bean cream
Oyster flesh
Fish ovaries
Fish meal
Egg albumin
Urea
Boiled egg yolk
Rice bran and flour
Liver juice and enzymes
Milk powder
Amino acids
Powdered oats
Marine vitamins
and commercially available tropical fish
Brewer's yeast
feeds
Freeze-dried phytoplankton
Freeze-dried zooplankton
Many culturists rearing marine and brackish water species of finfish and shellfish
believe that the presence of phytoplankters in the rearing containers is beneficial to the
technique, but not always of direct value as food. Although some phytoplankters are
found in the gut of prolarvae it is not thought generally that they are nutritionally
sufficient. The indirect benefits of phytoplankters are probably the stabilization of the
rearing environment through the removal of metabolites, or the supplementation of
necessary marine vitamins or amino acids in solution, or for maintaining the nutritional
level of the zooplankters before they themselves are consumed.
Several artifical diets compounded from both natural and synthesized materials
have been fed to the larvae of mullet with limited success. Most have the disadvantage
on artificial diets in association with natural organisms. Against the poor larval survival
data, which may be the result of other factors, the true nutritional value of many artificial
diets cannot yet be estimated satisfactorily.
Nash & Kuo (1975) hypothesized that the larvae of the grey mullet were able to
utilize at least one or several of the live or inert dietary organisms listed in Table 8.3. It
was their belief that it was the preparation, feeding procedures and practices which,
among other things, were at fault and not the types of organisms tested. They stated
several instances for the human influence to be an unintentional cause of larval mortality
during larval feeding. For example, separation of the food organism from its own rearing
medium was not always adequately performed, and the separation of the nauplii of
Artemia salina from the cysts was often inefficient.
The selection of the food organism by the larva is made, in all probability, on the
simple criteria of movement and size in the first instance. The ability of larvae to feed is
regulated by feeding behaviour and vision. Blaxter (1969a) described the visual
thresholds and spectral sensitivity of a number of marine species. As with many marine
and brackish water species the eyes of the larvae of Mugilidae are large at hatching and
become rapidly pigmented within three days. The eyes are only capable of coarse
movement perception and, as with other fish species, are poorly equipped visually with a
single type of visual cell. They have little ability to adapt to dark or light situations during
the first hours after hatching. Most culturists follow the early techniques of Shelbourne
(1964) and try to improve conditions for feeding by providing nonreflective dark surfaces
for the rearing containers. The food organisms are clearly silhouetted as they move
around.
Hoade (1972) believed that food organisms within the size range 50-100 μm
were preferred by fish larvae with relatively large mouths. The acceptable sizes of food
increased rapidly as the larvae grew. The recent successes of a number of culturists
using the rotifer Brachionus plicatilis (Theilacker & McMaster, 1971), in association with
a number of phytoplankters, infers that the size of about 100 μm is adequate for the first
two days of feeding the larvae of the Mugilidae.
The ratio of food or organismic density to the larval density is another key factor
to successful larval culture irrespective of species. The optimum food density must be
maintained continuously through to the end of the larval period.
A superabundance of food can be as harmful as too little. A larva must not be
intimidated by large or quick-moving organisms or totally dominated by a number of
them in one location; for example organisms collect in a corner where the light intensity
is often increased by the high light reflection of an interface. Conversely the density of
larvae can be too high. In addition to the problems of inhibitors produced by the larvae
when overcrowded (Blaxter, 1969b), the physical contact, the increased competition for
space and food and production of metabolites all lower the survival rate. Kuo
(unpublished data) showed a higher survival of larvae of Mugil cephalus at 12/1 than
either 8 or 16/1. Shelbourne (1964) operated at higher densities for Pleuronectes
platessa; a similar survival of about 70% was obtained from two populations of
established feeding larvae at 28 and 56/1. During development to metamorphosis the
survival decreased to 30% and the density to 12 and 24 larvae/l respectively. May,
Popper & McVey (unpublished data) successfully reared the larvae of Siganus
canaliculatus at a density of 5/1. The data in Liao (1974) indicated effective rearing at a
density of less than 10 larvae/l. Each individual larval form must be provided with the
opportunity to observe and attack live food particles. Many failures occur, particularly
during the first crucial days of the learning process, and a larva without success cannot
survive for long.
Riley (1966) and Rosenthal & Hempel (1970) concluded that a higher food
concentration was necessary at the time larvae initiated feeding than subsequently,
probably because the younger stages were less capable of capturing food. Houde
(1972) recommended a food level using wild zooplankton (copepod nauplii and
copepodites) of 3.0/ml for the first two days of feeding larvae, but a level of only 1.5/ml
on subsequent days. If rotifers were used he suggested a higher concentration. If only
nauplii of Artemia salina were fed then he recommended a lower concentration.
Nash & Kuo (1975) specified an organismic density of 20-30/ml during the first
feeding stages of Mugil cephalus which included all organisms. Liao et al. (1971)
described the use of fertilized oyster eggs and cultured diatoms on the third day of
development. Liao (1974) stated that the density of oyster eggs or trochophore larvae
was maintained as high as 400-500 organisms/ml. Yeast and albumin were then added
as supplements on day 4 and rotifers and copepods on day 6.
Kuo (unpublished data) showed that feeding larvae of M. cephalus first on days 4
or 5 was better in terms of survival and management than that on either days 3 or 6.
Furthermore, copepods smaller than 150 μm were not utilized until day 5. He also
performed four series of experiments feeding emergent larvae with Isochrysis,
Brachionus, Chlorella or natural zooplankton. Observations of stomach contents during
development between days 5-11 were made. Isochrysis was taken first of all food
organisms tested and ingested in quantity on day 5 after hatching. The food preference
of mullet larvae for natural zooplankton or Isochrysis as an initial food was further
examined. Again the food organisms were given singly and in combination and the gut
contents examined daily. No food preference was indicated except Isochrysis was once
more consumed readily on day 5.
The logistics of aquaculture for the hatchery operation for marine and brackish
water fish are considerable. If certain species of fish require individual organisms over a
long period of their development, it is possible that the larval food production system
alone will be greater than that of the fish larvae themselves. Shelbourne (in Costlow,
1969) quoted a daily requirement of 200 million nauplii for a flatfish hatchery producing
0.5 million juveniles. That is why the dehydrated cysts of Artemia salina are such an
advantage at present as they can be conveniently stored and prepared with a minimum
of delay and acclimation (Nash, 1973). It also explains the strong interest in artificial
foods.
The present methods of larval culture which are proving most successful are
those using a mixed dietary regime, often by the creation and stabilization of an
ecological system. The 'green water' technique has been used successfully by Fujimura
& Okamoto (1972) for the culture of Macrobrachium rosenbergii, and by several
Japanese in the culture of penaeid prawns.
The use of the mixed dietry regime has several advantages. It requires culture of
several species in one container before the relase of the fish larvae. Following the
preparation of the system with cured or conditioned sea water the environment becomes
stablized. There are few rapid and diverse environmental changes which can upset the
delicate biochemical balance of the larvae. The mixed regime is also economic in
decreasing the numbers of individual organisms which have to be produced on a daily
basis. The wide choice of organisms probably provides a better qualitative as well as
quantitative diet for the larvae and also permits individual larvae to develop at their own
rate by feeding on organisms relative to their size.
Pelagic copepods according to House (1972) were probably ideal food for marine
fish larvae. Liao (1974), Nash et al (1974), Kuo et al. (1973a) and Tung (1973) all used
natural zooplankton in their respective feeding regimes. It was the copepods which
proved to be the most significant and beneficial organisms for the diet of the larvae of
Mugil cephalus. The Japanese culturists regard copepods as the best larval fish food
(Harada, 1970) and consequently there have been many attempts to rear them
intensively. In many cases large natural populations can be found in the filamentous
green algae which grow in the enclosures retaining the broodstock or maturing juveniles.
Environmental conditions for rearing
Salinity is probably the most unregulated and uncontrolled major parameter which
influences the incubation and larval rearing of marine species. The majority of workers
conclude that natural high saline waters (32-35‰ are optimum, The eggs of most marine
and brackish water species are liberated into oceanic waters and, with the emergent
larvae, are adapted to develop at high salt concentrations. Holliday (1969) concluded
that survival of embryos and larvae of many species could be increased at low salinities
(10-16‰ because those levels were iso-osmotic with body fluids. Houde (1972) found
that many species had high survival rates over a wide range of salinities. He did not
consider salinity as critical as some other rearing tank conditions which affected growth
and survival.
In Israel, Taiwan and Hawaii, where the majority of work has been accomplished
on the rearing of Mugil cephalus, offshore salinities and experimental conditions are all
very similar, namely 32-35‰ with up to 39.5‰ for the eastern Mediterranean. Sebastian
& Nair (1974) operated at slightly less (29-31 ‰) for the culture of M. macroepis.
However, the effect of salinity on larval survival and development is possibly more
significant than that for incubation of the eggs.
Liao et al. (1971) reduced the salinity from 32 to 26‰ during larval development
in three stages commencing on the sixth day after hatching. They concluded that there
was an advantage rearing the larvae of M. cephalus in diluted or sweetened sea water.
Nash and Sylvester (unpublished data) provided tolerance levels of larvae of M.
cephalus to varying salinities. They showed that the larvae could only withstand
prolonged exposures to salinities of 25-34‰ at 20°C during the first week of
development, with an optimum at 26-28‰ for 96 h exposure.
The operational procedures for the culture of M. cephalus as outlined by Nash et
al. (1974) in Hawaii did not include techniques for reducing the salinity of the water
during the first fourteen days. They used full saline conditions until completion of the
second migration and then made dilutions. Better results were reported by Liao (1974) in
Taiwan with the dilution technique.
Nash & Kuo (1975) theorized on the value of reducing salinity during early
development and hypothesized that there was a link between the need to change salinity
and the second vertical migration of the larvae (see pp. 287-90). They believed that the
unexplained rise in specific gravity at the start of the second migration was unnatural
and a result of osmotic imbalance. The larvae had not sufficient fresh water internally to
maintain the balance and consequently sank. The larvae must therefore be cultured in
sea water which is changed to suit the osmotic regulation. Such fine control was an
external compensating reaction against the change in specific gravity. They also
contended that the fresh water consumption of the larvae needed increasing and both
cultured and artificial food preparations required greater consideration for fresh water
content.
Larval development is temperature dependent. Shelbourne (1964) demonstrated
the need for optimum temperature control for the culture of marine flatfish. He also noted
differences between the survival of larvae in natural conditions and those in the intensive
hatchery environment where bacterial activity was potentially more dangerous. The
reasoning of Shelbourne is particularly relevant to the culture of fish and shellfish in the
tropical and subtropical latitudes. There the ambient temperatures are highly conductive
to bacterial growth, and the optimum rates for yolk utilization by the larvae are probably
narrowly defined and close to a critical level.
Strict temperature control for the incubation of the eggs of the Mugilidae is
important (sec pp. 282-3). Emergent and developing larvae up to metamorphosis
tolerate an ever widening temperature range and their growth rate responds accordingly.
Liao (1974) reported the successful culture of the larvae of Mugil cephalus over a
number of preceding years within the ambient temperature range of 19-24 °C. Nash and
Sylvester (unpublished data) recorded minimum mortality of the larvae of M. cephalus
between 18.9 and 25.3 °C, although some larvae survived temperatures as low as 15.9
°C and as high as 29.1 °C. Sebastian & Nair (1974) operated within a higher range of
26-29 °C for the culture of Mugil macrolepis.
It is believed by Nash & Kuo (1975) that, of the two development stages of egg
incubation and larval growth, the former was more critical and required careful
temperature regulation. Nash & Shelbourne (1967), working in the thermal discharges of
coastal electrical generating plants, exposed the eggs and larvae of marine flatfish at
various stages of development to the elevated temperatures. Emergent and developing
larvae were able to withstand substantial thermal shocks and grew rapidly at the higher
temperatures. The early start to growth produced significant savings in time taken to
reach market size. However, there was no benefit in attempting to use elevated
temperatures to increase the rate of egg development as survival was in fact decreased.
A great deal of data on survival and temperature is available for juveniles of the
Mugilidae, but is beyond the scope of this chapter which deals with the production of
larvae up to 50 days.
Little information exits on the levels of dissolved oxygen suitable for the rearing of
the larvae of the Mugilidae. Although the levels of dissolved oxygen are measured
regularly as part of many culture operations, the data are often excluded from reports.
Nash and Sylvester (unpublished data) determined that the survival of the larvae of
Mugil cephalus was significantly changed for mean oxygen concentrations below 5.4
ppm.
The size of the culture system does not necessarily influence the success of a
mass propagation effort. Many workers operating in carefully monitored small units, and
with high density feeding but low larval density, have produced exceptional survival
figures. However that is not aquaculture. In terms of mass propagation the larger units
are more appropriate for rearing the numbers of larvae which are necessary for a culture
practice to become economic.
The successful culture system of Fujinaga (1963) with Penaeus japonicus
encouraged both Liao et al. (1971) and Nash et al. (1974) to use larger containers for
the culture of M. cephalus. Survival of the larvae in them was definitely increased but the
reasons were obscure. At present the usefulness of the larger container may be in the
lowering of larval density and increasing spatial freedom. It would also decrease the
influence of any specific inhibitors released by the larvae, and prevent a size hierarchy.
However, they stocked the containers with eggs or larvae at 50-250/1 initially, with a final
density of between 5 and 50/l on day 21.
The disadvantage of the larger container is the great demand on available larval
food, particularly as food density is a key factor for survival. The logistics to supply the
larval food on a single species daily supply basis would be tremendous for a farm of any
size. Shelbourne (in Costlow, 1969) operated an intensive Artemia salina nauplii system
capable of producing over 200 million nauplii per day. However in the context of a mixed
feeding regime (see pp. 293-4), populations of differing organisms can make up the
organismic content to the required density in the simplest way.
The advantage of the large container as theorized by Nash & Kuo (1975) is the
stabilizing of the rearing environment. Although good tank hygiene is necessary and
water has to be replenished and salinity reduced, the effects of the exchanges or the
additions of food are buffered by the size of the system. The larvae are therefore
protected from sudden shocks or exposure (albeit for a short period) to adverse
conditions.
Little data are available on the suitability of materials for containers for rearing
the larvae. A study of the effects of materials on several small marine organisms was
made by Bernhard & Zattera (1970). Plastic, polyethylene, fibreglass, concrete, vinyl and
wood have all been used at some time for Mugilidae with little comment on their value or
suitability. Most workers leach potentially toxic chemicals and plasticizers from moulded
or fibreglass units.
The colour of the rearing units can be important. Nonreflective black polyethylene
tanks to prevent areas of high light intensity have been widely adopted. An even light
intensity over the tanks prevents localized gathering of the larval food and the larvae.
Exposure of larvae to direct sunlight has to be avoided and all rearing operations are
preferably conducted indoors. Liao (1974) noted that the larvae were sensitive to light.
Four-day old larvae exhibited phototaxis and six-day old larvae migrated up and down
according to the time of day, but fed only in the day. Larvae avoided strong illumination
but were attracted by dim light intensity of about 600-1400 lux.
Post larval development
Between the present critical stage of early development (day 12-14) and the juvenile
stage there appear to be few problems. The larvae which have survived beyond day 14
are usually hardy, feed well and grow rapidly. By the end of the third week the scales
begin to appear and the larvae school together.
Growth is rapid. The larvae feed voraciously on nauplii of Artemia salina,
phytoplankters, diatoms, copepods and artificial dry preparations.
Water flow through the rearing tanks can be increased or replaced by strong
aeration. The most damaging effect is handling. Many larvae undergo a handling trauma
and become inactive and die after violent quivering. Handling is not advised until the
larvae are juveniles and ready for transfer.
Culture technique
From the results obtained by Kuo et al. (1973a), Tung (1973), Nash et al. (1974),
together with a decade of information from Taiwan summarized by Liao (1974), the
following culture technique combines the best practices for . the artificial propagation of
the grey mullet, Mugil cephalus. It can probably be applied to other Mugilidae with minor
modifications.
Although the survival rate of established larvae has been reported as high as
19.5% in Taiwan and 25.5% at 14 days in small tanks in Hawaii, the technique holds no
guarantees. However a considerable amount of good information has been assembled,
far more in fact than was at the disposal of the White Fish Authority of the United
Kingdom before it successfully developed the fust marine fish hatchery for flatfish in
1963 (Shelbourne & Nash, 1966). There are certainly sufficient data for construction of a
pilot scale hatchery to improve the methods and demonstrate the techniques, and also
to learn of the new problems produced by the increased scale of operation.
Broodstock
Four-year old broodstock should be used, maintained healthily in captivity in sea water
of 32-35‰ salinity and at 20-22 °C. The resources of broodstock can be either migratory
fish about to spawn or a resident pond population. The latter is preferable but the stock
should be replenished each year with additional individuals. The population should be
sexed and the two maintained separately.
Egg samples should be taken regularly from the females and measured to
determine development. The eggs must be above the critical stage (preferably 650 μm in
diameter) before spawning is induced.
If purified salmon gonadotropin is used a total dose of between 12 and 21 μg/g
body weight is necessary per female and is applied in two injections. The time interval
between injections is 24-48 h depending on observed egg development after the priming
dose. Alternatively, fish can be induced to spawn by injecting a total dose of 2.5-6
pituitary glands of mullet, 10-60 RU of Synahorin, and 0-300 mg vitamin E. The time
interval between two injections is 24 h. The females usually spawn 12 h after the second
injection.
Spawning in (he natural season
Spawning is prefaced by hydration of the oocytes characterised by sudden enlargement
of the abdomen and deposition of calcium. Two hours before spawning the males can be
released with the females in a ratio of 3: 1. The females can be spawned either as
individuals in isolated aquaria or within a population in a large tank. The spawning fish
should be maintained in seawater (32-35‰) and at 20-22 °C. In small aquaria the
seawater should be flowing rapidly through the system and the water strongly aerated. A
few seconds before spawning the seawater is shut off but the aeration continued In the
large tanks an exchange of sea water is maintained but the outlet is protected by a
suitable fine mesh screen.
Preferably all spawning should be performed indoors with environmental controls
for temperature and subdued light, and with a minimum of disturbance. Natural
spawning is preferred but fertilization can be completed if necessary by either the
standard dry or wet methods.
About one million eggs per female are released. Fertilization can be estimated
one hour after spawning by microscopic examination of a sample of eggs. The eggs are
extremely buoyant and can be removed from the surface of the spawning tank with a
soft fine mesh net and transferred to the incubators. If individual females are spawned in
small aquaria then the eggs should be dispersed among other tanks and aerated.
Spawning out of season
Spawning out of the natural season can be induced if environmental control facilities are
available. The fish should be conditioned for a period of about 120 days before the
desired spawning time. A combination of a retarded photoperiod (6 L/18 D) and constant
temperature of 21 °C is effective for the development of oocytes. Both males and
females should be exposed to the conditions and can be kept together.
Samples of eggs should be taken from the females regularly to determine the
state of oocyte development. If the fish are in the refractory stage at the start of
conditioning, the first signs of development (stage II) should be visible after about 60
days. Oocytes in the tertiary yolk globule stage (stage III) can be anticipated after about
120 days, and will be ready (above 650 μm) for hormone injection any time thereafter.
The methods of inducement are the same as described in the previous section, although
an additional injection may be necessary.
Egg incubation
Egg incubation is performed as a separate hatchery process in specially designed
containers to maintain strict control over the environmental parameters. This avoids any
overloading of the rearing kreisels, as they have to be prepared with larval food.
One hour after spawning and fertilization the aeration in the fish spawning tanks
is stopped. The fertile buoyant eggs rise to the surface of the tank and can be removed
in small numbers with a soft fine-mesh hand net. The eggs in the net are washed gently
in running irradiated and filtered sea water and dipped for one minute in a sea water
bath containing the antibiotics potassium penicillin G (80 IU/ml) and streptomycin
sulphate (0.05 mg/ml). The eggs are then distributed throughout several incubators at a
density of no more than 400 eggs/1. The incubators are circular in design and fabricated
with an inverted conical base to prevent eggs settling on the bottom during incubation.
The aerator is located at the very base of the incubator in the cone to provide maximum
circulation.
The incubators are filled prior to egg transfer with sea water of 32-35‰ salinity
and maintained at 20-22 °C. The water in the incubators is also sterilized and filtered
during filling, and thereafter treated with antibiotics at a dose rate of 10 IU/ml of penicillin
and 0.01 mg/ml of streptomycin per day.
Under such conditions incubation will take between 50 and 60 h to complete.
Incubation should always be performed indoors under subdued indirect lighting (1400
lux) and maintained at constant temperature.
Larval rearing
After 60 hours incubation is complete. The emergent larvae are then ready to be
transferred slowly by siphon to the rearing kreisels. Before siphoning, the circulation in
the incubators is stopped when the viable larvae soon occupy the upper levels of water.
The empty egg cases and unhatched eggs sink, and care should be taken to avoid
transferring them with the larvae.
The rearing kreisels are prepared several days in advance. Conditioned or aged
sea water is used to fill each one. Alternatively the sea water is sterilized and filtered
during the filling operation. The sea water must be 32-35‰ salinity and temperature
maintained at 20-22 °C before receiving the larvae. Before the larvae are transferred into
the kreisels, each kreisel is inoculated with cultures of either Dunaliella or Chlorella, or
other phytoplanktonic species capable of supporting the rotifer, Brachionus plicatilis.
Chlorella species are preferred.
The organismic content of the kreisels should be monitored daily before and after
loading with larvae. The objective is to achieve a density of 104 -105 particles/ml of which
10/ml should be rotifers of suitable size. The preferred size of established rotifers is 100250 μm. Given these organismic densities in the first three days, the food ecosystem will
maintain itself and its numbers to support the increasing demands of the developing
larvae over the first twenty-one day period. Thereafter, beginning on day 14, the diet can
be supplemented with the day-old nauplii of Artemia salina, continuing until day 40.
Older nauplii and artifical food can then be used. The density of the larvae in the rearing
kreisels at transfer should be no more than 6/1, with an anticipated larval density at day
21 of about 0.33/1.
The rearing kreisels should be as large as possible, but of dimensions in keeping
with the hatchery building, environmental controls, available resources of water and air,
and particularly the resources of larval food. Concrete, fibreglass, polyethylene and butyl
lined containers are all acceptable materials for the kreisels, following prolonged
leaching in water or a heated atmosphere. The sides should be dark in colour and it is
useful to paint the internal base of the tanks white. Depth is not important and 1 m is an
average dimension so that tanks can be used for other purposes after the rearing
season. If the tanks are fabricated specially for the purpose of rearing, the design should
include protected inlets and outlets in addition to features which facilitate capture of the
juveniles after 50 days.
Each tank should be fitted with an overhead diffused light giving an intensity of
no more than 1400 lux at the surface. Regular illumination with separate controls should
be available.
Temperature controls should be available to maintain the air and water
temperature al 20-22 °C although there are indications of improved growth at 24 °C from
day 1. The initial salinity of the sea water in the tanks should be 32-35‰. The water
provided for the tanks should preferably be from a reservoir where it is passed
continuously through filters and sterilized by ultraviolet lamps.
On day 4 after hatching, the water in the rearing tanks should be diluted with
fresh water at a rate which decreases the salinity by 0.5‰ per day to produce a salinity
of 30‰ by day 7. Thereafter it should be decreased regularly each day to 20‰ by day
30 and then maintained for the remaining 20 days of operation.
Daily records should be kept of temperature, salinity, dissolved oxygen and pH
levels. Daily determinations of nitrite, nitrate, ammonia, sulphide and phosphate are also
useful. Until the exchange of water through the rearing kreisels becomes substantial,
these metabolites accumulate in the first 21 days. Although the tolerance limits to the
individual metabolites are not yet known, as yet unpublished data indicate that the
following levels can be tolerated and are presently considered acceptable but not
desirable. Nitrite up to 3.00 μg, nitrate up to 90.00 μg, ammonia up to 30.00 μg,
phosphate up to 9.00 /ug and hydrogen sulphide up to 5.00 μg at day 1. Preferably the
levels of metabolites should be as low as possible and not fluctuate radically. Dissolved
oxygen levels in the kreisels should preferably be above 7.0 ppm, and pH between 7.9
and 8.3.
The rearing kreisels should be cleaned daily with a small siphon and dead larvae
and uneaten food removed. With large tanks cleaning is not always easy as parts of the
tank may be inaccessible. Circular tanks have the advantage of self cleaning either by
moving the debris to the centre where it can be extracted by siphon, or by exhausting
through the central standpipe. The latter is most effective when the rate of water
exchange is high and the flow rate can only be increased when the larvae are
established and strong (over 30 days old).
Between days 30 and 50 the growth of the larvae is rapid and they readily accept
moistened artificial food, older nauplii of Artemia salina and larger copepods.
Mullet younger than 40 days old should not be moved or handled: Almost all
react traumatically to handling and die. In consequence the hatching and rearing activity
should be considered as a 50 day operation, although the young fry can be handled
safely after 40 days and demonstrate schooling behaviour.
Speculation for the future
The Mugilidae probably have the brightest future of all the marine and brackish water
finfish in the developing technology of aquaculture. The majority are desirable fish with
good flesh texture and taste, particularly when captured or taken from water of high
salinity. They are distributed widely and have a capacity for tolerating extreme conditions
of temperature, salinity and dissolved oxygen. They are naturally hardy animals which
thrive on good husbandry but are also capable of withstanding poor farming practices.
The many species of Mugilidae give them genetic potential unparalleled by few
other aquatic species. It will be the manipulation of the genes and the selection of strains
and breeding lines which will make them the aquatic equivalent of the first fatstock land
animal.
Sufficient knowledge on the artificial propagation of Mugil cephalus has been
produced to justify an investment in a pilot scale hatchery operation. The purpose of the
hatchery would be to improve the existing techniques by operating at the increased
scale, demonstrate the system and produce a large number of juveniles annually to use
for farming experiments in management and production.
The logistics of such a hatchery need specifying so that the involvement is
understood. Indoor tank facilities covering 3000 m2 of floor space are estimated for a
pilot-scale hatchery designed for the instantaneous production of one million 50 day old
juveniles. Estimates are based on technical data from the previous section with
anticipated overall survival of 5% of the original number of eggs after 50 days. For
example, fifteen females and forty males will be the minimum requirement for the
broodstock. At least twice that number should be held in reserve in indoor tanks or small
ponds, each with a capacity of 1 m3 per fish. The fifteen females will provide a minimum
of 18 million eggs of which 5% are expected to survive development to the juvenile
stage. Spawning can be achieved in several small aquaria located in a breeding room. It
should be phased over a 16 day period with three females induced every fourth day.
This increases efficiency through the hatchery and reduces the demand on space and
facilities and on the larval food resources.
The eggs from each female will be transferred after twelve hours into the circular
and conical incubators, each 1.5 m deep and 1.25 m3 capacity. After hatching all the
tanks will be sterilized and cleaned in preparation for the next batch of eggs.
Three hundred circular larval rearing tanks will be required, 1 m deep and 10 m3
each in capacity. Previously the tanks will have been prepared and conditioned in
groups with each group ready for larval reception every fourth day.
The food production unit will be considerable. Although continuous culture
systems are being developed for the production of larval foods, batch cultures at present
are more reliable. For the mixed phytoplankton culture system required to inoculate the
larval rearing tanks for initial cell density of 104-105 cells/ml at stocking, a total of nine
tanks of 10 m3 capacity will be required for each of the groups of fish larvae being
processed. The culture would continue to enable this density to be maintained if
additions were required. A total of four tanks of the same capacity will be required to
supply batch cultures of Brachionus plicatilis at an initial stocking rate of 10 /ml and then
to supplement daily with the same number if required. It is estimated that sufficient
supply of small copepods (2/ml) could also be obtained from four 5 m3 capacity outdoor
ponds, suitably inoculated and with a good growth of micro-algae.
In addition to the culture units it will be necessary to have an Artemia salina
nauplius incubator capable of a daily output of 200 million nauplii per day.
The overall water requirement for the system excluding the larval food unit is
nearly 3200 m3. A storage reservoir of 50 m3 should be available together with a service
reservoir of 20 m3 in which the water is continuously circulated and treated. Together
with service laboratories and accommodation, the entire facility could be housed in a
single story building occupying 4000 m2 of floor space. An estimate team of twelve staff
and technical aides could operate the hatchery.
As demonstrated by the White Fish Authority at their marine flatfish hatchery in
Britain, the pilot operation is necessary to define problems not apparent in the enlarged
laboratory practices, and to learn the economies of scale. After twelve years of
development with hatchery production, a basis for the commercial production of flatfish
is now very much refined. Larval rearing density has been increased considerably
through management experience and consequently has made a significant saving in
capital construction requirement.
For the mullet hatchery, tripling the final rearing density to 1 larval by increasing
survival from 5 to 15%, the same facilities could be used to produce 3 million juveniles
over a period of less than 2½ months; alternatively the facilities and capital cost could be
reduced by two-thirds for the original production of one million larvae. With
environmental manipulation facilities to provide spawning fish on a year round basis, the
same facilities could produce 15 million juveniles per year. Tang (1974) estimated that
the aquaculture fishery of 2000 metric tons of grey mullets in Taiwan is based on the
collection of 10 million juveniles annually.
In addition to the advantages of genetics for increased growth and production in
ponds, genetic engineering and cross-breeding within the Mugilidae may result in the
production of larvae with hybrid vigor sufficient to increase survival and for rearing at
increased density. The benefits of genetic engineering were described by Purdom
(1972). He said that gynogenesis promised to be a rapid way of producing inbred lines,
and the production of artificial triploids already showed greater growth rates than the
diploids. Triploids also had the advantage of being sterile, which has always been a
significant factor in fatstock production.
Liao et al. (1972) reported the problem of obtaining sexually mature males
throughout the breeding season. He described the ease with which they could be caught
and used early in the season, but by the end they were spent leaving several female fish
unfertilized. Therefore large populations of males are necessary to support a hatchery
production system so that this does not occur. Environmental control should also be
used for males retained indoors. The shortage of males demonstrates the need for more
work on the cryogenic preservation of sperm, first developed for fish by Blaxter (1953),
and followed by Hwang, Cheng, Lee & Liao (1972) and Chao, Cheng & Liao (1974) for
the males of Mugil cephalus. Unpublished work by Watters in Hawaii demonstrated the
differences in activity of sperm in a number of media. The motility and viability of the
sperm suspended in ambient sea water (32‰) lasted for about one hour and much
longer than that in other media. However, there were differences between sperm of
different males.
These factors demonstrate once more the need to define the quality of eggs and
sperm from mature fish, and to establish that the quality is maintained year by year. Fish
tend to get treated as part of a population, used and returned to the group. The first
process of marking or isolating good breeding fish can commence now without waiting
for the biochemistry of egg quality to be established. Much fundamental work is possible
now which will lay the foundation for improvement by genetics and stock selection.
The Mugilidae have the greatest potential for becoming the most important
supplier of aquatic animal protein for mankind. However, this potential can only be
realised by the successful artificial propagation of juveniles from hatcheries. The wealth
of information that is available on the culture of the mullet is more than enough to justify
the establishing of a coastal hatchery for the pilot scale production of juveniles. Many
enterprises have succeeded with much less basic knowledge and with less at stake.
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18 (1), 3-13.
Yashouv, A. (1969). Preliminary report on induced spawning of Mugil cephalus L. reared
in captivity in fresh water ponds. Bamidgeh 21 (1). 19-24,
Yashouv, A. & Ben-Shachar, A. (1967). Breeding and growth of Mugilidae. II. Feeding
experiments under laboratory conditions with Mugil cephalus L. and Al capito
Cuv. Bamidgeh 19 (2/3), 50-66.
Yashouv. A. & Berner-Samsonov, E. (1970). Contribution to the knowledge of eggs and
cany larval stages of mullets (Mugilidae) along the Israeli coast. Bamidgeh 22
(3), 72-89
Yoshioka, H. (1962). On the effects of environmental factors upon the reproduction of
fishes. I. The effects of day-length on the reproduction of the Japanese killifish
Oryzias latipas. Bull. Fac. Fish. Hokkaido Univ. (13), 123-36.
Zismann, L , Berdugo. V. & Kimor, B. (1974). The food and feeding of early stages of
grey mullets in the Haifa Bay region. In Proceedings of the IBP/PM International
Symposium on the Grey Mullets and their Culture, Haifa, 2-8 June 1974.
Zviagina.O. A. (1961). The distribution of eggs of mackerel Pneumatophorus japonicus
(Houttuyn) and mullet (Mugil so-iuy Basilewsky) in Peter the Great Buy. Tr. Inst.
Okeanol. 43, 328-36.
TILAPIA CULTURE
Mr. C. AGIUS
1.
ADVANTAGES
1.1. Resistant to poor water quality and disease
1.2. Tolerant to a wide range of conditions. e.g. salinity, temperature
1.3. Good growth rate
1.4. Can utilize organic, domestic and agricultural wastes
1.5. Relatively easy to cultivate
1.6. Amenable to intensification
2.
DISADVANTAGE
2.1. Prolific precocious breeding. They start breeding while still very young
3.
WATER QUALITY
Parameter
Tilapia
Carp
Trout
Critical NH3 levels
Total (mg/l )
20
10 - 13
2
Critical CO2 levels
(mg/l)
73
Critical O2 levels
(mg/l}
15 - 20
0.1 - 3.0
3.0
4.0
Temperature (° C)
8-42
6-40
2 - 23
Salinity (‰)
0-45
12.5
15.0
13,000
190
15.0
Turbidity tolerance
(mg/l)
3.1. Temperature
8° - 10° C
Lower lethal limit (not surviving for very long)
10° - 15° C
Survival but no growth
15° - 20° C
Poor growth
20° - 35° C
Range of significant growth
25° - 30° C
Optimum temperature
25° - 35° C
Preferred range
45° C
Upper lethal limit (decrease in growth)
Overwintering necessary in certain cases
Under 15° C avoid handling (very susceptable to disease caused by brusing on the skin
3.2. Salinity
Tolerance species dependent
Species
Growth
Reproduction
S. niloticus
up to 25 ‰
up to 25 ‰
S. aureus
up to 40 ‰
up to 19 ‰
S. spilurus
up to 40 ‰
_
S. mossambicus
up to 40 ‰
up to 40 ‰
T. zillii
up to 44 ‰
up to 39 ‰
Some species grow faster in salt water than in fresh water. Fecundity is slower,
so not as many fry is obtained in salt water, and sometimes, the salinity stops
reproduction.
4. RED TILAPIA
So called because of its red colour and absence of a black peritoneum (The flesh
is red all through)
It is similar to bream Chrysophrys major
It is the progeny of a O. niloticus x O. mossambicus (mutant) cross.
At 15 - 20 g, it can be transferred to full strength sea water over a few days.
5. GROWTH
Males grow faster than females stunting can occur in ponds
Species
Max. size
(male fish)
Growth rate
S. niloticus
50 cm (3 Kg)
400-600 g/year
S. spirulus
38 cm (1 Kg)
4-5 cm/month
slows after 3 - 4 months
S. mossambicus
2.9 Kg
150 - 350 g/year
6. REPRODUCTION
Problems :
i)
males agressive/territorial presents problems in hybrid crossing
ii) precocious maturity in reared fish
Some figures relating to reproduction are given below :
REPRODUCTION
Species
S.aureus
S. niloticus
S. spirulus
S. mossambicus
Age/size at Size of spawn Frequency of
first spawning
spawning
9 - 12 m 300 - 2,000
8-10 cm
4-5m
300 - 3,500
10 - 17 cm (up to 700 br
ooded)
4m
100 - 600
10 - 14 cm
2-3m
75 - 1,000
6-8 cm
Days to
hatching
days of
hatching
parental care
7-8
8-10
3m
5-8
4-6
3-6 weeks
2-5
14 - 21
2-3m
4m
With mouth breeders (Sarotherodon), there is a difference between the number
of eggs they lay and the actual number hatched. So Niloticus may lay up to 3,500 eggs
but hatch only 700. Mossambicus start spawning at a much younger age and so their
spawning rates are fairly low. This causes quite a number of problems.
7. CONTROLLED FRY PRODUCTION
Normal requirements
i)
Sufficient number
ii) Graded size groups
iii) All male
8. MANAGEMENT OF BROODSTOCK
8.1. Temperature 23° C and higher must be respected
i)
Equatorial regions-production continuous
ii) Sub-tropical and high altitude tropical regions-production restric-ted to
warmer months.
Thermal shock can induce spawning
e.g. : S. niloticus
2 weeks at 18° C
Transfer
25° C - Spawning occurs
Some species are very sensitive to temperature, in terms of reproduction, even if
they are within the preferred limits of reproduction, Ex. With Spilurus, even though you
may be well over 25° C, if the temperature has regular changes between 25 - 35°C, the
rate of reproduction slows down and so less spawnings are obtained.
8.2. Salinity
–
Above 20 ‰ fecundity decreases
–
CouId be advantageous
Maximum for fry production
S. aureus 4 - 5 ‰
- S. mossambicus 10 - 13 ‰
8.3 Food
The feeding of the broodstock is fairIy straight forward, using a 35 - 40 % protein
content diet. This is optimal rate. The Feeding of broodstock is very important because
of this territorial behaviour and to stress must be caused to the fish. Thus overcrowding
should be avoided while at the same time as many broodstock as is possible must be
employed so as to obtain the desired number of fry/m2.
High stocking density depresses spawning
Exploitable but problematic for large scale fry production
2 factors must be considered :
i) Broodstock density
)
)Optional values not yet known
)
ii) Sex ratio
Some examples
Species
Location
S. aureus
S. niloticus
S. aureus
S. mossambicus
Baobab
Kenya
Alabama
Hawaï
S. hornorum
Brazil
Stocking rate
Number/m2
Ratio
2
1:6
10
13
1:3
1:3
0.04
1:3
Average wt.
(gms)
Fry production
n/m2/month
♂ 250 - 500
♀ 80 - 200
Approx. 100 -250
♂154
♀ 134
♂90
♀ 45
200
200
400 - 750
250 - 400/♀
9. PRODUCTION OF ALL MALE FRY
9.1. Hormone treatment
Androgens : 17 ∞ -methyltestobterone (MT)
Genetic females → functional males
Genotypic males : unaffected
Administration : via food 30 - 60 mg/kg of food from 3/7 days post-hatching ( 5 - 11 mm)
for 20 - 40 days
Drawback : sex-reversed males are slower growers
9. 2 . Hybrid crosses
Crossing of genetically pure stocks
All male progeny
Fish have to be netted out every 3 months to avoid back crossings.
Some examples
Female parent
S. aureus
S. niloticus
S. niloticus
S. vulcani
Male parent
S. hornorum
S. hornorum
S. aureus
S. aureus
% male progeny
90 - 100
98 - 100
50 - 100
80 - 100
such handling reduces reproductive capacity
Problems
Difficult to maintain purity of stocks, selection of pure stocks time consuming,
lower fecundity (56 %) of hybrid crosses.
9.3. Intensive selective grading
Continuous selection for faster growing males (at least every month}
10 FRY PREFATTENING
Range of conteiner designs endless e.g. raceways, square tanks, circular tanks.
Open system rate : 0.5 - 1.0 l/kg/min
Current speed :
lowest 10 cm/ sec.
highest 25 cm/sec
Diameter : depth 5 - 10 : 1
For raceways : shallowness recommended
d = Working depth (metres)
F = Flow rate m3/hr (depends on oxygen requirements)
A = Area of raceway (m2 )
R = Number of water changes/hr
Typical stocking programme :
Stock 20 - 40 g fingerlings at 500 - 1,000/m3 i.e. 20 Kg/m3
Feed at 2.5 - 4 % body wt/day (25 % protein FCR 2 - 2.5)
Should reach 200 gm in 120 - 150 days
3 harvest/year possible
13. NUTRITION
There is no standard tilapia diet. Formulations largely based on locally available
raw materials
General protein requirements :
1g
35 - 50 %
1-5g
30 - 40 %
5 - 25 g
25 - 30 %
25 g
20 - 25 %
A certain minimum level of animal protein seems to be needed.
Essential amino-acid requirements similar to carp and trout
Fat and carbohydrate requirements poorly known.
Pellet sizes - Powdered diets - first feeding
Wean on to granular food,
Then 3 mm size pellets.
Tilapia have no stomach, therefore they feed several times per day.
11. STOCKING RATES
Some realistic production values in intensive systems :
Size
Number of fish/m3
Wt/fish
Stocking density
1-5g
1,600
1.6 - 8 Kg/m3
Prefattening
10 - 20 g
1,000
10 - 20 Kg/m3
*½ Fattening
25 - 50 g — 250 g
200
50 Kg/m3
(final)
Fry
* 1. Allows for enhanced individual growth rates to produce larger fish
* 2. Faster growing 50 % are ongrown (70 % males)
2 harvests a year
Slow growers Find alternative use
12. CAGE CULTURE
Curbs reproduction. Can. resuit in food losses. A variety of species have been
tried.
Range of recorded yields under experimental and commercial conditions :
Species
S.aureus
S.niloticus
S.gairdneri
C.carpio
Yields
(Kg/m2)
17 - 94
35 - 76
4 - 118
10 - 190
Conversion ratio
W = Final biomass (Kg)
A
= Cross-sectional area of submerged part of cage (m2 )
F
= Water current (cm/min)
DO = Dissolved O2 (mg/l)
1.2 - 3.1
1.2 - 3.7
1.6 - 2.0
1.6 - 2.5
r
= Respiration rate (mg/kg/min)
3.0 = Lower lethal O2 tolerance limit i.e. level below which productivity is
retarded.
CONTENTS
1. Advantages
2. Disadvantages
3. Water quality
3.1
Temperature
3.2
Salinity
4. Red TiIapia
5. Growth
6. Reproduction
7. Controlled fry production
8. Management of broodstock
8.1
Temperature
8.2
Salinity
8.3
Food
8.4
Stocking density
9. Production of all male fry
9.1
Hormonetreatment
9.2
Hybrid crosses
9.3
Intensive selective grading
10.
Fry prefattening
11.
Stocking rates
12.
Cage culture
13.
Nutrition
SOME SELECTED REFRENCES ON TILAPIA CULTURE
BALARIN, J.D. and R.D. HALLER (1982). The intensive culture of Tilapia in tanks,
raceways and cages. In : Recent advances in Aquaculture - Muir,
J.F..and R.J. Roberts (editors). Croom Helm Ltd - pp. 267-355.
BALARIN, J.D.and HATTON, J.D. (1979). Tilapia : A guide to their biology and culture in
Africa. Unit of Aquatic Pathobiology, STIRLING University, 174 pp.
FISHELSON, L. and Z. YARON (eds/1983). International Symposium on Tilapia in
Aquaculture. Proceedings of the Nazareth Conference, May 8 - 13 1983.
622 pp.
LARVAL REARING, WEANING AND FIRST FATTENING OF SOLE AND TURBOT
Mr. B. MENU
1. THE SOLE (Solea vulgaris)
1.1. Larval rearing
The larva of the Sole is "fat" when hatched with a size of 3,6 mm and a weight of
0,6 mg., it can feed on Artemia nauplii as soon as it's mouth opens. (FUCHS, 1982)
(Figure 1).
Larval rearing does not cause any particular problem, the metamorphosis takes
place quickly (after 15 days at 18° C), the survival rate is high (60 to 80 %) and the
growth rate is good (70 mg after 30 days at 18° C).
However the success of larval rearing depends entirely, from the beginning, on
the quality of the Artemia, the composition of which can not, at nauplii stage, be modified
before distribution. Then is remarked abnormal pigmentations in some populations and
at present although the causes of the abnormalities have been dealt with (LEBEGUE,
1982), the problem has not been clarified.
1.2. Weaning
Weaning had been considered a major problem for a long time in the intensive
rearing of Sole.
The research carried out by FUCHS (1981, 2) shows a clear difference for
survivals obtained while employing natural inert food (70 %) or dry compound food (40
%).
METAILLER et al (198l) also showed that the presence of natural appetizing
ingredients in the diet mixture had a beneficial effect when the weaning was carried out.
Great progress was made in 1982 when the chemical ingredients (Betaine - Glycine Inosine) were employed as an appetizer in the rehydratable pellet food (CADENA ROA
et al. 1982).
The survivals and growth rates obtained with this type of diet mixture are
comparable, it( not better, than those obtained with natural food. The weaning of Sole in
intensive rearing conditions is no longer a limiting, factor for the rearing development of
the species. However, like that, of the sea-bass, this phase is still delicate and from time
to time accidents can occur.
It must be remarked that early weaning were performed while employing a mixed
diet for the larvae of Sole and interesting results for both survival and growth were
obtained (GATESOUPE, 1983).
1.3. First fattening
First fattening is still the principal obstacle in intensive rearing. From one
population to another of juveniles, results can vary a lot whatever the food employed
(Figure 2 ) and in almost all cases, the growth in intensive rearing can not be compared
with that obtained in extensive rearing in a rich natural environment (BARRET et al,
1981) (Figure 3).
In his thesis on the intensive rearing of Sole, P. MORINIERE (1983) concluded in
the following way : "Research should be concentrated, in particular on first fattening, the
duration of which appearing to have an influence on the time required for commercial
size to be reached".
This research work remains to be looked into.
1.4. Present Production
At present there exists no large scale production of Sole fry nor intensive farm
production of Sole to commercial size.
Actually only small scale experimentations are remarked in certain laboratories
which have stocked a few batches of spawners.
It is surprising that with such a species, when it is so easy to produce juveniles,
development has not been achieved more rapidly. The obstacles, stated here above in
intensive first fattening, have certainly not yet been overcome, but the absence of
extensive rearing tests performed with the necessary means, is, as for as I am
concerned, a grave error.
2. TURBOT (Psetta maxima)
2.1. Larval rearing
When hatched the larva of the Turbot measures 2,7 to 3 mm and weighs around
0,15 mg. On account of its size and weight, the Turbot larva heads the list in front of the
Sole and Sea-bass larva and is at around the same level as the Gilthead sea-bream
larva.
Rotifers are distributed for the first two weeks in rearing (at 18° C) while taking
into account the small size of the larvae when they start feeding (Figure 4).
As for the Sole, the growth rate of Turbot is strong during the first month and
average weights of 75 mg are reached by the 30th day at 18° C. The metamorphosis
does not occur as soon as for the Sole and is only completed after 40 days at 18° C.
The first work carried out on the larval rearing of Turbot in Great Britain, and then
in France brought about the development of two techniques :
–
Initially small rearing loads were placed into big tanks having green water.
–
Greater rearing loads were placed into smaller tanks having clear water.
The first method in green water having not evoluted with time, we were interested
by the method in clear water, which is the most employed, especially taking as example,
the evolution of the techniques perfected in France in the IFREMER laboratories and
farms.
In 1980, GATESOUPE (1982) demonstrated the beneficial effect on survival and
growth of the Turbot larva, by enriching the live prey just before distribution, with nutritive
ingredients and antibiotics. These works, completed by those of LE MILINAIRE (1984)
permit the definition of the quantitative requirements of the essential fatty acids (w 3) for
the larva and juvenile of Turbot - Respecfully 1,2 % and 0,6 % in dry weiqht of the prey.
The application of these enriching methods at pilot production scale gives good
results at first, then little by little, a decrease in the average survivals is remarked (Figure
5) both at the laboratory and in the pilot facilities.
The change of the enrichment formulas of live prey, the change in the conditions
of temperature,salinity and lighting and the addition of Copepoda hove brought no
solution to this problem.
The quality of the Turbot larva does not seem to be the cause. However, the
sensitiveness of the Turbot larva towards the bacterial environment and the analogy
which can be tried out with difficulties of the same type, occuring in larval rearing of
tropical shrimp (AQUACOP, 1979) have caused research to be directed towards the
improvement of the sanitary management of both larval and prey rearing and already
some encouraging results have been obtained.
The works carried out in the laboratories and pilot facilities, over these past years
have permitted the definition of certain original points of the Turbot larva biology at
feeding level (GATESOUPE et al, 1984) or at bacterial flora level associated with rearing
(NICHOLAS et al., 1986 - ROBIC, 1985).
Therefore, there is a hope that there will be a quick outcome to these research
works. However, at present, the juvenile production of Turbot is still a limiting factor for
the industrial rearing development of this species, as is the case for Gilthead sea-bream
rearing.
2.2. Weaning
Like for the Sole, the weaning of the Turbot was developed in 1982 with the
perfection and test on important quantities of rehydratable food containing lnosine as the
appetizing ingredient (J. PERSON LE RUYET et al, 1983).
However, it must be remarked that the weaning of the Turbot is easier than that
of the Sole. Again, the behaviour of the Turbot at this stage is similar to that of the
Gilthead sea-bream, while not taking into account the problems of cannibalism which are
rarely remarked with the Turbot juvenile. Survivals of 60 to 90 % are generally obtained
for the weaning of juveniles having a average weight of 150 mg., and it must be
remarked that the differences noted in the success of this operation are due to both the
type of food employed and the quality of the Artemia used before weaning (BROMLEY
et al, 1983). GATESOUPE (1982) also shows that the type of enrichment used for the
live prey-in larval rearing has on influence on the growth after weaning.
2.3. First fattening
Intensive first fattening of Turbot does not cause any particular pro-blem, the
results for growth (Figure 2) and for survival are good and quite the same when
compared to the one another which shows that this phase is well in control .
However, for fish of less than 5 g. (4 months at 18° C) their sensitiveness to
Vibriosis is strong and this disease can cause great losses, no matter what curative
treatment is used. To avoid the development of outbreaks, prophylactic measures with
the aim of limiting the source of the contamination, the Ultra violet treatment of the seawater for example, are often effective but the use of a vaccine by intraperitoneal injection
can alone ensure the final protection of the population. This vaccination can be carried
out on juveniles whose weight does not exceed 0,5 g (2 months at 18° C).
Large loads of Turbot may be employed in first fattening without causing any
effect to their growth, they can also support easily manipulation (no scales) and
transport.
2.4. Present production
The growth potential of the Turbot (Diagram 6) and the encouraging perspectives
of the market have caused many European countries to try out experimentally intensive
rearing.
Production farms of Turbot at pilot stage or commercial facility stage can be
found.
–
In Great Britain ( Especially SW of Scotland}
–
In France (The Channel and Atlantic Coast.)
–
In Norway
–
In Danmark
–
In West Germany
–
In Spain (Galicia)
At present, it is the Golden Sea Produce, at HUNTERSTON (Great Britain.)
which holds the production record, with 130 000 fry produced and 50 ton commercialized
in 1985. The total European production for 1985 is around 100 ton approximatively. This
is still very average and a reliable technique for fry production is still needed so that a
significant increase in tonnage may be obtained.
Figure 1 : Live prey feeding for sole larvae during the first month of rearing (from J.
PERSON LE RUYET)
Figure 2 : Growth curves in intensive rearing of Sole and Turbot (0 - 18° C)
Maxi : A
Mini B
According to J. PERSON LE RUYET, 1985
Figure 3 : Growth rates of Sole in Intensive and extensive rearing in similar conditions of
temperature and photoperiod Survival of 1 month, at 200 g :
–
Intensive 30 %
–
Extensive 5 %
According to BARRET, 1978 and MORINIERE, 1983
Figure 4 : Live prey feeding for Turbot larvae during the first month of rearing (From J.
PERSON LE RUYET)
Figure 5 : Average results of production in larval rearing (mini- average- maxi) at the
SODAB Hatchery for Turbot since it was started.
Figure 6 : The comparison of growth rates of some marine fish and salmonids in
intensive rearing and natural temperature
CONTENTS
1.
2.
The sole (Solea vulgaris)
1.1.
Larval rearing
1.2.
Weaning
1.3.
First fattening
1.4.
Present production
Turbot (Psetta maxima)
2.1
Larval rearing
2.2
Weaning
2.3
First fattening
2.4
Present production
BIBLIOGRAPHY
–
AQUACOP, 1979
About the concept of crowding disease and sanitary lot in modern intensive
aquaculture : a short note. Proceedings of the 10th annual meeting of the W.M.S.
HONOLULU - January 1979 - p. 551 - 553
–
BARRET, J. and M.J. MATRINGE, 1981
Comparaison of growth of Sole in intensive rearing with moist food versus in
extensive rearing in coastal pond. Congrès W.M.S. VENISE, 198l
–
BROMLEY, P.J. and B.R. HOWELL, 1983
Factors influencing the survival and growth of Turbot larvae during the change
from live to compound feeds. Aquaculture, 31 - p. 31 - 40
–
CADENA ROA, M., C. HUELVAN, Y. LE BORGNE, R. METAILLER, 1982
Use of rehydratable extruded pellets and attractive substances for the weaning of
Sole. J. World Mariculture. Soc. 13, p. 246 - 253
–
FUCHS, J. 1982 - 1
Production de juvéniles de Sole en conditions intensives. Le premier mois d' é
levage. Aquaculture 26, p. 321 - 337
–
FUCHS, J., 1982 - 2
Production de juvéniles de Sole en conditions intensives. 2. Techniques de
sevrage entre 1 et 3 mois. Aquaculture, 26, P. 339 - 358
–
GATESOUPE, F.J. , 1982
Nutritional and antibacterial treatments of live food organisms : the influence on
survival, growth rate and weaning success of Turbot. Ann. Zootech. 1982, 31 (4),
p. 353 - 368
–
GATESOUPE, F.J., 1983
Weaning of Sole before metamorphosis achieved with high qrowth and survival
rates. Aquaculture, 32, 4, p. 401 - 404
–
GATESOUPE, F.J., J.H. ROBIN, C. LE MILINAIRE, E. LEBEGUE, 1984
Amélioration de la valeur nutritive des filtreurs proies par leur alimentation
composée. In Aquaculture des Bars et des Sparidés, INRA, Pub. PARIS 1984, p.
209 - 222
–
LEBEGUE.E., 1982
Etude morphologique et expérimentale sur la pigmentation de larves et juvéniles
de Soles et de Turbots. Thèse 3ème cycle, Univ. Bretagne Occidentale, 165 p.
–
LE MILINAIRE, C. 1984
Etude du besoin en acides gras essentiels pour la larve de Turbot pendant la
phase d'alimentation avec le Rotifère. Thèse 3ème cycle. Univ. Bretagne Occidentale.
167 p.
–
METAILLER, R., B. MENU et P. MORINIERE, 1981
Weaning of Sole using artificial dies. J. World Maricult. Soc. 12 (2) p. 111 - 116
–
NICOLAS, J.L., JOUBERT M.N., 1986
Bactéries associées aux productions de Brachionus plicatilis - GERBAM
Deuxième colloque international de bactériologie marine - CNRS - BREST -1-5 oct.
1984 - IFREMER - Actes des colloques, 3, 1986, pp 451 - 457
–
PERSON LE RUYET, J., B. MENU, M. CADENA ROA, R. METAILLER, 1933
Weaning Turbot on dry rehydratable pelleted foods. Presented at World
Mariculture Society meeting. WASHINGTON D.C. January 9-13, 1983
–
ROBIC, E. 1985
Etude simultanée de microflores associées à trois niveaux d'une chaîne
alimentaire d'aquaculture : Algues microphytes, Rotifères, Larves de Turbot. Rapport
DEA d'écologie microbienne, Univ. PARIS Sud, 32 p.
FRY PRODUCING TECHNIQUES OF RED SEA BREAM, Pagrus major, IN JAPAN
Mr. C. KITAJIMA
Red sea bream, or Madai in japanese, Pagrus major (TEMMINCK et
SCHLEGEL.) is distributed from the coastal waters around Japan down to the East
China Sea and Southeast Asian waters. It grows up to about one meter TL, and is one of
the most important and expensive fish in Japan for its delicate flavour and elegant
appearance, and often used in various festival occasions such as weddings, birth-days,
new year parties and festivals.
The annual catch of red sea-bream in the coastal waters around Japan is about
20 000 ton, but recently its natural stock reveals a tendency to decline.
Culture of this fish using the wild fry started in around 1965 and soon became
very popular in the southwestern waters of Japan. Since about 1975, the seed
production of this species in hatchery has developed rapidly, and the number of fry
produced at hatcheries in the whole country reached 40 millions in 1983 (Fig. 1). At
present, the greater part of the seed for culture is taken up by hatchery-produced ones.
On the other hand, the experimental projects to stock with fry the coastal waters
in order to promote the coastal fishery started in 1975.
At present, in Japan, in addition to 13 national hatcheries and 40 prefectural
hatcheries, several scores of hatcheries are run by private sectors.The fry for stock is
mainly produced in the governmental hatcheries, while the seed for culture in private
hatcheries. The numbers of fry stocked and cultured in 1983 were 23 millions (at 39
hatcheries) and 16 millions (at 32 hatcheries), respectively. (Fig. 1 and 2)
Although the initial trial of seed production of this fish was carried out by
KAJIYAMA and his coworkers in 1917, the full-scale studies started in the late 1950 s.
Therefore, the history of fry production dates only 25 years back and many problems still
remain to be resolved.
1. PARENT FISH AND EGG SUPPLY
1.1. Parent fish
At the early stage in the development of culture techniques, eggs and sperm
were taken from wild female and male by means of the so-called "stripping method".
Nowadays, the fertilized eggs are collected from a tank, in which parent fish spawn
In captivity, this fish sexually matures in the second or third year of age. The
biological minimum of female is about 30 cm in total length and 500 g in body weight
(KITAJIMA, 1978), but most suitable as parent fish are those of 1 to 3 kg (3 to 5 years).
The culturing methods of parent fish is similar to those of ordinal commercial
culture ; they are put in a net cage attached to a raft in a bay and fed artificial feed fresh
or frozen fish such as sardine, anchovy, horse mackerel and krill.
1.2. Egg supply
The spawning season of this species extends from April to July, when the water
temperature ranges from 15 to 22° C.
The parent fish, which are ready to spawn, are transferred from a net cage to a
spawning tank on land. A density of parent fish in a spawning tank is one fish per ton,
with females and males in the same number. It is easy to determine the sex as a male
becomes partly black in spawning season.
A female of 1 kg in body weight lays 50 000 to 100 000 eggs at about sunset
everyday for 50 days or more. The total number spawned by a female of 1, 1,5 or 2 kg in
a season reaches 3 000 000, 5 000 000 and 9 000 000 respectively (KITAJIMA, 1978)
(Fig. 3, fig. 4).
The eggs are collected by a small-meshed net which has been fixed at an
overflow outlet of the tank. We can estimate the number of eggs collected from the
weight, one gram contains about 1 800 eggs.
Normal eggs are buoyant, while unfertilized and undeveloped eggs are settled
like in incubation. So, the rate of buoyant eggs against the total number indicates
roughly the quality of eggs spawned.
The weight of all the eggs spawned by a female for a season reaches 1.5 times
its own body weight, accordingly it is necessary to feed sufficiently parent fish everyday.
Recent studies reveals a close relation between the nutrients of a diet for parent
fish and the quality and quantity of eggs spawned. Further studies in this field is required
(WATANABE et al., 1984 a, b, c ; 1985 a, b).
There are several trials so as to speed up or lengthen the spawning season by
controlling the water temperature of the rearing tank.
2 . LARVAL AND JUVENILE REARING
2.1. Outline of rearing.
Early growth of red sea bream is as following (KITAJIMA, 1978)
Developmental stage
Age in day
Total lenght
Larval stage
Prelarval stage
Post larval stage
Juvenile stage
0 -- 3 to 5
-- 25
-- 60
2.3 -- 3.0 mm
-- 10
-- 40
The fish of late juvenile stage, 40 mm in size is suitable for both culture and
restocking.
Larvae fish are planktonic and scatter all over the tank, and they are reared at as
high a density as 20 000 to 30 000 per ton. At juvenile stage, they settle down to the
bottom of the tank and their swimming ability increases remar-kably. The inclination to
bite one another and cannibalism also begin at this stage. Therefore, it is necessary to
rear juveniles in a lower density and in a wider space area.
Larvae are mainly fed on live organisms such as rotifers and Artemia nauplii,
while juveniles are generally given inert feed, such as artificial feed and minced fish
meat, so the contamination of rearing water becomes often serious at the stage.
Accordingly, it is generally adopted that larval fish are reared in a tank, and they are
transferred to a net cage in the sea at juvenile stage of 12 to 13 mm in size.
2. 2. Larval rearing in tanks
The fertilized eggs are put into a rearing tank which contains 50 to 100 tons of
seawater, at a rate of 20 000 to 30 000 eqgs per ton. The eggs are incubated in this tank
under gentle aeration with 10 to 15 airstones.
Hatching occurs in 50 hours at 18° C and in 40 hours at 20° C after spawning.
The newly hatched larvae are about 2.3 mm TL and live on the yolk for 4 to 5 days at a
temperature of 18° C.
During the first week or ten days after hatching, we do not change the water in a
rearing tank. Thereafter, the filtered seawater is supplied to a tank. Towards the end of
larval rearing, the water supplied is that of the capacity of the tank or a little less per day.
In the case of an outdoor tank, it is covered with a layer of shade netting to
reduce the maximum light intensity to about 5 000 lux at the water surface.
2. 3. Juvenile rearing in net cages
At a conveniently located hatchery, larvae are siphoned out from the tanks to net
cages. A cage size is ordinally 5 by 5 by 3 m. The 12 - 14 mm juveniles are stocked at a
density of 2 000 to 3 000 per cubic meter in a 2 mm-mesh-caqe. As the juveniles grow,
their density is reduced by transferring them to new cages of larger mesh every 7 to 10
days.
2. 4. Growth
The growth of larvae and juveniles is closely related to the water temperature.
For example, at 20 - 23° C, the newly hatched larva is 2.3 mm TL ; 4.4 mm in 10 days ;
8.1 mm in 20 days ; 14.8 mm in 35 days ; 23,7 mm in 42 days ; 41.3 mm in 56 days (Fig.
5 KITAJIMA, 1978).
The relationship between the total lenght (L mm) and wet body weight (W mg) is
shown in the following equations (KITAJIMA, 1978).
W1 = 0.0013 L 4.1045 (3.75 mm< L< 6.75 mm)
W2 = 0. 0038 L 3.5486 (6.75 mm< L < 10.25 mm)
W3 = 0.0154 L 2.9735 (10.25 mm< L<42.5 mm)
W4 = 0.0091 L 3.4078 (42.5 mm< L<85 mm)
2.5. Survival rate
Although the survival rate is nearly 100 %,10 days after hatching, about 5.5 mm
in size, after that the mortality increases remarkably and continues for 30 days, 12-13
mm Tl. Thereafter, the mortality drops gradually and after 50 days, around 25 mm TL,
the survival rate is stable at 80 % or more (Fig 5, KITAJIMA, 1978).
Thus, the stage of high mortality, the critical period is 10 to 50 days old of 5.5 to
25 mm TL, especially it is higher in the period between 10 and 30 days, 5.5 mm and 13
mm, and this period corresponds to the metamorphic stage from larval to juvenile stage.
In the recent hatchery-production, the survival rate is 40 to 50 % during larval
rearing in tanks, 50 to 60 % in the juvenile rearing in net cages and 20 to 25 % through
the whole process, although there is a little difference among hatcheries.
2.6. Larval and juvenile feed
2.6.1. Sequential change of larval and juvenile feed
For ten years, from the mid fifties to 1965, research work was carried out to find
the suitable diet for larval fish, and many species of micro-crustacea, larvae of the
coastal invertebrates and artificial diets had been tested for their dietary value for larval
fish.
After passing through this feed-research period, at present, a series of generally
adequate diets for larval and juvenile fish of most species is almost fixed as follows :
1) The post-larvae from 4 to 30 days after hatching are fed on mass-cultured
rotifers.
2) The metamorphic stage larvae are fed on rotifers combined with crustacean
plankton such as Artemia nauplii, cultured Tigriopus japonicus, and copepods collected
in the natural environment.
3) Juvenile fish are fed on inert feed such as minced fish, shellfish and shrimp
meat, or artificial feed.
2.6.2. Daily feed consumption and feed supply
It is important to know the amount of live feed consumed by a single larva per
day at each stage of the sequential growth in order to mass-produce and supply
systematically the suitable amount of live feed.
If the number of larvae and the density of the feed organisms in the tank were
known, the daily feed consumption by a larva could be calculated through a sequential
decrease of the density of feed organisms.
The relations between the number of rotifers (R) or Tigriopus japonicus (T) eaten
by a larva per day and the larval total lenght (L mm) are shown in the following formula
(KITAJIMA, 1976 ; KITAJIMA et al, 1976).
R = 0.3927 L 3.675 and T = 0.06728 L 3.466 (Fig. 6, 7)
The average weight of an individual rotifer was 0.003 mg and that of a T.
japonicus was 0.034 mg, in these experiments, therefore the consumed amount is
roughly 60 % of the larval body weight in a common wet basis, at each stage.
Furthermore, the rotifer density in a rearing tank has to be maintened always at
least at 5 individ./ml to avoid larval starvation and to make fewer deviations in larva!
growth. It is estimated that the necessary feed amount of live feed is 1.3 to 1.5 times that
of the amount eaten by larvae when taking into consideration the outflow of organisms
with the circulation of water. FUSHIMI (1977) found that the growth and the survival rate
of red sea-bream larvae were unchangeable even if the daily amount of rotifer given was
more than 80 % of body weight.
2.6.3. Dietary value of living organisms
At the early developmental stage of the culture techniques before 1972, only
marine Chlorella was used as a culture diet for rotifer. With the increase of production of
red sea-bream seed, the amount of rotifers required has become. enormous and baker's
yeast was subtituted instead of marine Chlorella. As a result,. the culture density of
rotifers increased from 30 - 50 to 100 individ./ml or more.
Although the red sea-bream larvae with the rotifers reared on Chlorella
(Chlorella-rotifer) grew normally, serious mortality was observed in the larvae fed on the
rotifers reared on baker's yeast (yeast-rotifer) alone for 10-15 days. It was then found
possible to prevent this mortality by feeding yeast-rotifer with marine Chlorella
secondarily for several hours or rotifers reared on baker's yeast in combination with
marine Chlorella (KITAJIMA and KODA, 1976).
From the results, chemical analyses on both yeast and Chlorella- rotifer were
conducted by our coworkers in order to clarify their nutritional value. As there was little
difference between the amino-acid and mineral composition of both rotifers, it seemed
that they were not principal factors in the dietary value (WATANABE et al., 1978 a, 1978
b). On the other hand, it was found that there were marked differences in the fatty acid
compositions of them, i.e. yeast-rotifer was quite low in the content of w3 highly
unsaturated fatty acids (w3 HUFA). such as 20 :5 w3 (eichosapentaenoic acid) and 22 :
6w3 (dochosahexaenoic acid), which are essential fatty acids (EFA) for marine fish
(YONE and FUJII, 1975 a, 1975 b ; COWEY et al., 1976), whereas Chlorella rotifer was
found to contain a high amount of 20 : 5w3. The difference in the concentration of 20 :
5w3 was also found to be attribuable to the difference of the fatty acid composition
between yeast and Chlorella (WATANABE et al., 1978 c) (Table 1).
A trial was conducted in order to improve the low dietary value of yeast rotifer by
feeding them marine Chlorella for 10 min. over 24 hours at regular intervals before being
given to red sea-bream larvae. The dietary value of yeast-rotifers was found to be
improved effectively by the secondary culture. with Chlorella. The larvae fed on yeastrotifers cultured secondarily for more than 6 hours showed good results and a high
survival rate, comparable to those obtained with the larvae fed on Chlorella rotifers
(Table 2, KITAJIMA et al., 1979 ; WATANABE et al., 1979).
When marine Chlorella was used as a culture medium, the quite low content of
w3 HUFA in rotifers reared on baker's yeast increased in proportion to the culture period
by the incorporation of 20 : 5w 3 from marine Chlorella, and reached a maximum at 27
% in a two-day-feeding (WATANABE et al., 1979).
These results indicated that the content of w3 HUFA in the rotifers was the
principal factor in the dietary value of them and that the high mortality observed
frequently in red sea-bream larvae induced by feeding them yeast-rotifers as their sole
feed was due to EFA deficiency in the fish.
With these results, a new type of yeast (designated as w yeast) was produced by
adding fish oil or cuttlefish liver oil as a supplement to the culture medium of baker's
yeast, resulting in a high concent of lipids and w3HUFA (IMADA et al., 1979)- The
rotifers cultured with wyeast had high lipid content and w3 HUFA. The incorporation of
w3 HUFA from wyeast was observed to reach its maximum after 12 h-feeding. The
dietary value of the rotifers for fish larvae was found to be significantly improved,
comparable to that of Chlorella-rotifers (KITAJIMA et al., 1980 a) (Table 3,4 ; Fig. 8, 9).
The same results as obtained in red sea-bream were found in several species of
marine fish larvae, such as rock bream, Oplegnathus fasciatus (FUKUSHO et al., 1978),
puffer, Takifugu rubripes (ARAKAWA et al., 1978) and ayu, Plecoglos-sus altivelis
(KITAJIMA et al., 1980 b).
Furthermore, the content of w3 HUFA is the most important factor in the dietary
value of not only rotifers but also other live feeds such as Artemia nauplii and copepods.
Especially, a single dosage of Artemia frequently caused a weakening of larvae, and a
consequent high mortality of many species of marine fishes. The occurence of this
phenomenon varied with the species as well as with the place of production of Artemia.
Artemia eggs from different localities were analyzed for fatty acid composition in order to
clarify the nutritional value of Artemia for marine fish larvae (WATANABE et al., 1978 d,
1980 ; FUJITA et al., 1980). From the results shown in Table 5, Artemia eggs can be
classified in two types according to the fatty acid composition (WATANABE et al., 1978
d). One type contains a large amount of 18: 3 w3 (linolenic acid), which is the EFA for
fresh-water fish, whereas the second type is high in 20 : 5w3, which is one of the EFA
for marine fish.
The dietary value of Artemia of the fresh-water type was found to be improved
effectively by giving them feeds with a high amount of w3 HUFA such as Chlorella and
yeast in the same manner as the rotifer mentioned above. Furthermore, it is possible to
improve the dietary value by giving it directly to Artemia in the form of emulsified lipid
with a large amount of w3 HUFA (WATANABE et al., 1982. Such copepods as T.
japonicus and Acartia spp have a large amount of w3 HUFA and arc excellent feed for
larval marine fish.
2.7. Disease
Although the main cause of mortality seems to be infectious diseases and
microparasites, the studies on them have been just started and there are many problems
to be solved. The bathing or oral administration of antibiotics are conducted for bacterial
disease in the larval and juvenile stages.
2.8. Deformity
With the growth of seed-production of red sea-bream, such deformities as shorttail, pughead, incomplete development of gill cover, skeletal abnormalities, etc.. are
observed more or less in the juveniles produced at hatcheries and laboratories. They
become a big problem when they occur in high percentages.
Since around 1973, a high prevalence rate of lordosis, V-shape curvature of
column, had been frequently observed in almost all the laboratories and hatcheries in
Japan. As this happened frequently, 20 to 50 %, it became a severe problem (Table 6).
We had studied the cause of this deformity from 1975 to 1980, and succeeded in
almost clarifying the cause of the deformity.
The lordosis is usually found in juvenile of about 20 mm in size. After that the
occurence and the degree of curvature increase gradually with the growth. After
attaining the lenght of 120 to 130 mm, both the occurence and the degree of deformation
are roughly fixed (KlTAJIMA et al., 1975 ; KITAJIMA, 1977) (Fig. 11 ).
In 1977, it had been revealed that there was a close relation between the lordosis
and undeveloped swim bladder (KITAJIMA et al., 1977) (Fig. 12 , 13.).
Larva! red sea-bream gulps atmospheric gas at the water surface, for initial swim
bladder inflation for about a week between the initial feedinq (ages 3 to 7 days) and
growth to about 4,5 mm (10 to 12 days old) (KITAJIMA et al., 1981). YAMASHITA (1966)
observed histologically that the first gas appeared in the swim bladder of larval red seabream at the age of around 8 days and that the larval pneumatic duct was then closed
and gradually degenerated by the 10 to 12 day of age. Accordingly, the period with the
functional pneumatic duct in the larval stage corresponds with the stage of gulping air
and the resulting initial swim bladder inflation (Table 7 - 8, Fig. 14).
The fish which had failed to gulp air at the water surface for some reason or other
during the stage with the larval pneumatic duct, 3.5 to 4.5 mm in total length, grew
without swim bladder inflation, and as a result the majority of them became lordotic when
they grew to the juvenile or young stage (Fig. 15).
The specific gravity of the individuals with a normal swim bladder is about 1.04,
while that with an uninflated one is 1.07 or so (KITAJIMA, 1978). So, the fish with
uninflated swim bladder (Fig. 16) displayed difficulty in keeping themselves in the upper
or middle layer of the water. They swim upward in an oblique manner with a rapid fin
stroke. The lordosis seemed to be induced when they try to compensate for the oblique
direction of the body axis thus causing a distortion of the spinal column.
The feeding the rotifers with a low content of w-3 HUFA to larvae showed a
tendency to increase the appearance of fish with uninflated swim bladder (KITA-JIMA,
1978; WATANABE, 1978), (Fig. 17). Moreover, ISEDA et al., (1973) discovered that the
proportion of fish with uninflated swim bladders had a tendency to increase in the rearing
tanks with too much aeration (Table 9).
From these results, it is possible to draw conclusions concerning the gulping of
air in larvae as following :
As the larval red sea-bream fed on the rotifers with low content of w-3 HUFA
showed low activity, shortage of endurance and lack of reflex responses, it might be
difficult for them to gulp air after attaining the water surface while at the same time,
having to withstand the current of water caused by the aeration.
In addition to red sea-bream, the same kind of lordosis also occurs in the fish
with uninflated swim bladders in hatchery-reared species such as black sea-bream,
Acanthopagrus schlegeli (KITAJIMA, 1979), common sea-bass Lateo labrax japonicus
(HAYASHIDA et al., 1984) and silver bream, Sparus sarba (KITA-JIMA, unpublished),
and their causes and mechanisms seem to be the same as those of red sea-bream.
3. CULTURE OF LIVE FEEDS
3.1. Culture of rotifer
Twenty years have passed since the rotifer, Brachionus plicatilis, was introduced
as a food organism for marine larval fishes by IT0 (1960). There-after, the technique of
fry production has rapidly progressed together with the advancement of its culture
techniques.
There are. two types of rotifers cultured all over Japan. One called S-type, which
is relatively small (150 urn in lorica length) having its lorica with pointed anterior spines
more curved in shape, while the other, called L-type is larger than S-type (250 urn) and
has a slender lorica with obtuse anterior spines. The former grows actively at higher
temperatures of 20 to 27" C, while the suitable temperature for the growth of the latter is
lower, between 10 to 17° C.
Recent studies have shown that both rotifers are of different genetic strains, and
classified as sub-species; Brachionus plicatilis rotundiformis (S-type) and B. plicatilis
typicus (L-type) (SUZUKI, 1983).
The maximum amount of rotifer produced daily at a hatchery reaches several
billions. So, recently large tanks of 50 to 150 ton are usually used for the culture of
rotifers. The maximum culture density of rotifers is usually 150 -300 individuals/ml of Stype and 100 - 150 individuals/ml of L-type, respectively.
There are two methods for mass-culture of rotifers; the thinning method and the
subculture method. In the former method, rotifers are harvested according to the daily
increase, 10 to 25 % of all the rotifers everyday. After harvesting rotifers from the tanks
by filtering the water through a fine-meshed net, the same volume of sea-water
containing Chlorella in concentrations of 1 x 107 to 2 x 107 cells/ml is added to the tank.
Usually thinning harvests are carried out for 1 - 2 weeks, and then the whole crop is
harvested.
In the latter method, all the rotifers are harvested at the maximum density for
several days after the initial inoculation ( about 100 individuals/ml). And part of them is
used as seed to inoculate a new culture tank With this method, several tanks are used in
regular rotation. The method is of great advantage for the systematic production of
rotifers.
Marine Chlorella, baker's yeast and w-yeast are generally used as the feeds for
rotifer. Chlorella is the most excellent feed, but a large size tank is necessary for its
culture. If Chlorella is used as a sole feed for rotifer, the required total volume of the
culture tank will reach 1.5 to 2 times that of the tank for rotifer-culture. Although the
production of rotifer has increased remarkably in substituting Chlorella by yeast,
Chlorella is still necessary to stabilize the rotifer-culture, it is especially essential for the
initial feed, 1 to 2 days in a course of the culture.
The following agricultural fertilizers are usually added to the culture medium of
Chlorella : ammonium sulphate 100 g ; superphosphate of lime 10 - 20 g ; urea 10 g and
a chelating agent 5 - 10 g per ton of sea-water. But the latter can be omitted.
Results obtained by the HIROSHIMA Prefectural Fish Farming Center from April
to July 1982 give on example of a practical rotifer production. The Center used eight
outdoor 150 ton tanks (1 200 ton in total) for rotifer culture and twelve outdoor 200 ton
tanks (2 400 ton in total) for Chlorella culture. The period for the whole harvest after
inoculation was five days. Chlorella was used only at inoculation and the next day. On
the following days yeast alone was given. The crops were mixtures of L-type and S-type
rotifers and the former was dominant in May and June, the latter was in late June and
July. Total harvest was 1 200 x 109 (about 2.5 ton), the harvest per day was 19-2 x 109
individuals and they ensured the production of (6.3 x 106 sea-bream juveniles and 4 x
106 blue crabs, Portunus trituberculatus (FUSHIMI, 1982).
3.2. Culture of Tigrigpus japonicus
Although marine copepods is an important feed for the rearing of post-larval and
early juvenile red sea-bream, a complete technique for the mass-culture of them has not
yet been established. However, T. japonicus may be reared success-fully in large scale
operating tanks for two or three months in combination with rotifer. Using baker's yeast
as feed, the density of T. japonicus increases up to 20 to 30 individuals/ml within 3 to 4
weeks after inoculation. We can harvest about 2 kg of this species every-day for 50 days
from one 200 ton tank (FUKUSHO, 1978).
4. FURTHER PROBLEMS
Some problems still remain to be solved.
Firstly, it is necessary to systemize the process of fry production with automatic
operations in terms of mass-rearing of larvae and juveniles, and mass-culture of live
feed. For this purpose, live feed, especially rotifers, must be substituted by artificial feed.
Furthermore, it is important to clarify the cause and counterplan of heavy
mortality in larval and juvenile stage of red sea-bream.
CONTENTS
1.
2.
PARENT FISH AND EGG SUPPLY
1.1.
Parent fish
1.2.
Egg supply
LARVAL AND JUVENILE HEARING
2.1.
Outline of rearing
2.2.
Larval rearing in tanks
2.3.
Juvenile rearing in net cages
2.4.
Growth
2.5.
Survival rate
2.6.
Larval and juvenile feed
2.6.1. Sequential change of larval and juvenile feed
2.6.2. Daily feed consumption and feed supply
2.6.3. Dietary value of live organisms
3.
4.
2.7.
Disease
2.8.
Deformity
CULTURE OF LIVE FEEDS
3.1.
Culture of rotifer
3.2.
Culture of Tigriopus japonicus
FURTHER PROBLEMS
Fig. 1. Number of fry yearly produced at hatcheries in Japan. Numerals showing the
number of hatcheries which produced the fry of the species.
Fig. 2. Sites of national (•) and prefectural Fig. 3. Daily changes of number of eggs
spawned by red sea brem in outdoor 40
(o)
ton tanks , stocked with 20 females and
20 males (A), and 30 females and 31
males (B), respectively.
Fig. 5 Gowth and survival rate of reared red sea bream
Fig. 4. Relationship between body weight and the number of eggs spawned by a
female during a spawning season
Fig.6. Relationship between total length and satiated amount Fig. 7 Relationship between total length and satiated amount (Ts) or
(Rs) or daily feeding amount (Rd) of rotifer in larval red
daily feeding amount (Td) of Tigriopus japonicus in larval and
juvenile red sea bream
sea bream
Table 1
Certain fatty acids of total lipids from rotifer Brachionus pucatilis cultured with baker's
yeast.. Saccharomyces cereuislae. and marine Chlorella at Nagasaki perfectural
Institute of Fisheries during 1975 to 1977 (area %)
Fatty acid November 1975
May 1976
May 1977
Yeast Yeast + Chlorella Yeast Yeast + Chlorella Yeast Yeast
Chlorella
+Chlorella
Chlorella
Chlorella
16:0
6.1
4.2
14.4
7.1
13.2
19.4
8.7
11.7
16.8
16:1 ω7
27.2
26.7
20.4
26.5
22.6
22.4
24.2
16.6
24.3
18:0
3.8
4.4
2.2
4.3
3.6
1.9
4.8
6.0
1.7
18:1 ω9
26.8
25.8
10.1
29.1
21.5
11.0
33.9
22.8
10.1
18:2 ω6
8.9
5.1
4.7
6.9
6.3
3.4
5.8
10.4
3.2
18:3 ω3
0.6
0.6
0.1
0.2
0.5
0.2
0.6
2.2
0.4
20:1
3.6
3.4
1.7
4.2
4.1
2.3
6.0
3.3
2.4
20:3 ω3
2.0
2.3
4.1
0.9
3.0
4.2
0.4
2.3
4.4
20:4 ω6
20:4 ω3
0.4
0.6
0.2
0.4
0.4
tr
0.5
0.6
0.2
20:5 ω3
1.9
11.8
27.7
1.4
11.1
22.8
1.0
8.1
24.1
22:1
0.9
2.1
1.8
0.9
0.4
0.4
1.7
1.5
1.3
22:5 ω3
0.3
1.8
3.0
tr
2.9
3.4
0.2
1.7
3.8
22:6 ω3
0.5
0.5
tr
tr
tr
tr
0.5
0.9
0.5
∑w3
3.1
14.7
30.9
2.7
14.4
26.2
2.2
11.3
28.6
HUFA
Lipid %
1.4
2.8
3.7
1.7
2.2
4.2
2.3
2.3
3.8
Table 2. Effect of secondary culture with marine Chlorella on. the dietary value for red
sea bream larvae of rotifers cultured wlth baker's yeast and the change of fatty
acid distribution of total lipid in these rotifers (Kitajima et al., 1979; watanabe et
al., 1979)
Rotifer*
No. of fish
Total length at
the end of
feeding (mm)
Rate of
survival
Survival at (%)
activity test
Content of 20:5
ω 3 (%)
23000
23000
23000
23000
23000
23000
5.38±0.53
6.18±0.49
7.68±0.61
7.79±0.76
8.01±0. 54
8.76±0.55
20.2
58.7
71.7
75.1
65.4
79.8
9.2*o
54.3
67.8
60.7
94.3
99.6
3.2
8.7
27.0
24000
24000
24000
24000
24000
24000
24000
4.56±0.30
5.98±0.52
6.3l±0.54
5.03±0.45
5.76±0.39
7.03±0.81
7.15±0.52
22.1
49.5
50.9
50.8
49.5
60.4
58.1
45.6***
79.2
90.7
82.4
87.9
96.1
92.7
3.2
8.7
10.9
4.8
12.6
16.7
27.0
Experiment I
Y-rotifer
Y 10m C
Y 30m C
Y 60m C
Y 2h C
C-rotifer
Experiment II
Y-rotifer
Y 2h C
Y 6h C
Y 6h DC
Y 12h C
Y 24h C
C-rotifer
.* Y and C indicate the rotifers cultured with baker's yeast and those cultured with only marine Chlorella. respectively. The
abbreviations in the table, Y10mC, Y30mC, Y60mC, Y2hC, V6hC, Yl2hC and Y24hC, Indicate the Yeast-rotifers
cultured with marine Chlorella secondarily for 10, 30 and 60 min, and 2, 6, 12, and 24 h, respectively. V5hDC Indicates
the yeast-rotifers cultured with dried freshwater Chloralia for 6 h.
•• Survival rate during 24 h after fish were noved to the other aqualium at the end of the feeding experiment.
••• Survival rate during 24 h after 500 fish were dipt up out of water with a scoop net for 55 and moved to a 30 l tank
Table 3 Certain fatty acids of total lipids from baker's yeast, the yeast supplemented with
cuttle- fish liver oil (ω-yeast) and rotifers cultured with these yeasts
Fatty acid
16.0
16:1 ω7
18:0
18:1 ω9
18:2 ω6
18:3 ω3
20:1
20:3 ω3
20:4 ω6
20:5 ω3
22:5 ω3
22:6 ω3
∑ω 3 HUFA
Lipid %
Baker's yeast
ω -yeast
8.3-20.0
14.2-38.2
3.4- 8.4
26.1-13.9
2.8-15.1
0.5-6.4
tr - 1.6
13.4-16.9
5.0- 6.6
2.3-2.6
15.5-16.4
1.0-1.1
0.8-0.9
8.4- 9.2
3.0- 3.4
13.4 - 17.4
0.9- 1.4
12.8 - 15.6
33.5 - 35.8
12.3 - 15.6
1.0-1.6
Rotifers cultured
Baker's yeast
6- 7
26-27
3- 4
26-30
7- 9
3- 4
1- 2
1-2
0-0.4
ω - yeast
10 -12
10 -11
2-3
22-24
2-4
0.7-0.8
8 -10
3-4
9 -12
2–3
7-9
25 - 26
3.3 - 5.4
1.4-1.9
Table 4 Comparison of growth and survival rates of larval red sea bream fed on rotifers
cultured with respectively yeast or ω yeast.
Rotifer used
Expt. I
Expt. II
Expt.III
Expt. IV
ω -Yeast
Yeast
ω -Yeast
Chlorella
Y 12 h C
ω -Yeast
Chlorella
Y 3h C
ω -Yeast
Yeast
No. of fish
30 000
30 000
15 000
15 000
15 000
24 000
24 000
24 000
10 000
10 000
Total length
at end
(mm)
9.28±0.77
7.10±0.78
10.11±0.87
10.21±1.60
9.11±1.24
10.32±1.28
9.78±
8.85±1.09
10.91±0.94
6.24±0.62
Rate of
survival
(%)
73.5
13.0
76.2
57.1
27.9
76.9
70.1
27.6
68.9
3.2
Survival at activity test
(%)
86.0
12.5
92.9
91.7
93.2
92.5
91.5
55.8
95.5
45.9
Table 5 Certain fatty acids of total lipids in Artemia egg from three localities (Vatanabe et
al., 1982)
Fatty acid
14:0
15:0
16:1 ω 6
18:0
18:1 ω 9
18:2 ω 6
18:3 ω 3
18:4 ω 3
20:1
2O.4 ω 6
20:5 ω 3
22: 2
22: 6 ω 3
ω3 UFA
San Fracisco
A
B
3.6
1.3
25.9
14.9
12.9
5.5
3.7
3.5
19.8
20.0
2.5
6.3
4.8
22.4
0.6
0.8
1.1
0.3
0.6
0.6
0.9
2.7
0.3
0.6
0. 2
0.1
1.1
3.0
C
2.1
23.7
7.4
4.1
23.7
5.4
14.7
0.8
1.0
0.0
0.6
0.3
0 .1
1.2
Brazil
A
3.3
16.0
18.6
1.9
21.8
7.2
3.3
2.7
0.9
2.7
3.9
0.7
0. 4
4.4
B
3.4
18.2
14.4
2.9
23.7
6.4
1.1
3.2
1.2
3.2
3.5
1.0
0.8
4.1
c
2.1
13.7
13.8
3.2
28. 9
8.5
3.2
4.5
0.4
4.5
5.9
0.4
tr
6.3
Tien-tsin
A
B
3.0
2.8
12.1
12.7
22.6
24.0
3.5
2.9
25.2
20.2
4.1
3.8
5.5
6.0
0.9
1.0
0.2
0.4
1.2
1.1
9.2
10.2
9.2
10.2
C
2.0
12.7
22. 4
3.3
28.3
4.4
5.1
0.7
1.5
11.3
11.3
Fig. 8. The direct method for improving the dietary value of living feeds.
Fig. 9. Incorporation of lipids emulsified with various kinds of reagents (A, B, C and D' in
rotifers by the direct method. Reproduced with permission from Bull. Jpn. Soc. Sci Fish.,
Watanabe et al., 1983.
Fig. 10 Skeletal curving point in lordotic
deformity of red sea bream
Fig. 12
Relationshp between uninflated swim.
bladder and Iordotic deformity In 20 rearing
groups of young red sea bream of about 50
mm TL.
Table 6
Yearly occurence of deformities in red sea bream produced at the Aquaculture Research
Laboratory of Nagasaki Prefectural Institution of Fisheries
Year
No. of fry produced ×103
Date of examinations
No. of fish examined
Total length mm
Curving
angle
<10
Lordosis % <20
<30
30>
Total
Short statue (fused
centrums)
Other deformities
Total
1974
420
12 Aug
1975
270
1 Sept
1976
490
26 Jul30 Aug
1024
64.9112.3
497
93.3
152
118
3.4
20.5
9.3
8.2
41.4
2.8
4.6
13.2
7.9
3.3
28.9
2.0
4.5
8.3
2.3
1.9
17.0
5.7
5.0
49.2
5.9
36.8
6.5
29.0
Fig. 11
Changes in percentage of individuals with inflated swim bladder and lordotic
deformity of marked red sea bream.
± : 100 > in skeletal curve
+ : 100 < 200
+ + : 200 < 300
+ + + : 300 < 400
Fig. 13
Change in angle of skeletal curve in lordotic individuals by repeated observations
of particular ones. Solid line showing the period with depressed swim bladder,
and dotted line the period with normally inflated swim bladder. A: group of slightly
lordotic individ., B: group of seriously lordotic Individ.
Table 7. Comparison of incidence of swim bladder inflation in the larval red sea bream
reared in the tank scaled with a layer of liquid paraffin and the open tank (Exp. I)
Date
(Days after
hatching)
May 6( 8)
8(10)
10(12)
N
9
28
30
Sealed tank
Incidence
TL ± SD)
(%)
(mm)
3.61±0.17
0
3.95±0.14
0
4.12±0.21
0
N
9
23
30
Open tank
TL
(mm)
3.61±0.17
3.98±0.22
4.29±0.27
Incidence
(%)
0
41.7
73.3
Table 8 Comparison of incidence of swim bladder inflation in the larva! red sea bream
reared in the tanks sealed with a layer of liquid paraffin and the open tank (Exp, II)
Date
Sealed tanks
(Days after
Non aeration (A)
Aeration (B)
hatching) N
TL
Incidence N
TL
Incidence
(mm)
(%)
(mm)
(%)
May 15 ( 8) 11 3.70±0.20 0
23 3.92±0.40
0
17 (10) 28 3.91±0.32 0
2S 4.37±0.24
0
19 (12) 25 3.93±0.26 0
29 4.74±0.44
0
21 (14)
30 5.33±.0.51
0
23 (16)
30 5.75±0.48
0
25 (18)
30 6.11±0.43
0
29 (22)
30 7.38±0.53
0
Open tank (C)
N
TL
(mm)
Incidence
(%)
26
23
27
29
30
30
25
3.82±0.26
4.11±0.25
4.62±0.55
5.21±0.46
5.49±0.50
6.30±0.56
7.52±0.S9
53.3
76.7
65.5
70.0
31.8
90.0
92.0
Table 9 Comparison of incidence of swim bladder inflation in the larval red sea bream
reared in the tank blown at the water surface with an electric fan and in the nonblown tank (Exp. III)
Date
(Days after
hatching)
Jun. 9 ( 4)
11 ( 6)
13 ( 8)
16 (11)
20 (15)
27 (22)
Jul. 1 (26)
N
18
30
23
30
30
30
30
Blown tank
TL
(mm)
3.28±0.12
3.63±0.18
4.06±0.18
5.08±0.37
6.84±0.54
11.37±1.50
17.34±1.93
Incidence
(%)
0
3.3
0
0
6.7
13. 3
10.0
N
22
30
29
2S
30
30
32
Non-blown tank
TL
Incidence
(mm)
(%)
3.28±0.14
9.1
3.70±0.20
46.7
4.08±0.27
69. 0
5.24±0.45
60.7
6 62 ±0.60
66.7
11 .92±1.09
73.3
17.59±1.83
84.4
Fig. 14 Comparison of swim bladder inflation among the groups of larval red sea bream
transferred to the tanks with open surface, after rearing in the tank sealed with a
layer of liquid paraffin for various duration, 2 to 16 days, after hatching (A-F).
Numericals in each graph denotes days after hatching, among which the top one
shows the day when the larvae were transferred from the sealed tank to each
tank with open surface. Shadow area; individuals with uninfiated swim bladder,
open area; individuals with inflated swim bladder
Fig. 15 Comparison of incidence of swim bladder inflation and the lordotic deformity in
the larval red sea bream reared in the tank scaled with a layer of liquid paraflin
(P) and the open tank (C).
The mark of shows mean ± SD (n=30). The degrees of lordosis are
expressed by the Supplementary angle at the curving point : ± less than 100 ; +,
100 to 200; #, 200 to 300; #. 300 to 400
Fig. 16.
Comparison of specific gravities in the young red sea bream with inflated
swim bladder and uninflated one
Fig. 17.
Comparison of incidence of swim bladder in the larval, red sea bream fed on
Chlorella-rotifer (A), ω -yeast-rotifer (B) and Y3C-rotifer (C), reapectively.
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FOUR MARINE SPAWNERS IN EUROPEAN HATCHERIES
Ms. N. DEVAUCHELLE
INTRODUCTION
The idea itself of developing commercial hatcheries for marine fish in Europe is
recent (GIRIN, 1980), But it has now been established, save exceptions, that for seabass gilthead sea-bream, sole and turbot, development depends on having under control
the production of eggs. Thus it is important for the aquaculturist to know the answers to
the questions, where, how, how long and for what results must one, as soon as a
hatchery has been created, envisage the construction of a unit for spawners.
From the beginning of the Century, specialists in rearing have remarked that the
turbot (ANTHONY, 1910 ; BUCKLAND in MALARD, 1899) and the sole (BUTLER, 1895)
could reproduce in captivity. But the reproductibility of the phenomenon has still to be
demonstrated. For this, around the years 1960 - 1970, most of the works were aimed at
obtaining, as quickly as possible, fish caught at sea, to spawn. Then hormonal induction
was commonly employed for maturation followed by spawning and manual fecundations
(BARNABE, 1976 a ; BRASOLA, 1974 ; FLUICHTER, 1972). On parallel, the IFREMER
Center in BREST concentrated on the possibilities of fish reproduction in captivity, in
conditions similar to those found in natural environments. At first, all manipulation was
avoided (GIRIN 1979). Later on, so as to simplify the management of the broodstocks
and to optimize that of hatcheries, operations were developed, such as the alteration of
the seasonal productions of eggs, the use of spawners born in hatcheries, the
modification of food diets and artificial spawnings.
Today, all the results obtained permit a comparison to be mode between the
many techniques employed to obtain eggs.
1. GENERALITIES
1.1. Stock constituting (Tables 1 - 2 - 3)
The first operation to carry out when a hatchery has been created, is to obtain
good size spawners from the sea. This is what we have done so as to constitute the first
stocks. But little by tittle, long term management proved more efficient. The principles to
employ are as following : acquisition of 3 to 5 age groups of each species, within the
limits as shown in table 1 ; substitution, every 1 to 2 years, of the older age groups by
younger ones. Their number is calculated from specific productivities (Table 6) and the
latency period, usually observed between their capture at sea and their first spawning in
captivity is taken into account ; this being, one year for sea-bass, 1 to 2 years for
gilthead sea-bream and 2 years for sole and turbot. Sea-bass and gilthead sea-bream
are transported in tanks of 1,5 to 2 m3 , by road. Loads never exceed 100 kg/m3 . For
distances requiring, at maximum 4 hours, it is not necessary to oxygenate the water. For
the same length of time of transport, flat fish are placed into plastic bags with oxygen, at
a rate of 1 volume of fish for Two volumes of water. When the journey is less than 2
hours, turbot are transported without harm, in open plastic-bags without water.
When fished, the animals are sorted out according to their sex (DEVAUCHELLE, 1984) so as to adjust the choice of fish to the real needs of the station. The
males are immediately marked and separated from females. Immediately, on their arrival
at the reproduction stations, they are treated with green malachite formol so as to avoid
the eventual propagation of parasites to the native stock (Table 3). If the animals should
show wounds, they are treated with antibiotics. The lowering of the salinity to 20 ‰ for 2-
3 days, also permits the rapid recovery of weak sea-bream. Nevertheless, strict vigilence
is from then onwards, the rule to abide by : indeed, the first signs of weakness or
parasitosis require quick curative treatments. As well as the treatments shown in Table
2, it is henceforth recommended to give intraperitoneal injections of vitamin C to male
turbot.
The doses employed are 100 mg/kg of fish every 15 to 30 days until complete
recovery has been obtained (MESSAGER, pers. comm., 1985). Generally, the
Frequence of treatments is increased when manipulations are performed and when
there are important thermic variations of the sea-water.
The week following their transfer, the healthy fish are marked (Table 3); the
others are marked after a Few weeks of acclimatization to captivity. The idea! marking
for the breeders is that which permits to individually identify, in situ, the fish according to
their sex and age group. For turbot, the technique employed is a branding iron which has
been cooled in liquid nitrogen. The operation takes 8 to 12 seconds and must be
reperformed, according to the growth speed of the fish, every 6 to 12 months. For the
sea-bass and gilthead sea-bream, this method is not sufficient. Also, the labelled brands
proposed on the market have been dropped. They are too small and also cause wounds
and necrosis. The magnetic brand, less traumatic, is still costly and does not permit to
distinguish the animals in the tank. In the particular case of spawners, it has thus been
confirmed as inefficient.
Therefore up to the present moment, sea-bass and gilthead sea-bream are
identified by simply injecting Indian ink into the bottom of the pectoral fins (SUQUET,
1986). The absence of individual marking then calls for, before any hormonal induction
for maturation can take place, the control of the state of advancement of the
gametogenesis by means of a catheter (BEDIER, 1979) or by performing a biopsy
(DEVAUCHELLE, 1984).
The fish (sea-bass, gilthead sea-bream, turbot and sole) sorted out and marked
according to their sex, are placed into the tanks for 4 to 6 years, the characteristics of
which can been seen in Table 2. But, sometimes, there is not enough space. Certain
batches whose spawning season has not been altered are then kept in cages when it is
not their period for spawning. This practice, rarely employed, refers to turbot which, in
appearance, seem less fragile than the other three species. In all cases, the adaptation
of the fish to captivity is facilitated by the presence in the new stock of some "Veterans"
who incite the others to take inert food while at the same time reducing the fasting period
Which normally follows, when fish are captured (15 to 45 days depending on the
season).
1 . 2. The storing tanks
They contain 5 to 40 m3 of sea-water. The depth of the water varies from 0.7 to
1.7 m. The materials employed for the construction of the tanks are not standardized. If
circular, of subsquare or rectangular section, in polyester, cement, treated wood with
PVC covering, it is important, for the flat fish caught at sea that the ranks he lined with
drained sand (DEVAUCHELLE, 1980). In this case, the upkeep charges increase. The
sand must be, in fact, purified regularly by means of a drain or by chemical treatment
(formol 38 %, 1 000 ppm) so as to avoid the development of parasites with resistant
spores. In summer, the tanks are covered individually which limits the development of
algae. The average light intensity at the surface is 1 500 to 2 000 lux.
The water distributed to the tanks by means of PVC pipes, is not recycled.
Filtration (*a) is necessary with the use of thermic exchangers, (*b) but when there is no
regulation available unfiltered water may be used.
*a = LACRON Filters
*b = Exchangers with titanium plates
With the exception of temperature, the characteristics of the sea-water produce
natural variations in our region (Table 4). The oxygen saturation rate is however liable to
vary within the alarm limits (50-130 %) depending on the rates of renewal and the
induced temperature changes of the water especially.
Regular controls are necessary. The dissolved nitrogen gas tenor can also be
surprising, and create perturbations : filtration of air at pump level, turbulences in the
pipes and the heating of the water are factors which can bring about the abrupt increase
of dissolved gas tenors. This is remarked; depending on the species, by the apparition of
exophthalmia (sea-bass) or gassy bubbles which accumulate under the skin or at the
extremities of the fins (sole, gilthead sea-bream). In general, intense bubbling in the
tanks will avoid the incidental mortalities and favour the rapid resorption (in around 24
hours) of the gas bubbles. The phenomenon is more insidious in sand bottom tanks : the
air lift which, ensures the drainage also creates air pockets. In burying themselves, the
fish (sole) then die quickly of gassy embolism.
Normally, the characteristics of the sea-water are controlled each day by means
of 3 classical devices ; the thermograph, the refractometer and the oxyimeter.
1.3. The food
The food is distributed ad libitum 2 or 3 times per week, in a fresh or frozen form
(loss than 3 months of conservation). Except in particular tests (cf § 2.5), no vitamins are
added. The quantities distributed vary according to the seasonal temperatures and the
gametogenesis. They are situated between 4 and 24 % of the daily averages (fresh
weight of the food/fresh weight of the spawner x 100). The quality of the food depends
on local fishing. But more often, fat and lean fish are distributed alternatively, to turbot,
sea-bass and gilthead sea-bream. Also, depending on the supply stock possibilities,
mussels, clams or crabs are given to sea-bass and gilthead sea-bream.
Sole have a different food diet: : molluscs (Challysta chione, Glycimeris
glycimeris, Laevicardium crassum ) et polychaeta (Nereis diversicolor et Nephtys
hombergii).
1.4. Spawning techniques
In captivity, the four species can reproduce, without human intervention, naturally
fecundated eggs. But in certain circumstances, artificial spawning techniques are
employed. This involves spawning by hormonal induction of sea-bass and gilthead seabream. HCG (200 - 500 U.I./kg O) and LHRH ( 1 u g/kg) are then used by following the
indications by SUQUET (1986). These hormones synchronize the female ovulations and
can be considered as a technique to employ for short period alteration. It is effective only
with advanced vitellogenesis :-ovocytes of 650 u or more, for Mediterranean sea-bass
(SUQUET, 1986) - Whatever, the quantity of hormones employed, the injections are
then followed by spawnings and natural fecundations.
Artificial spawning for turbot consists of "stripping" operations and of dry or wet
artificial fecundations without the use of hormones (BARTON, 1981).
The sole neither reponds well to spawning by hormonal induction nor to
abdominal pressures.
Also, artificial fecundation, without the need of killing the male, is difficult to
envisage due to the size of the testicules (RGS maximum 0.2 % - DENIEL, 1981). with
this species, artificial reproduction is not usually employed.
Artificial spawning techniques alone are employed in some hatcheries. But as
they are not standardized, important differences are obtained in the interpretation of the
results. To understand more clearly the possibilities of reproduction in captivity, we have
willingly left aside the principal objectives of research. The comparison of natural and
artificial spawning will thus depend on the data obtained outside the IFREMER Centre in
BREST.
1 5. Collection and Treatment of eggs
Systematic measures : Each batch of eggs (or spawnings) collected at the outlet
of the tank or after artificial spawnings, are subjected systematically to aliquot measures,
for diameter and viability rates. The hatching and bone malformation rates of the larvae
with swim bladders are estimated after the standard incubations have been performed in
volumes of 0.1 liter (DEVAUCHELLE, 1980),
Particular measures : On the other hand, the weight of the eggs has been
estimated for 13 spawnings of sole, 17 spawnings of sea-bass and 48 spawnings of
turbot, involving a large range of egg diameter (DEVAUCHELLE, CLADAS, 1983 ;
DEVAUCHELLE, in press).
The optimal conditions of temperature and of salinity for hatching, along with the
duration for incubation have also been established in an experimental incubation unit
under strict control (DEVAUCHELLE et al., in press). On the other hand, measures of
the biochemical composition on the eggs have been carried out between 1979 and 1982
(DEVAUCHELLE et al., 1982).
On parallel with these tests, routine incubations are carried out in incubators of
25 to 40 liters (DEVAUCHELLE, 1983). The mobile incubator is operated by the rotation
of an electric motor having a frequence of 1 rotation/minute.
Whatever the volume be in the incubator, the embryogenesis takes place in
natural photoperiod conditions. The temperature can be regulated as desired, between 7
and 250 C. The water is filtered but no chemical treatment is performed. Loads do not
exceed 7 g of eggs per liter which is 5 000 to 10 000 eggs per liter depending on the
species. These values have been defined as optimal superior limits for quality hatching.
1.6. Principle of the reproduction/incubation facilities (Fig. 1)
The facilities are separated from those for larvae rearing, on account of the
following reasons : the volumes and quality of the water required by these two stages
are very different from the others. On the other hand, incubation in small volumes
permits, if necessary, to individualize the incubation, to control more adequatly the
abnormal mortality of eggs and the consequent development of diseases. Also the
estimation of malformations and the hatching rates are facilitated, thus enabling a better
interpretation of the results for larvae rearing.
2. RESULTS
2.1. Maturation - Natural spawning and fecundation with neither control of the
temperature nor photoperiod
2.1.1. Spawners
The annual mortality rate (Table 2) recorded, is feeble for sea-bass and gilthead
sea-bream : 2 - 5 %. It is around 5 and 10 % for sole and turbot. But although sporadic,
the losses with the turbot can be spectacular and destroy more than 50 % of the stock.
This happened twice in 10 years, at periods ,when there were sudden rises in
temperature. The origin of these mortalities has not yet been defined but they are
connected with those provoked by bacterial diseases such as vibriosis (LIEWES, 1984).
Both males and females, at advanced mature stage, are the most affected. For the
present, it has been remarked that simple intraperitoneal injections of vitamin C at rates
of : 100 mg/kg of fish reduce these mortalities.
The growth of the wild spawners in captivity seems on general, superior to that
remarked at sea (figure 2), with however the exception of the gilthead sea-bream. There
are two explanations for this. The data of reference for wild gild-head sea-bream
concerns the Golfe du Lion, where the average annual temperatures are superior to
those found in the Brittany region. On the other hand, captivity, by interfering with the
Winter migrations, permits the gilthead sea-bream to sustain lower temperatures than it
could normally, at sea.
2.1.2. The tank volumes
We haven't remarked a clear difference in the productions of eggs in 10-12 m3
and in 40 m3 , with maximum loads of 7 kg/m3 for sea-bass, turbot and gilt-head seabream. On the other hand, the results obtained for sole are comparable, in 5 and 17 m3.
Smaller volumes have not been tested, although FONDS (1979) remarked natural
fecundations of sole in tanks of 1 500 liters. However, at experimental level and a fortiori,
egg production tanks, no smaller than 5 m3 are, as far as we are concerned, the lowest
possible limit advisable : In smaller tanks, the results obtained from a very small amount
of fish, should not be of statistic signification.
Finally,the experiment proves that groups of tanks of 10 to 15 m3 , with shallow
water (0.7 - 1 m) are more suitable for hatcheries whose principal aim is profitability : the
state of the population can, in this way, be easily controlled. Also, the upkeep of the
tanks, the manipulations and egg retrievals are more easily performed.
2.1.3. The gametogenesis of females and the spawning season (Table 5)
The recent use of biopsies performed on market fish has permitted to define
when the gametogenesis begins with the different species : In September/ October,
which is 3 to 5 months before sea-bass and gilthead sea-bream begin their spawning
period; in January which is 4 to 6 months before turbot begin to spawn. For sole, the
sexual rest period has not been clearly defined. As at sea, the gonads of sole contain
several generations of ovocytes all year long (LAHAYE, 1972). For the other three
species, the time lapse between the first growth of the ovocytes and the beginning of the
spawning is still not precise, as this depends especially on the seasonal thermic rates.
The temperature indeed, has an effect on the speed of the vitellogenesis and
acts as a minimum/maximum threshold for the oviposition. It has such an effect, that it
can reduce by around 25 % , the duration time for the gametogenesis of each of the
species concerned, totally suspend the spawning season or advance or delay its date :
with the sea-bass for example, the gonads contain, from the beginning of December,
ovocytes, the diameter of which (800 to 1 000 um) predicts future ovulation, as is
remarked in the Mediterranean. While at this period, the temperatures of the sea-water
(7 - 8 °C) are at the lowest limits for spawning. Although there exists an advanced
ovogenesis, we must wait until Spring when the water is at 9 - 10° C or more, to collect
the first sea-bass spawnings. It is evident that the latency period can differ from year to
year. Consequently the apparent duration for maturation will also vary. However, as the
threshold temperatures for the gametogenesis and spawning are known (Table 5) we
can, by means of thermoregulation, be prepared for the effects of seasonal conditions
which can be exceptionally unfavourable.
On the contrary, if necessary, the variations in temperature permit blocking the
production of eggs, at certain periods. For delicate fish, such as the gilthead sea-bream,
this ensures a synchronization of the spawnings, without the needs of manipulations nor
hormone injections. With this species, the variations of 2 to 5° C in 24 hours are well
tolerated and now practised in certain Centres for the production of juveniles. But more
often, when there exists neither thermic nor photoperiod controls, spawning will begin a
little later in tanks than at sea : end of February/beginning of march for sole and seabass, end of April to the end of June for turbot. Gilthead sea-bream spawn in Winter time
if the temperature of the water reaches more than 13° C, but this has never happened
naturally in the Brittany region in tanks having a non thermoregula n of the surface water
supply. The spawning seasons continue until May (sole), June (sea-bass) and August
(turbot). On the other hand, the sexual rest periods, solely associated with the presence
of ovogonies founds in the gonads, lasts at the most for two months : in Summer, for the
sea-bass and gilthead sea-bream, at the end of November/December for the turbot.
Finally, it has been remarked, that males at least, produce sperm throughout the
whole spawning season, from November to August, for the sea-bass, from December to
October, for the turbot.
2.1.4. Fecundity and quality of the eggs (Table 6)
In non limiting conditions of temperature and photoperiod, the relative fecundity
(*a) is inferior by 20 to 50 %, throughout the first two spawning years, for fish at the
beginning of their reproduction activity. The adults caught at sea do not recover a normal
level of fecundity until the second cycle of spawning takes place in captivity. The
fecundity is then stabilized as shown in table 6. We then remark that our data
corresponds quite definetely to fecundities estimated for mature sea-bass (table 6). They
are however 2 to 3 times inferior for turbot, sole and gilthead sea-bream.
*a = Number of eggs collected per kg of female
Fish spawn from one to twelve times depending on the species. The eggs of the
female sea-bass are all set free at a few days of interval. The spawning period lasts
longer for the gilthead sea-bream, sole and turbot : a female turbot con for example
produce eggs for 7 to 8 weeks, every 3 - 5 days.
The viability rates are different with round fish than with flat fish. They are very
high for gilthead sea-bream and sea-bass as only 10 to 20 % of the spawnings have a
viability rate of less than 70 %, more often remarked at the beginning and end of the
season. For sole, although the viability rate of the eggs is on average less than 10 %
than that obtained with sea-bass and gilthead sea-bream, results can vary from year to
year.
With a 33 % viability rate, the turbot is the most complex species. This figure has
been obtained on averages estimated over several years. But the detailed study of the
results shows important variations of the annual average rates 0 to 81 %. In bad
seasons, the cause is the absence of fecundation rather than the quality of the ovules.
Neither the adaptation of tank volumes (GIRIN, 1979) nor the necessity of sand bottoms
(DEVAUCHELLE, 1980) permit the explanation of this phenomenon. In fact, once again
certain physical parameters of the sea-water seem to perturb the process of fecundation.
2.1.5. The eggs : Description and incubation (Table 7)
The impregnated egg is a pelagic sphere which, in an incubation environment, is
slightly deformed into the shape of a rugby ball. The different species differ in diameter,
weight, and aspect of the lipidic reserves (Photos ). When mature, the egg of the seabass contains 1 to 5 lipidic drops which represent 2 to 3 % of the total volume. The egg
of the sole contains a multitude of diffused lipidic drops. The eggs of gilthead sea-bream
and turbot contain one globule with slight variations in daimeter : 180 to 210 um (turbot),
210 to 240 um (gilthead sea-bream). The analysis of the eggs of sea-bass, sole and
turbot (Table 12) indicates the water, lipid, protein and ash tenors.
After the fecundation has taken place, the egg hydrates. The rate of humidity
increases by 25 % about. The perivitelline space appears 15 to 60 minutes after the
emission of the ovule, independantly of the fecundation. The diameters vary from one
batch to another : 6 % for sea-bass and gilthead sea-bream and 10 % for sole and
turbot. Within these limits, there is no clear correlation between the diameter and the
viability rate or bone malformations (DEVAUCHELLE, 1980). However, the dry weight of
the egg increases according to the diameter (Figure 3). The duration for incubation
depends on the temperature of the sea-water and on the species involved (Figure 4). As
an indication, for turbot, the four major phases Morula, Gastrula, Neurula and
prehatching represent on average 17, 15, 52 and 10 % of the total duration of
embryogenesis. The risks of mortality are reduced when the incubation lasts 3 to 6 days
(Table 8), which means at near optimal temperatures defined for spawning.
At the IFREMER/Centre in BREST, the salinity had been subjected to precise
experimental tests for turbot and sole. This paragraph deals exclusively thus with these
two species. It is important to know at first that salinity has no effect on the duration of
incubation but determines, in synergy with the temperature, the hatching and larvae
malformation rates. The effect is more pronounced at stages considered as fragile :
(Figure 5). However, in all cases, more than 70 % of the viable eggs hatch without
malformation at between 25 and 35 ‰, more than 50 % up to 15 ‰. The sole can
support better than the turbot low temperatures and salinities. When the eggs tested are
at Gastrula and Neurula stages, considered to be more resistant than the Morula stage,
the quality of the hatchings is equal to 15 and 35 %. But, In all the cases, 10 % is the
limit not to be exceeded for both turbot and sole. In extreme conditions of incubation, the
individual characteristics of the different batches of eggs are expressed by the level of
the mortality rate ; in optimal conditions, the differences are more remarkable at larvae
malformation level.
On general, eggs are fragile at Morula and prehatching stages. With turbot,
especially, all stress of mechanical or thermic origin must be avoided during the first and
last fifth of incubation. It must be remarked finally that the larvae with air bladders, resist
better than the egg at Neurula stage, the variations in temperature and mechanical
shocks. The larvae are, in consequence, propice for transport, although at this stage of
development, they seem to be more sensitive to chemical treatments, especially chlorine
(DEVAUCHELLE, 1980).
The experimental tests, carried out in automatic incubators of 1 liter (Table 6), in
optimal temperatures and salinity, lead us to the following conclusions : The hatching
rate of viable sea-bass and gilthead sea-bream eggs was 10 % greater than those of
turbot and sole. The average rate of malformations was low : 5 %. In these conditions,
the differences in results between the batches of eggs of the same species reflects the
way in which the rearing was carried out prior to incubation : spawning conditions or
genetic factor. Employing the same treatment, 00 % for the hatching rate and 30 % for
the malformation rate of sole and turbot eggs have been obtained. For the sea-bass,
they are respectfully 20 and 14 % on average. Generally, delayed hatchings are
associated with high rates of malformation.
Eggs end larvae which have just been hatched or are about to.
A : Sea-bass - B : Gilthead sea-bream - C : Sole - D : Turbot
The biggest incubators (25 - 40 liters) allow on average a hatching rate of 60 to
70 % and rates of malformation of 5 to 15 %. The differences between the species are
less pronounced, as the results reflect essentially the general conditions of incubation,
especially mechanical shocks. Other incubation techniques are employed with these
species. But in all cases, their effect fulness depends especially on having the same
standards : water, incubation densities, temperature levels, salinity and mechanical
shocks (DEVAUCHELLE, 1980).
In the actual state of affairs, incubation is not a limiting factor for rearing. The
selection of the spawnings depends essentially on the management of the larvae
rearings. We could however schedule the sorting out of egg batches according to when
they resist less to shocks of thermic or saline origin, at the beginning or end of
embryogenesis. The selection can also be obtained by staggering the hatchings.
It can be finally concluded that a big hatchery can reasonably envisage the use
of 50 % of the viable eggs collected, by rationalizing the incubation techniques, which
represents for 1 kg of females : 100 000 larvae of sea-bass, 400 000 larvae of gilthead
sea-bream, 50 000 larvae of sole, 25 to 60 000 larvae of turbot.
2.2. Artificial spawning (Table 6)
In our regions, artificial spawnings are not up to standard for sole. They are often
not necessary for gilthead sea-bream which spawn daily a great quantity of eggs, during
many months. It is, on the contrary, employed for sea-bass so as to synchronize the
spawnings of several females and for turbot so as to compensate for irregular
fecundations.
With sea-bass and gilthead sea-bream, hormonal inductions for spawning rises
the mortality races of spawners by about: 10 %. On the other hand, it seems to decrease
the requirements of the sea-bass concerning environment.
Indeed, the volume of the spawning/fecundation tanks can be reduced to 4 - 5 m3
without causing any disadvantage, while 10 m3 seems to be the minimum volume
compatible with natural maturation-spawning-fecundation (BARNABE, 1976 b). The
actual progress made in the hormonal induction of spawning guarantees relative
fecundities and high rates of viability for both these species. The differences when
compared with natural spawnings are all the less evident as the majority of hatcheries
carried out alternatively both techniques. It must also be remarked that LHRH is greatly
employed which on the contrary to human gonadotropine avoids antigenic reactions
(BARNABE, 1985).
With turbot, the stripping, less selective than the natural oviposition, doubles the
relative fecundity. Nevertheless, the average viability rates are very low. They recall to
mind the first artificial fecundations carried out on sea-bass. Indeed, each female turbot
has its own rhythm for ovulation (Mc EVOY, 1985) and six hours afterwards, the
fecundation levels decrease. Due to the working hours, the hatchery often neglects this
rhythm : the difference in the quality of the eggs is evidently remarked. for the moment,
the females are rarely selected on account of their rhythm of ovulation. On the other
hand, there is still no effective means of synchronizing the spawnings. When fecundation
does not take place naturally, the aquaculturist must therefore found his profitability
calculations on the maximum figure of 33 % for the viability rates. On the other hand,
abdominal pressures, properly carried out do not cause mortality.
2.3. Alterations in the seasonal spawnings
2.3.1. Method
In temperate regions, the process of gametogenesis depends essentially, as
already stated, on the temperature and photoperiod, when the salinity rate is at around
30 and 40 ‰. The first alteration in spawnings were thus, naturally based on the
simulation of thermic and photoperiod cycles found in our region. The spawnings were
either brought forward (GIRIN and DEVAUCHELLE, 1978) or delayed (DEVAUCHELLE,
1983) in report to normal cycles. Later on, we continued little by little, to get as near as
possible to the optimal light and temperature conditions remarked at normal spawning
season (Table 5). This approach, along with chance (abrupt variation in temperatures)
led us to simplify progressively the technique for alteration.
Two objectives were focused:
1) To reduce to maximum the heating and cooling costs of the sea-water while
maintaining a high quality of the eggs.
2) To know the respective effect of both the temperature and photoperiod
factors on the gametogenesis and the spawning processes.
Some results, which were obtained through an experimental approach, have
been reproduced over 2 or 3 spawning seasons for each species. On parallel,
comparative tests have be conducted on the turbot (DEVAUCHELLE, in process).
2.3.2. Results
The mortality of spawners is comparable to that registered for those which have
had no alteration carried out on spawning. On the other hand, only alterations of more
than 1.5-2 months is taken into account here. Below these values, this is a short term
alteration which calls for only simple thermic regulations (cf § 2.1.3.).
Generalities : The schematization of the ideal techniques for spawning would lead to
excluding numerous possibilities which have not yet been tested. In temperate zones,
the results can be resumed as follows : as remarked in normal spawning periods, the
light conditions define the beginning of the gametogenesis (previtellogenesis phase).
This action is really evident with the turbot. By this fact, it is now common to alter the
spawnings according to the photoperiod variation alone. The level of temperature is
controlled when necessary, depending on the rearing zone. The spawning for the four
species taken into account here, can be altered, at any time of the year by following the
indications given in table 9, which are very close to the optimal conditions remarked in
natural spawning seasons.
When alteration begins : The groups of fish whose spawning is to be altered for the first
time must preferably take place at the end of their sexual rest period. The weight
progression must be above all normal, which is, according to the bibliographical data,
from + 2 to + 20 % depending on the species and age, (Figure 2) in report: to the end of
the preceding sexual rest. The alterations begin normally with the contraction of the
photoperiod cycles and therefore an acceleration of the gametogenesis or with a long
continuous light period (turbot). Delayed spawning of more than 1.5 months are less
frequent, but possible, by blocking the photoperiod cycle during the sexual rest period.
In any case, the duration of the gametogenesis can be brought to the minimum
time length remarked in natural environments, which is 3 - 4 months depending on the
temperature. Taking into account the minimum duration of sexual rest (2 months) and
average duration of the spawning seasons, it is possible to provoke the oviposition every
7 months (Table 10), but the decrease in the fecundity and of the quality of the eggs
(Table 11) following the more reasonable contractions of the cycles (10 months instead
of 12) lead us to consider this forcing as a last resource. The medium results obtained
for the second oviposition of sea-bass confirms this more so (SUQUET, 1986).
Ideally, once the alteration is obtained, the advanced or delayed photoperiods
must be stabilized at 12 months. The control of the temperature will remain
circumstancial, within the limits indicated further above. By this fact, the beginning and
end of spawning escapes the seasonal changes in the temperature and the sea-water,
more so than in natural conditions. Naturally, the seasons reach their maximum : 5 - 6
months for gilthead sea-bream, 3-4 months for sea-bass and turbot, 3 months for sole.
On the other hand, the influence of the alteration is not directly remarked, as to
concern the diameter of the eggs. Even if the eggs spawned outside the normal season
are. often smaller, it appears more advisable to correlate these variations to the thermic
rates (cf Discussion).
The alteration can finally be accompanied by modifications of the global
composition of the eggs. The first analysis on sea-bass, turbot and sole, showed
increases in the total lipid rates and reductions in the protein rates when compared with
wild fish and fish eggs in capativity whose spawning had not be altered (Table 12). The
reports of the lipid categories also differ, while the unsaturated fatty acid rates contrast
with spawning obtained in captivity and ovules of fish, caught at sea.
In this case, the temperature, on average higher, provoked more regular feeding
habits with spawners. Therefore, it can be assumed that the alteration has an indirect
action. Taking into account the implications which it can have on the survival of larvae, it
must nevertheless be considered. With the improvement of the larvae rearing
techniques, especially those for sea-bass (COVES, 1985), there exists ways of verifying
the effects of the different quality of eggs for the survival of larvae and juveniles.
2.4. The origin of the spawners
2. 4. 1. Methods
As there is no data available on the genetic selection, the marine fish spawners
born in hatcheries, are often chosen first. To avoid important sex-ratio unbalances,
sorting out according to their sex is thus necessary, before they are finally placed into
the reproduction unit. Unfortunatly, the sorting out and production of spawners born in
hatcheries has only been recently adopted. In Brittany, only data on the growth of sole
and turbot is available. On the other hand, a test of comparison was carried out on turbot
so as to evaluate the differences in fecundity between fish from hatcheries and those
from the "wild". On parallel, a test on feeding was also carried out (Table 13).
2. 4. 2. Results
Sole and turbot from hatcheries have a rapid growth phase at high temperatures.
But, as soon as they are placed into natural conditions of temperature, their growth rate
slows down when compared the that of wild fish, or at least remains the same as the
latter (Figure 2). When the first cycle of maturation takes place, they are inferior in
weight to wild fish of the same physiological age. Also, in both cases, males become
mature a year before females do.
As for the follow up of the fecundity of turbot, it should be noted that, during the
test, abnormal mortalities were remarked. They were reduced by intraperitoneal
injections of vitamin C (100 mg/kg of fish). In these conditions, the number of eggs
spawned by the fish in hatcheries is 36 % less and weight losses following spawning is
at 3.3 % against 5.7 % for wild fish.
It must be recalled that the fecundity level is a result of the influence of a great
number of parameters which have marked the history, even of long) ago, of the spawner
(STEARNS and CRANDALL, 1984 ; WOOTON, 1982). These results must therefore be
interpreted as a consequence of important perturbations during rearing which are still not
under control .
With the improvement of larvae and juvenile rearing techniques, the fecundity of
hatchery fish should evolute favourably and reach that of wild fish, as is at present the
case of the sea-bass (COVES, 1986 ; comm. Pers.).
2.5. The effect of feeding
On this particular point, there are numerous results available. Their originality
make them interesting however.
The artificial spawnings carried out on turbot (table 13) do not allow the definition
of the viability rates for the same reasons as those given here above. However, the
results show that turbot, weakened for unknown reasons, don't die as much, when their
food contains vitamins. This treatment has also brought about a 33 % increase in the
relative fecundity of surviving females. This is however not the case when the groups of
turbot appear healthy (NOEL, 1985).
For the sole and the sea-bass (Table 14), the changes in food have no clear
influence on fecundity. The absence of polycheata for sole or the distribution of artificial
food to sea-bass bring about on the other hand a decrease in the viability rate.
With the improvement of artificial food, it appears however that the disadvantage
is not so evident with the sea-bass (SUQUET, 1986).
Therefore, these first observations indicate the interest of following attentively the
relations between rearing environment-food diet and larvae survival. The improvement in
the artificial food for spawners should also be accompanied systematically by larvae
rearing tests so as to detect their effect at more acute levels, than at fecundity or
conformation level of the eggs. The works carried out in fresh water is an example in this
sphere (QUANTZ, 1980 ; LUQUET and WATANABE, 1985).
3. DISCUSSION/CONCLUSION
These results open perspectives for their application in aquaculture, especially
for the spawning alteration techniques, the standardization of units for storing spawners
and the incubation of eggs. On the other hand, like the observations made in natural
environments represent a basis of reflection for the aqua-culturist, the artificial
techniques employed for spawning can be based on the results obtained from natural
reproductions in captivity.
Consequently, today, the adoption of one technique or the other results from the
arbitration based on die species, the rearing zone or simply the material constraints.
Finally, a better knowledge of the methods of reproduction now permits, to stabilize,
increase or stagger as wished (Figure 6) the periods for the production of eggs. But, as
in most of the theoretical or experimental studies carried out on induced reproduction
(HOAR, 1969 ; LILEY, 1980) is to admit that the production of viable embryos results
from a delicate compromise which integrates the action of external and intrinsic factors.
The specific differences should be distinguished especially. Thus, the sole and
turbot don't adapt as well as the gilthead sea-bream and sea-bass in captivity : they
develop parasites more easily ; the annual mortality is on average twice that for seabass and gilthead sea-bream ; finally the viability rate is weaker. On the other hand, the
gametogenesis and the spawning of sole and turbot is suited to low temperatures. As
the confinement in tanks does not permit the fish to escape, abrupt increases in
temperature in Spring and Summer, their apparent inadaptation to captivity could be
linked with unfavourable thermic levels for the species.
Also, gilthead sea-bream, sole and turbot which differ from sea-bass on account
of their numerous ovipositions, have in captivity, a less relative fecundity rate that those
calculated for mature fish caught at sea. Again, let us give precisions on the methods of
estimation : In captivity, fecundity refers to the number of eggs exactly spawned. Due to
this, it is difficult to compare it to the fecundity calculated in natural environments from
the total number of oogonia and ovocytes found in a gonad (DENIEL, 1981), while taking
into account especially that these last waves of ovocytes are often reabsorbed
(LAHAYE, 1972). Thus, logically, the differences between the two values increase with
the number of ovipositions. fecundity in Captivity cannot be therefore stated as
abnormally low.
The age of the animals is also, as is the case for most species, a source for
variation in fecundity. Due to this, the good management of the hatchery for marine fish
is based on the careful choice of the size, weight and ages of spawners. The experience
from salmoniculture (BILLARD, 1986) or of carp breeding (MARCEL) 1986) have also
proven this. It is also interesting to discover that the viability rate and the diameter of the
eggs vary little with the age of the fish.
As for the environment, its effects on reproduction are remarkable. Thus, on the
coast of the La Mancha, from the Atlantic to the Mediterranean, the temperature seems
to be the most determinant extrinsic factor. The respect of the inferior/superior limits,
indeed influences the good evolution of the gameto-genesis and spawning. However,
when the thermic control is difficult, hormonal induction of maturation, by LHRH
especially, can be of great help (BARNABE and BARNABE-QUEST, 1985). The long
term consequences still need precision. On the other hand, certain characteristics of the
eggs (viability rate, hatching rate and malformation rate of larvae with air-bladders) are
also influenced directly by the temperature. Its indirect effects must also be remarked :
by modifying the quantity of food ingested, the temperature can, for example, influence
fecundity, the dates for spawning of the fish (WOOTON, 1982) and as we have
suggested, the biochemical composition and the diameter of the eggs. As for this
parameter, it is interesting to note its evolution, in function of the temperatures registered
at the moment when spawning took place (Figure 7).
Salinity does not need any particular control when within the range 33 - 36‰. In
zones with lots of fresh water, the gametogenesis can however be blocked, especially
with sea-bass (BRUSLE and ROBLIN, 1983 ; ZANUY and CARILLO, 1983). On the
contrary, by reproducing in the Baltic sea, at 15 ‰ (KUHLMANN et al, 1980), turbot
confirm their euryhaline character.
Salinity and temperature also influence the success of incubation. It has been
remarked for the sole and turbot and also for gilthead sea-bream (FREDDI et al, 1981)
and probably for sea-bass as applies for all Teleostei (BLAXTER, 1969 ; HEMPEL,
1979).
Otherwise, all the references (BILLARD, 1979 ; BYE, 1984) show that in
temperate zones, the photoperiod has, along with the temperature, a determinant action
on the gametogenesis. However, the combination between light-conditions and
temperature levels still remain imprecise. The use of recent techniques for biopsies
should help. DEVAUCHELLE (In print) shows also that with turbot, the initiation of the
gametogenesis is almost exclusively controlled by the photo-period, while the
temperature regulates, along with the photoperiod, the speed of the vitel logenesis. It is
evident that the improvement in the techniques of the spawning alteration requires a
progress of knowledge in this sphere. Apart from its effects on maturation, the role of the
photoperiod is not clearly understood (WOOTON, 1982) although an evident direct
influence on the activity level of the fish is remarked.
As for feeding, most authors (Fontaine and OLIVEREAU, 1962; HEMPEL, 1979;
DABROWSKI, 1984) agree on the impact of food rations on fecundities and spawning
dates. The effect on the quality of the eggs, even in extreme conditions is however
controversed (LUQUET and WATANABE, 1985). Not having detailed studies at disposal
on the "special reproduction" food, the normality of the growth curves and conformation
can as far as we are concerned be kept as an indication of good feeding.
On general, the conditions of temperature, salinity or lighting considered as
optimal in a rearing environment, are, in fact, close to these found in normal conditions
of life in natural environments. This has been verified for the gametogenesis, spawning,
incubation, (present study) as well as for other stages of development: for the juvenile
stage of turbot especially (SCHERRER, 1985). Depending on the regulation capacities
of the species, it is indeed not excluded that the optimal conditions for the development
of the parents and in consequence those of the eggs, can vary from one place to
another (BLAXTER, 1969). But all the observations made tend to suggest that the
choice of the rearing techniques should be based on, for each species, at each stage of
development, the previsional effects (survival, malformations, diseases, feeding rate)
that are caused by rearing conditions which differ more and more from normal life
conditions observed in natural environments.
Apart from the biochemical aspects, the production cost of the larvae with airbladders can influence the choice of reproduction strategies. It should therefore be
precised that our working conditions, considered sophisticated, permit a low costing egg
(Table 15) when compared to that of the juvenile. For the moment, the excessive
simplification of production techniques of eggs in the actual state of sea-bass, gilthead
sea-bream, sole and turbot rearing will have little effect on the production cost of
juveniles.
Finally, it should be remarked that only a few of the factors which are liable to
bring success to the hatchery reproduction of marine fish have been discussed here.
The field of investigation in this sphere still remains open. Thus, the effects of the moon
cycles, given phenomena and particular behaviour of each species (LILEY, l980;
COLOMBO et al, 1982 ; TAYLOR, 1984) offer undeniable interesting subjects of study.
But today, so as to better perceive the processes which lead from spawners to
commercial size fish, the most promising approach is to associate the study as much as
possible to the different rearing phases. THe rapid improvement of larval rearing
techniques, those for sea-bass especially (COVES, 1985) has recently allowed this.
Figure 1 : Skeleton diagram of the reproduction tanks, egg collectors and incubators.
Figure 2 : Growth curves of wild fish in natural environments (0), in captivity (.)
and of spawners coming from hatcheries
feeding on fresh or
frozen fish for three or more months.
= first spawning ;
= estimated values ;
= values measured
a) BOULINEAU, 1969 ; b) LASSERRE, 1974 ; c) DENIEL, 1981.
Figure 3 : Size-weight relation of the sea-bass, sole and turbot. The correlations are
calculated according to the BRAVAIS-PERSON. coefficient.
Sea-bass
Sole
Turbot
: y = 0.1824 x + 0.01037
: y = 0.2427 x + 0.26002
: y = 0.192 x + 0.149
Figure 4 : Duration of egg development of turbot (I), sea-bass (II) and sole (III) (of the
fecundation with a 50 % hatching rate of viable eggs) and gilthead sea-bream
(from stage 4 cells to hatching), depending on the incubation temperature .
Between 13 and 17°C, 70 % at least (sea-bass, turbot and gilthead seabream) or 50 % (sole) of viable eggs give birth to normal larvae in our
incubation conditions
a) CAMUS and KOUTSIKOPOULOS, 1984
Figure 5 : Percentages of normal larvae coming From viable eggs of turbot and sole at
temperatures of 12 to l6.5°C and 0 and 35 ‰ of salinity.
0 - 20 %
20 - 50 %
70 – 80 %
80%
50 – 70 %
Tests not carried out
Evolution between 1976 and 1984 of the total weight (Kg) of spawners, of the viability number and rate of the
eggs collected. The objective was, during this period, to maintain a constant level of egg production of seaSD : Altered season bass and sole during an unique season, the normal spawning season and the annual staggering of spawning
SN : Normal season for gilthead sea-bream and turbot. In 1984, the sea-bass spawning lasted for a period of 87 days. The
unfavourable thermic cycle for the emission of eggs of sole, not having been abble to be corrected, their
spawning season was shortened to 28 days. On the contrary, that same year, two tanks of gilthead sea-bream
and three tanks of turbot, having had photoperiod and thermic controls, respectfully reproduced during 218 and
209 days : estimated data .
Figure 6 :
Figure 7 : Relations between the size of the eggs (D) and temperature (T) of the seawater at the moment of spawning. D and T correspond to the punctual and
average values of the data (b to k), from the IFREMER Centre in BREST (a).
a) DEVAUCHELLE, 1980 and our data
b) KENNEDY and FITZMAURICE, 1972
e) BRASOLA, 1974
f) BRASOLA, 1974
g) VILLANI, 1974
h) RAMOS, 1977
j) RAMOS, 1978
k) ALESSIO, 1975
Fish caught at sea
Species
Sea-boss
Conditioning Born in hatcheries
Kg
Years
Kg
Years
Kg
0
0,6
5-8
0,7
4-7
2,5
9 - 12
0
0,8 - 1
“
“
3
10 - 13
1
a
Gilthead Seabream
0
0,5
2-3
0,5
0
0,8 - 1
3-5
0,6a, b
Sole
0
0,5
3-4
0
0,8 - 1
0
0
Turbot
Reform
Years
*
-
3-4
10 - 13
-
1,2
15 - 20
4-5
-
1,5
15 - 20
0,5 - 2
2-4
2
5
8 - 10
“
“
2,5
3-4
4-5
7-8
10 - 12
Table 1 : Choice basis of spawners expressed in weight and age
a : SUQUET, 1986 ; b : ZOHAR et al., 1984
* : Recall that the gilthead sea-bream is protandrous hermaphrodic whose sexual reversion rate is at around 80 %
Species
Fishing techniques
Sea-bass
Line
Gilthead sea-bream – Seine net
Sole
Turbot
Volume of the
tanks
10 - 40
5 - 40
Density
Kg/m3
1,5 - 7
2–7
Seine net
5 - 17
1–3
Drag net of 15 to 30 mm
15 - 40
0,5 - 7
Food
Quality
Fish
Fish
Crabs
Molluscs
Molluscs .
Polycheatae
Fish
Quantity %/S
12
12
10
2
15
Mortality
%/year
2-5
6
5 - 10
Table 2 : Fishing conditions of wild spawners : General indications on the storing conditions. The quantity of food concerns the fresh
weight of food ingested/weight of the spawners x 100 per week.
Species
Selecting+
Stamping Preventive and curative treatment
biopsy gonads
Sea-bass
+a
Indian ink
Copepoda - in reproduction tanks 200 ppm F ±
0.5 ppm VM normal water flow 3
days in succession
- In baths, 500 ppm F - 20 mn
Decrease in salinity
Gilthead sea-bream + a
“
Sole
+a
Monogenic - In small aered volumes 300 ppm
Endobtella solea
+ 1 PPM VM 3 hours
Turbot
+a
Nitrogen
Copepoda - In an aered reproduction tank
without water renewal Neguvon 1
ppm - 2 hours
Trichodina - In baths : 220 ppm F + 0.6 ppm
VM - 20 mn
Metacercaires In baths : 200 ppm F + 0.6 ppm VM
- 20 mn
In big aered tanks with water
renewal : 100 ppm F + 0.3 ppm
VM - 3 times
Table 3 : Principal treatments for spawners
a) DEVAUCHELLE, 1984
b) SUQUET, 1986
Estimations carried out on the day of spawning
SPECIES
Aliquots taken
from the N. of
eggs x 106
Diameter (mm)
Average mini-maxi
Sea-bass
Gilthead Seabream
Sole
Turbot
N. of spawning Incubation
results remarked
Duration of development ° C x
hours - at 150 C
-
Weight
78
71
1,22
1,02
1,07 1,32
0,94-1,05
N. average
Spawning
17
1 030
1 755a
18
91
1,41
1,08
1,2-1,57
0,98-1,18
13
13
690
1 550
N. of Hatching
Spawners of
normal larvae
mini-maxi
811-1 240
3
-
1 215 ± 45
659 ± 18a
10
7
85
85
668-786
1 225-1772
3
3
1 390 ± 91
1 400 ± 46
12
14
74
78
Table 7 : Principal characteristics of the eggs : The tests on incubation took place in incubators of "moteur" type described by
DEVAUCHELLE, 1984, at optimal temperature and salinity levels.
a) DIVANACH, 1985
SPECIES
Sea-bass
Sole
Turbot
Gilthead seabream
Temperature °C
Spawning
Incubation
A
13 - 15
13 - 15
10,5 - 11
11 - 13
13 - 15
13 - 17
15 - 17
14,5a
Incubation
B
13 - 17
11 - 15
13 - 19
-
Duration of the
embryogenesis
(days)
3,6 - 4,6
4,6 - 5,4
5,6 - 3,3
3
Table 8 : Comparison of optimal temperature ranges necessary for spawning and
incubation. For this, two cases ere envisaged :
A : Normal larvae rate 80 %
B : 70 % normal larvae rate 80 %
The eggs placed into incubation are all viable. The duration of the
embryogenesis corresponds to conditions A.
a) CAMUS and KOUTSIKOPOULOS, 1984
SPECIES
N.of
Spawning
Seasons
7
Sea-bass
Gilthead 'Seabream
Sole
6
Turbot
8
7
Duration (days mini maxi (average)
42 - 109
(71)
36 – 154
(107)
13 – 128
(64)
30 – 100
(62)
Spawning
o
T C
9
16
(13 - 15)
12,5/13
24
(15 - 17)
8
12
(10,5 - 11)
9,5
17
(13 - 15)
E (hours)
8,30
16,00
(10 - 14)
8,30
15,30
(9 - 11)
11
16
(11,5 - 12)
10
16,30
(15 - 16,30)
Table 9 : Spawners submitted to thermic and photoperiod controls. Duration of the
spawning season and corresponding ascending descending and stable
temperature and photoperiod conditions.
For the sea-bass, high temperatures (16 - 20 ° C) have been tested : the
results obtained indicate that in favourable lighting conditions (11 - 13
hours|day) the gamatogenesis is blocked when T 21 - 22 ° C. The number of
spawning seasons to which the data relates is equal to the number of annual
cycles.
SPECIES
Sea-bass
Gilthead sea-bream
Sole
Turbot
Minimum duration (months)
- 2,5
-3
-3
-3
- 3,6
T (° C)
20 16
12 - 14
11 - 15
14
10
E (hours)
11
16
11
12
14
15
16,30
16,30
Table 10 : Temperature T and lighting E conditions tested so as to reduce the
gametofenesis time length.
SPECIES
Sea-bass
Sole
Turbot
N. of eggs observed S. N/S.
D x 106
17,6/3,4
4,4/1,2
4,2/8,8
N. of eggs/
spawning %
- 84
- 82
- 55
Survival %
- 17
- 13
- 22
Hatching of viable
eggs %
- 13
- 12
- 30
Table 11 : Maximum reduction observed {%) of the spawning volumes, viability and
hatching of eggs when the reproduction is altered by contraction of the
photoperiod cycles
S.N : Unaltered season
S.D : Altered season
Sea-bass
Sole
Turbot
I
II
III
I
II
III
I
II
III
WATER
PROTEINS
65,2
88,4
89,1
66,8
92
92,1
66,1
91,4
91,6
63,9
54,2
52,6
77,8
62,3
67,8
74,7
76
62,9
LIPIDS % dry
weight
26,2
33,1
26,1
19,1
15,7
13,1
17,8
17,3
15,6
ASHES
4,2
6,2
6,6
5,6
8,1
9,8
4,2
10,6
11,3
Table 12 : Global composition of mature ovules taken from females caught at sea (I),
eggs from gametogenesis, natural spawnings and fecundations, with (I!) or
without (III) the control of the temperature or photoperiod. By DEVAUCHELLE
et al, 1982.
I
II
I
II
TEST 1 (a)
Density
N. of fish
Kg/m3
12
4,1
12
3,2
12
3
12
2,7
Origin
Treatment
TEST 2 (b)
N. of fish
P.M. Kg
S+E
S+E
I
II
Origin
Treatment
SAUVAGE
(S)
ECLOSERIE
(E)
32
32
3,3
3,3
N N. of N. of eqqs
dead fish Kg° °x 106
5,15 ± 1,43
1
408
4,56 ± 1,62
7
278
4,19 ± 1
2
299
3,86 ± 0,83
1
163
P.M. (Kg)
N. of dead fish N. of eggs/Kg of
larvae ° X
0
12,7
0
22,8
Table 13 - Effect of the origin (Test 1) and of feeding (Test 1 and 2) of turbot on the
production of larvae and eggs, per Kg of female.
–
The food consists of pieces of fish distributed ad libitum with (I) or without
(II) vitamins (C, E, B, B6, Biotine and Inositol) at a rote of 1 mg/Kg of
fish/week (METAILLER, comm. pers., 1985). The average weekly
consumption (wet weight of the food/weight of spawners) is 2 % (test 1)
and 4 % (test 2)
–
The treatment I also involves an intraperitoneal injection of vitamin C (100
mg/Kg of fish) 3 months before spawning cakes place. The storing tanks
have a volume of 20 m3 (test 1) and 30 m3 (test 2)
SPECIES
Period
Sea-bass
1976
1977
Sole
1976
1982
1983
1984
Food
I
II
III
IV
N. of fish at the
beginning
20
30
30
60
V
66
Density Kg/ m3 Mortality/ Year % N. of eggs collected Average viability rate,
x 10
considered
1,2 - 1,5
0
81
89
“
0
143
57
“
0
52
86
2,5 - 3,1
5,7
9 600
77
"
5,3
5 200
Table 14 : Effect of food given to sea-bass and sole on the quality of the eggs.
Sea-bass : I = pieces of fish - II = dry food - III = mixed food (fish + dry food), DEVAUCHELLE, 1980.
Sole :
IV = molluscs (M) and polychaeta (P)
Average net weight of the food ingested/Kg of fish/week (C) = 10 % (M) + 2 % (P) ;
V = Molluscs, C = 12 %
54
SPECIES
Sea-bass
Gilthead seabream
Sole
a
b
Turbot
Annual cos
Production of 107
Upkeep of a 10 m3
viable eggs (F.F)
tank (F.F)
21 000
6 700
5 500
7 000
46 000
140 000
8 300
3 500
10 500
9 200
Pumping
Food
Group
35
21
36
21
29
58
38
11
45
44
83
46
17
5
9
Table 15 : The cost price of eggs, not counting salaries nor depreciation, in normal
spawning seasons, calculated on the basis of 3 Kg of spawners per m3 of sea-water.
The cost of the eggs of sole varies in function of the food ; molluscs alone (a) or
molluscs and polychaeta (b). The 10 m3 tanks represent an interesting unit for the
hatchery, its upkeep price is indicated. In the Brittany region, the spawning alteration
based on a thermic and photoperiod control doubles the price of the egg.
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LARVAL SHRIMP FEEDING
CRUSTACEAN TISSUE SUSPENSION : A PRACTICAL ALTERNATIVE FOR SHRIMP
CULTURE
Mr. A.G.J. TACON
1. INTRODUCTION
1.1 Context and Purpose of Report
Four different live planktonic food organisms (diatoms, flagellates, rotifers and
Artemia nauplii) are commonly used for the mass propagation of penaeid shrimp larvae
from protozoea substage 1, through metamorphosis, to the post-larval substage. Modern
penaeid shrimp hatcheries are therefore dependent on highly trained and skilled labour,
and sophisticated live food production systems which require high capital investment in
terms of space, facilities and services, and even expensive feed procurement, such as
Artemia cysts.
A modern, well-managed, shrimp hatchery using live food feeding strategies can
be economically efficient. However, there is a need to develop a simple and inexpensive
feeding strategy which can be readily adopted by the owner-operator or rural farmer with
limited resources. This report is an evaluation of a simple and inexpensive hatchery
feeding strategy originally developed in India. Based on the exclusive use of a
crustacean tissue suspension throughout the hatchery cycle, this feeding strategy was
tested on Penaeus monodon in a series of trials at the Regional Lead Centre in the
Philippines, based at the Southeast Asian Fisheries Development Centre's (SEAFDEC)
Aquaculture Department.
1.2 The Mission
The purpose of the mission was: (a) to collate published information on the use
of crustacean wet tissue suspension for larval feeding, and determine the relative merits
and demerits of the feeding strategy; (b) to discuss recent . developments in larval
shrimp feeding with research staff at the Central Marine Fisheries Research Institute
(CMFRI) in Cochin (February, 1985); (c) to travel to the Regional Lead Centre in the
Philippines (part of the Network of Aquaculture Centres in Asia, NACA) and assist Mr. P.
Kungvankij, NACA Aquaculturist (Research) in planning and executing larval feeding
trials incorporating the suspension with P. monodon. The work was to be performed at
the Leganes Hatchery, SEAFDEC Aquaculture Department, Iloilo, Philippines (MarchApril, 1985).
1.3 Acknowledgements
The author would like to thank Dr. T.V.R.Pillay (former Programme Leader,
ADCP) and Mr. P.G. Padlan (Senior Aquaculturist, ADCP) , for identifying the mission.
Valuable experimental information was provided by Dr. E.G. Silas (Director, CMFRI) and
his research staff at Cochin, India. The larval feeding trials conducted at SEAFDEC
Aquaculture Department were achieved with the enthusiastic cooperation and sustained
hard work of Mr. P. Kungvankij, NACA Aquaculturist (Research) and his SEAFDEC
research colleagues at the Leganes Hatchery, including Mr. E. Borlongan, Ms. K.G.
Corre, Ms. L.F. Gustilo, Mr. I,O. Potestas, Mr. B.J. Pudadera, Ms. G.A. Taleon, and Mr.
A. Unggi. The author is also grateful to many other private persons and officials of NACA
and SEAFDEC, and especially to Dr. F.P. Pascual (Nutritionist) of the latter agency for
her untiring support and cooperation as a friend and fellow nutritionist.
2. BACKGROUND
Almost all commercial penaeid shrimp hatchery operations rely on the exclusive
use of a succession of live food organisms (commonly diatoms, algae, rotifers and
Artemia nauplii) for the larval culture cycle (for review see CRC, 1983; Liao, 1984). This
practice is due to the lack of a suitable alternative feeding method. Until recently,
previous attemps to replace live food organisms completely with artificial dry diets have
generally led to poor larval survival and delayed larval development (New, 1976).
Two new feeding systems have been introduced recently as 'viable' alternatives
to the live food production system: (1) the exclusive use of a rehydratable
microencapsulated/microbound larval shrimp diet (Jones, 1984; Scura, Fischer and
Yunker, 1984; Kanazawa, 1983), and (2) the exclusive use of a crustacean tissue
suspension (Hameed Ali, Dwivedi and Alikunhi, 1982). Although both methods rely on
feeding a single, non-living food for the entire larval culture phase, they differ in the feed
resources used and the degree of sophistication of feed preparation. This report is
concerned with the evaluation of the crustacean tissue suspension feeding strategy.
3. CRUSTACEAN TISSUE SUSPENSION - REVIEW OF PAST INDIAN STUDIES
A novel and inexpensive hatchery feeding system has been used for the mass
rearing of penaeid shrimp larvae in India (Hameed Ali, Dwivedi and Alikunhi, 1982). The
system is based on the exclusive use of a crustacean wet tissue suspension as a feed
for all larval and early post-larval (PL) stages. It has been developed from a series of
feeding trials conducted at the Central Institute of Fisheries Education (Bombay), the
Brackishwater Aquaculture Development Centre in Jepara (Indonesia), the Regional
Shrimp Hatchery at Azhicode (Kerala), and the Mundra Experimental Shrimp Hatchery,
Gujarat (Alikunhi et al., 1980, 1982; Hameed Ali, 1980; Hameed Ali and Dwivedi, 1977;
Hameed Ali, Dwivedi and Alikunhi, 1982).
Crustaceans which have been successfully processed into a wet tissue
suspension for the trials include the Jinga shrimp, Metapenaeus affinis; Kadal shrimp, M.
dobsoni ('Thelli'); Kiddi shrimp, Parapenaeopsis stylifera; Jawla paste shrimp, Acetes
indicus; Spider prawn, Nematopalaemon tenipes; mysids Mesopodopsis spp; and the
stomatopod crustacean, Oratosquilla nepa 'Chelly'. The choice of crustacean is based
on local availability, ease of capture by fishermen and on market cost. The commonest
crustaceans used have been the Jawla paste shrimp, the stomatopod and the Kadal
shrimp. Table 1 shows the feeding regime recommended by Hameed Ali, Dwivedi and
Alikunhi (1982) for the individual larval stages of Penaeus spp., Metapenaeus spp., and
Parapenaeopsis spp., using a crustacean wet tissue suspension.
Feeding trials in India have been conducted with nine shrimp species: Penaeus
monodon, P. merguiensis, P. indicus, P. semisulcatus, Metapenaeus affinis, M.
monoceros, M. brevicornis, M. dobsoni and Parapenaeus stylifera (for review see
Hameed Ali, Dwivedi and Alikunhi, 1982). All the nine shrimp species were reared
successfully on the wet tissue suspension from Z1 stage, through metamorphosis, to the
early PL stage. Of the different suspensions evaluated, 'Chelly' (O. nepa) gave higher
larval survival than 'Thelli' (M. dobsoni) with P. indicus and P. monodon (Alikunhi et al.,
1980). Hameed Ali, Dwivedi and Alikunhi (1982) estimate that over 150 million penaeid
larvae have been reared using this feeding system, with the production of over 50 million
early penaeid larvae. This is an overall survival rate from N6 to PL1 of about 33 percent.
Alikunhi et al., (1980) obtained a mean larval survival from N6 to PL1 of 43.8% for P.
indicus (78 separate culture runs), 25.3% for P. monodon (x7), 72.0% for P.
semisulcatus (x2), 32.9% for M. monoceros (x2), 62.5% for M. dobsoni (x3) and 30.8%
for P. stylifera (x2) using either a 'Chelly' or 'Thelli' suspension between 1979 and 1980.
However, although many individual cultures had over 90% survival, with larval PL
productions exceeding 200 PL1/1, 18 from a total of 114 cultures successfully
implemented at the N6 substage had to be discarded during the larval growth phase due
to the development of intense diatom blooms within the tanks. As these failures
invariably occurred within rearing tanks exposed to direct sunlight, they were not
assumed to be caused by the feeding regime itself, and consequently were not included
by Alikunhi et al., (1980) in their final estimations of larval survival. However, these
failures represent a 15.8% loss of all cultures. Hameed Ali (1980) and Hameed Ali,
Dwivedi and Alikunhi (1982) also reported the development of algal and diatom blooms
within the culture tanks during larval production.
Although Alikunhi et al., (1980) and Hameed Ali (1980) state that the shrimp
larvae are fed exclusively on a non-living diet, the fact that algal/ diatom blooms occur in
the culture tank indicates the presence of potential live food organisms for the shrimp.
Similarly, although they state that no larval mortalities occurred due to overfeeding with
the tissue suspension, they do not comment on the fact that the diatom blooms present
may have resulted directly from the nutrients provided in the feeding system used
(fertilizing effect). If this is the case, culture losses attributed by Alikunhi et al., (1980) to
excessive diatom blooms may have been due to over-feeding and insufficient water
exchange.
4. CRUSTACEAN TISSUE SUSPENSION - LEGANES FEEDING TRIALS
4.1 Introduction
On the basis of the very encouraging results obtained by Hameed Ali and coworkers in India with a crustacean tissue suspension for larval feeding, and after
discussion with Dr. E.G. Silas and Mr. P. Kungvankij, three experimental feeding trials
were conducted with first feeding P. monodon larvae at the Leganes Hatchery,
SEAFDEC Aquaculture Department, Iloilo (10 March to 4 April, 1985).1/ In addition to the
'wet' crustacean tissue suspension feeding system used by Hameed Ali, Dwivedi and
Alikunhi (1982), a new 'dry' crustacean tissue suspension feeding system was also
tested.
1
Broodstock management, larval rearing and live food production was conducted by Mr. P. Kungvankij with the assistance
of his SEAFDEC research colleagues at the Leganes Hatchery, including Mr. E. Borlongan, Ms. K.G. Corre, Ms. L.F.
Gustilo, Mr. I.O. Potestas, Mr. B.J. Pudadera, Ms. G.A. Taleon, and Mr. A. Unggi
Crustacean tissue suspensions were prepared from the sergestid shrimp, Acetes
sp., known locally in the Philippines as 'Alamang'. This species was chosen because of
its local market availability in Iloilo at the time of the Mission and because this shrimp
family constituted one of the original feed sources used by Hameed Ali and co-workers
for the preparation of a crustacean wet tissue suspension (Jawla paste shrimp - Acetes
indicus; Hameed Ali, et al., 1982).
Table 1
Feed Particle Size and Feeding Regime Recommended for the Larval Rearing of
Shrimp using a Crustacean Wet Tissue Preparation
Penaeus spp.
Feed particle size (μm)
during Protozoea Z1
160
Z2
160
Z3
200
Mysis
M1
250-300
M2
300-400
M3
300-400
Post Larval
PL1
400-500
Optimum feed dosage Squilla*
Others
(g raw material/1 000
larvae/day)
during Protozoea Z1
1.0
0.5
Z2
1.25
0.75
Z3
1.5
0.75
Mysis
M1
1.75
1.0
M2
1.75
1.25
M3
2.0
1.5
Post Larval
PL1
2.0
2.0
Shrimp Species Reared
Metapenaeus spp.
Parapenaeopsis spp.
50
50
160
160
250-300
250-300
300
Squilla
Others
50
50
160
160
250-300
250-300
300
Squilla.
Others
0.5
0.75
1.0
1.25
1.25
1.5
1.75
0.5
0.75
1.0
1.25
1.25
1.5
1.75
0.3
0.5
0.6
0.75
1.0
1.25
1.5
0.3
0.5
0.6
0.75
1.0
1.25
1.5
* due to its thick exoskeleton, compared with other feed crustaceans, higher feed levels are administered
Source: Hameed Ali et al., 1982 M1
4.2 Materials and Methods
Three successive feeding trials, code-named A, B and C, were performed with
first feeding P. monodon larvae obtained from wild-caught spawners. The feeding trials
were conducted in either outdoor larval rearing tanks (experiments A and C) or in indoor
larval rearing tanks (experiment B). In experiment A six different feeding regimes were
tested (I-VI, Fig. 1); four crustacean tissue feeding options, including the original frozen
crustacean feeding strategy described by Hameed Ali, et al., (1982), and two 'control'
live food feeding options similar to those normally employed at the Leganes Hatchery.
The three most successful feeding options observed during experiment A were then
evaluated within indoor tanks in experiment B and again in outdoor tanks in experiment
C, although in the latter case an additional 'control’ group receiving no exogenous live or
artificial feed input was also introduced.
4.2.1 Experimental Larval Rearing Tanks and Water Management
Two experimental rearing facilities were used for the three larval feeding trials. In
experiments A and C larval rearing was conducted in twelve 1 000 1 circular fibreglass
phytoplankton production tanks situated outdoors. These tanks were covered by a
translucent tarpalion from midday until the following morning so as to minimize
fluctuations in water temperature. In experiment B larval rearing was conducted in nine,
250 1 circular fibreglass spawning tanks situated indoors within the hatchery building at
Leganes. These tanks were positioned adjacent to a frosted glass window and received
only natural lighting, A diagramatic representation of the two experimental tanks systems
is shown in Fig. 2.
A non-continuous water management system was adopted within the larval
rearing tanks throughout the culture cycle; a pre-determined percentage of the total
volume of water within the tank being exchanged once daily at 08.00 h by siphoning
(using a box filter) and then replenishing with an equal volume of fresh filtered (15 μm)
sea water. The proportion of water replaced daily was dependent upon the
developmental status of the larvae present. The water management procedures adopted
during the three feeding trials are shown in Table 2.
Throughout the larval feeding trials continuous aeration and water upwelling was
maintained within the culture tanks by means of a single aerator placed centrally at the
bottom of each tank. Each aerator consisted of a bottom weighted, open ended, PVC air
distribution line connected to a central Roots air blower. Water circulation and agitation
was essential so as to maintain the shrimp larvae and food organisms tested in constant
suspension within the water column.
4.2.2 Experimental Animals
Mature, ready-to-spawn, P. monodon broodstock were collected daily from local
fishermen and individually placed (when tank space permitted) into 250 1 circular
fibreglass spawning tanks within the hatchery building. Each spawning tank contained
around 200 1 of fresh seawater (26-29 C, 34-36 ‰ salinity, previously filtered through a
15 μm bag net filter), was aerated by a single PVC air distribution line, and was covered
by a removable plywood lid. On spawning, which usually occurred at night, the spent
female was removed and the fertilized eggs siphoned from the water column into a
plastic egg collector consisting of two successive sieves; firstly a 250 μm sieve for
retaining unwanted debris, and secondly a 80 μm sieve for retaining the fertilized eggs.
Eggs from single spawnings collected in this way were subsequently washed with
filtered seawater and then immersed in a bath of methylene blue (2 mg/1), before being
re-suspended in fresh filtered sea water within the spawning tank (or hatching tank as it
was now called). On hatching, the shrimp nauplii were counted by taking replicate 100
ml water samples, and then transferred to the experimental rearing tanks for the
commencement of the different larval feeding trials. Initial nauplii stocking density within
the larval rearing tanks varied between 60-100 nauplii/l (experiments A and C) and 150200 nauplii/1 (experiment B). During each experiment the larvae were reared from the
nauplius stage (N1) to the M3/P1 stage for a total of 10-12 days using one of six different
feeding regimes.
Fig. 1 Feeding Schemes tested with P. mondon larvae
a.
b.
Fig. 2 – Larval tanks employed during Experiments A and C (a) and B (b)
Table 2
Water Management Procedures employed during1
Experiments A, B and C
Larval Stage
A
N1-3
N3-6
Z1
Z2
Z 2-3
Z3
M1
M2
M3
1
700
700
700 + 200
900 ± 300
900 ± 400
900 ± 400
900 ± 400
900 ± 400
900 ± 400
Experiment
B
200
200
200 ± 60
200 ± 160
200 ± 160
200 ± 160
200 ± 160
200 ± 160
200 ± 160
C
700
700
700 + 150
850 ± 250
850 ± 350
850 ± 350
850 ± 400
850 ± 500
850 ± 450
First value represents water volume (1) in larval rearing tank, and second value represents daily water management at
0800 h.
4.2.3 Food and Feeding Regimes
Experiment A
Six different feeding regimes were tested (I-VI; Fig. 1).
A-I
Culture live food feeding option:
Tetraselmis sp. (Batan strain) fed so as to maintain a concentration of around 10
000 cells/ml throughout the culture cycle from day 2 after hatching (N 3-6) to
M3/P1. Brachionus plicatilis fed to maintain a concentration of five organisms/ml
from Z3 to M3/P1. Artemia salina nauplii fed to maintain a concentration of two
organisms/ml from M2 to M3/P1.
A-II
Fertilization/live food feeding option:
Inorganic fertilization of water throughout the culture cycle to encourage the
growth of a mixed diatom population - daily dosage of fertilizer included 4/0.4
mg/l of NaNO3/NaH2PO4 respectively at day 1 (N1-3) and thereafter at 3/0.3 mg/1
until M3/P1. The technical grade fertilizers commonly used at Leganes are
KNO3/Na2HPO4,however no stocks were available at the time of this Mission. In
addition to inorganic fertilization, B. plicatilis and A. salina nauplii were fed at 5
organisms/ml from Z3 to M3/P1 and 2 organisms/ml from M2 to M3/P1 respectively.
The algae, rotifer and Artemia culture methods employed have been described
previously by Kungvankij et al., (1984).
A-III
Frozen Acetes feeding option:
Fresh Acetes sp. was obtained from local fishermen and stored at -200 C. The
feeding regime employed was based on an initial feeding rate of 0.5 mg frozen
Acetes/larvae/day at N 3-6 and Z1 (day 2 and 3 after hatching), thereafter
increasing the feeding rate by 20%/day until M3/P1. Feeding rates were
calculated assuming 100% larval survival so as to ensure a minimum feed
particle concentration within the water column. The feed suspension was
prepared by homogenizing one day's feed requirement with an appropriate
volume of sea water in an electric blender, and passing the homogenate through
appropriate mesh sieves to obtain the required particle size range for the larvae;
<125 μm N6-Z2/3; 125<250 m/μ Z3-M2; 250<350 mμ M3-p1.
A-IV
Fertilization/frozen Acetes feeding option:
As above but also including the inorganic fertilization regime described under AII.
A-V
Dry Acetes feeding option:
Air/sun-dried Acetes was obtained from the local food market in Iloilo City and
ground to a free-flowing powder of appropriate particle size (50<125 mμ N6-Z2/3;
l25<250 μm Z3-M2; 250<350 μm M3-P1<) by using a hammermill. An initial
feeding rate of 0.10 mg dry Acetes/larvae/day (Ξ 0.50 mg frozen
Acetes/larvae/day) was employed at N3-6 and Z1 (days 2 and 3 after hatching),
thereafter increasing by 20%/day until M3 /P1. The proximate composition of the
Acetes used is shown in Table 3.
Table 3
Proximate Composition of Air/Sun-Dried Acetes sp. sample used in
Experiment A and over the period March 1977-July 19821
Component
(%)
14 .09
Acetes sample
March 1977 - July 1982
Range
3.5 - 14.0
54.46
3.74
4.88
15.20
21.72
3.44
1.25
55.45 - 72.78
4.13 - 5.77
2.67 - 8.09
7.34 - 25.42
NA4
NA
NA
Experiment A
Moisture
Dry Matter Basis (%)
Crude protein (N x 6.25)
Crude lipid
Crude fibre
Ash
NFE3
Calcium
Phosphorus
1
Analyses provided by the Analytical Laboratory Division of SEAFDEC Aquaculture Department
2
Mean of five samples
3
Nitrogen free extractives = 100-(Moisture + crude protein + lipid + ash + crude fibre)
4
Not available
A-VI
Mean2
7.94
67.59
5 .04
4.97
16.29
6.11
NA
NA
Fertilization/dry Acetes feeding option:
As A-V but including the inorganic fertilization regime described under A-II.
Experiment B
Three different feeding options were tested:
B-I
Cultured live food feeding option:
As for experiment A, but also including the feeding of the diatom Chaetoceros
calcitrans so as to maintain a cell concentration of around 50 000/ml throughout
the aquaculture cycle from N3-6 (day 2 after hatching) to M3/P1 (in addition to the
flagellate Tetraselmis sp.)
B-II
Frozen Acetes feeding option:
As for experiment A, but feeding rate adjusted to actual number of larvae
present/day until Z3, thereafter feeding rate estimated on basis of original larvae
stocked at N3-6 (i.e. feeding rates from N3-6 -Z3 were not based on 100% survival,
but on actual numbers observed).
B-III
Dry Acetes feeding option:
As for experiment A, but feeding rate adjusted as above.
Experiment C
Four different feeding options were tested:
C-I
Cultured live food feeding option:
As for experiment B
C-II
Frozen Acetes feeding option:
As for experiment A
C-III
Dry Acetes feeding option:
As for experiment A
C-IV
Control bank feeding option:
No cultured algae or exogenous dry/live food input; larval growth being totally
dependent on the natural plankton community within filtered sea water.
4.2.4 Management
In experiment A the study consisted of six dietary treatments with two replicates
per treatment, in experiment B, three dietary treatments with three replicates per
treatment, and in experiment C, four dietary treatments with three replicates per
treatment. In all the three feeding trials the treatments were randomly assigned to the
experimental larval rearing tanks.
Feeding commenced immediately after water management in all cases (4.2.1),
once daily at 0830 h for the cultured algae, live food and inorganic fertilization feeding
options, and four times daily for the frozen/dry Acetes feeding options (0830, 1200, 1700
and 2400 h; the daily feed allowance being divided into four equal Darts).
Plankton counts, water temperature, pH and salinity readings were performed in
each culture tank before water management (0800 h) and in the afternoon (1500 h) on a
daily basis. Since there was little or no variation observed between individual tanks on
the basis of the chemical water quality parameters monitored, the ranges and mean
values recorded over the entire experimental culture cycle are shown in Table 4.
Table 4
Temperature, pH and Salinity of Seawater within Culture Tanks during Experiments A, B
and C
Experiment
A
B
C1
1
Temperature (0C)
Mean
Range
28.5
24-32.5
27.0
25.6-28.4
30.1
28-31.5
pH
Mean
8.0
8.2
8.4
Range
7.5-8.7
7.9-8.5
8.2-8.6
Salinity (‰)
Mean
Range
34.6
34-36
35.3
34-37
36.1
34-37
Data based only up to Z3 stage or day 6 after hatching
Replicate 1 litre water samples were also collected immediately after water
management for the estimation of larval numbers and stage of development. In addition
to the above routine activities, plankton counts were also monitored in one control tank
containing no shrimp larvae and receiving no feed input during experiment A so as to
ascertain background plankton levels.
4. 3 Results
4.3.1 Experiment A
The larval count, growth and survival rate of P. monodon larvae over the 10-day
culture cycle is shown in Table 5 and Fig. 3. The highest mean survival rare was
recorded for the dry Acetes feeding option - 46.7%, followed by frozen Acetes - 29.4%,
cultured live food - 24.7%, fertilization/dry Acetes - 16.6%, fertilization/live food and
fertilization/frozen Acetes - 16.0%. Larval development was similar In all treatments, with
the exception of feeding regimes utilizing frozen Acetes, which by day 10 (0600 h) had
still not metamorphosed from the third mysis substage to the first post larval substage
(Fig. 3).
A histogram representing the phytoplankton community within the larval rearing
tanks is shown in Fig. 4. Although it; was not; possible to monitor the phytoplankton
community throughout the entire 10-day larval culture cycle, all treatments displayed a
higher phytoplankton community than the control tank containing no larvae and receiving
no teed input. Highest phytoplankton levels were generally observed before the start of
the water management programme (Table 2), i.e., on day 3 or the morning of day 4 after
hatching. The most dominant species present within all treatments was the solitary or
chained form of the diatom Chaetoceros calcitrans. Surprisingly, no beneficial effect of
Inorganic fertilization was evident in those treatments receiving Acetes inputs.
Table 5 - Larval count and development of P. monodon larvae on six different feeding
regimes in outdoor tanks - Experiment A1/
Cultured live food (A-I)
Total
Days
Replicate I
Replicate II
water
after
Total
Larval
Larval
Total
Larval Larval
volume
hatching
larval
stage
density
larval
stage density
(1)
count
(No./1) count
(No./1)
2
700 57 750 N3-6
82 43 400 N3-6
62
3
900 58 500 Z1
65 54 000 Z1
60
4
900 75 600 Z2
84 42 300 Z2
47
5
900 48 600 Z2-3
54 36 000 Z2-3
40
6
900 54 900 Z3
61 28 800 Z3
32
7
900 53 100 M1
59 30 600 M1
34
8
900 47 175 M2
52 28 475 M2
32
9
900 33 575 M3
37 25 500 M3
28
10
900 15 000 P1
17 16 000 P1
18
Survival rate (%)
19.8
29.6
Mean survival
24.7
rate (%)
Fertilization/live food (A-II)
Replicate I
Replicate II
Total Larval Larval Total Larval Larval
larval stage density larval stage density
count
(No./1) count
(No./1)
58 450 N3-6
83
44 100 N3-6
63
62 100 Z1
69
32 850 Z1
36
68 400 Z2
76
32 400 Z2
36
62 100 Z2-3
69
28 800 Z2-3
32
40 500 Z3
45
18 900 Z3
21
26 100 M1
29
22 500 M1
25
8 925 M2
10
8 500 M2
9
4 250 M3
5
11 475 M3
13
200 P1
0.2 14 000 P1
16
0.32
31.7
Days
Total
Frozen Acetes (A-III)
after
water
Replicate I
Replicate II
hatching volume Total Larval Larval Total Larva Larval
(1)
larval stage density larval
l density
count
(No./1) count stage (No./1)
Fertilization/Frozen Acetes (A-IV)
Replicate I
Replicate II
Total Larva Larval Total Larva Larval
larval
l
densit larval
l
densit
count stage y
count stage
y
(No./1)
(No./1)
55.300 N3-6
79 49 700 N3-6
71
57 600 Z1
64 18 900 Z1
21
52 200 Z2
58 12 000 Z2
13
45 900 Z2-3
51
9 900 Z2-3
11
45 000 Z3
50
9 900 Z3
11
35 100 M1
39
8 000 M1
9
29 600 M2
33
9 775 M2
11
21 675 M3
24
6 800 M3
8
8 000 M3/P1
9
9 000 P1
10
13.9
18.1
2
700
3
900
4
900
5
900
6
900
7
900
8
900
9
900
10
900
Survival rate (%)
Mean survival
rate (%)
52 850
60 750
63 000
48 650
49 500
44 100
36 875
49 725
22 000
N3-6
Z1
Z2
Z2-3
Z3
M1
M2
M3
M3
34.9
75
67
70
54
55
49
41
55
24
51 450
66 600
45 900
41 400
42 300
37 800
41 650
39 525
16 000
29.4
N3-6
Z1
Z2
Z2-3
Z3
M1
M2
M3
M3
24.0
73
74
51
46
47
42
46
44
18
16.0
16.0
Days
Total
after
water
hatching volume
(1)
Dry Acetes (A-V)
Replicate I
Replicate II
Total
Larval Larval Total Larval Larval
larval
stage density larval stage density
count
(No./1) count
(No./1)
Fertilization/Dry Acetes (a-VI)
Replicate I
Replicate II
Total Larval Larval Total
Larval Larval
larval stage density larval stage density
count
(No./1) count
(No./1)
2
700
3
900
4
900
5
900
6
900
7
900
8
900
9
900
10
900
Survival rats (%)
Mean survival
rate (%)
47 250
54 900
62 100
62 100
45 900
55 800
56 950
48 450
32 000
69 900 N3-6
68 850 Z1
60 300 Z2
54 900 Z2-3
59 500 Z3
47 700 M1
31 450 M2
37 825 M3
10 000 P1
14.3
N3-6
Z1
Z2
Z2-3
Z3
M1
M2
M3
P1
51.5
67
61
69
69
51
62
63
54
36
46.7
2/ Very poor survival due to Vibrio infection at Z
3
45 850
54 900
62 100
46 800
37 800
49 500
49 300
36 975
26 000
N3-6
Z1
Z2
Z2-3
Z3
M1
M2
M3
P1
41.9
65
61
69
52
42
55
55
41
29
100
76
67
61
66
53
35
42
11
52 500
50 850
47 700
45 000
39 600
33 300
28 475
11 900
10 000
N3-6
Z1
Z2
Z2-3
Z3
M1
M2
M3
P1
19.0
75
56
53
50
44
37
32
13
11
16.6
Note: the discrepancy in total counts during the
early stages of development were due to the
sampling difficulties involved with counting large
numbers of very small larvae
Fig. 3 - Growth and survival rate of P. monodon larvae on six different feeding regimes in outdoor tanks - Experiment A
Fig. 4 Histogram representing the phytoplankton community within the larval rearing tanks during Experiment A (each day is
sub-divided into a.m. and p.a. counts)
Note: Blank spaces indicate that no samples were taken on these days
4.3.2 Experiment B
The larval count, growth and survival rate of P. monodon larvae over the 11-day
culture cycle is shown in Table 6 and Fig. 5. In contrast to Experiment A, all treatments
displayed a low survival rate during this culture trial. Although these differences may
have resulted from variations in egg quality between individual spawners, this trial was
performed in indoor tanks and with double the initial larval stocking density used in
experiment A (147-192 larvae/1 as compared with 62-100 larvae/1). The highest mean
survival rate (calculated after 10 days of culture) was recorded for the frozen Acetes
feeding option - 12.7%, followed by cultured live food - 9.5% and dry Acetes -8.2%.
However, these differences were not significantly different (p<0.05). Within the Acetes
feeding options larval mortality was seen to stabilize once the zoea 3 substage had been
reached. Interestingly, the Acetes feeding regime employed was changed during the
zoea 3 substage from a daily feeding rate based on the actual number of larvae present
within the culture tank to a saturation daily feeding rate based on the original number of
larvae stocked at day 1 (i.e. so as to maintain a minimum number of feed particles/unit
volume of water).
Larval development was found to be delayed by at least one day for all
treatments receiving Acetes as a feed input; metamorphosis from the zoea to the mysis
substage requiring one additional day (Fig. 5). Furthermore, all larvae fed with Acetes
(frozen or dry) were noticeably smaller than the corresponding larvae fed culture live
food.
A histogram representing the phytoplankton community within the larval rearing
tanks is shown in Fig. 6. In contrast to experiment A, the phytoplankton community
within tanks receiving cultured live food was many times greater (i.e. cells/ml) than the
levels observed within the Acetes treatments, due to the introduction of the diatom C.
calcitrans into the cultured live food feeding option. Although larval tanks were not
exposed to direct sunlight, the phyto-plankton levels present were of the same order as
those observed during experiment A for tanks receiving dry or frozen Acetes inputs (Fig.
4). The most dominant species present within all treatments was the solitary diatom C.
calcitrans and not the chained form. Two new species were also present; the food
diatom Navicula sp. and an unidentified blue green algae (although absent within
treatments receiving frozen Acetes, Fig. 6).
4.3.3 Experiment C
The larval count, growth and survival rate of P. monodon larvae over the 9-day
culture cycle is shown in Table V and Fig. 7. As observed during experiment A, the
highest mean survival rate was recorded for the dry Acetes feeding option - 40,6%,
followed by frozen Acetes - 10.3% and cultured live-food - 7.8%. No mean survival data
are available for the control - no feeding treatments as all tanks were discarded on day
9: the survival rate for two-replicates at day 8 being 5.5 and 17.1% respectively at the
mysis 2 substage (Table 7). However, ail non-fed larvae were visibly small and weak
during the mysis substage. Despite the high survival rate of larvae fed the dry Acetes
feeding option, larval development; was one day behind (for two out of the three
replicates) that of larvae fed the cultured live food feeding option which reached the
mysis 2 substage after only 7 clays from hatching (Table 1). Unfortunately, no
phytoplankton data are available for comment.
Table 6 - Larval count and development of P. monodon larvae on three different feeding
regimes in indoor tanks - Experiment: B1/
Feeding option tested: cultured live food (B-1)
Replicate I
Total
Larval
larval Larval density
count stage (No./I)
1
29 500 N1-3
147
2
30 000 N3-6
150
3
25 000 Z1
125
4
19 000 Z2
95
5
10 000 Z2-3
50
6
9 700 Z3
48
7
2 600 M1
13
8
3 600 M2
18
9
2 000 M3
14
10
2 500*P1
12
11
*Transferred (0730) to
outdoor tanks
Survival rate (%)
8.3
Mean survival rate (%) 9.5
Feeding option tested: frozen Acetes (B-II)
1
200 35 500 N1-3
177
2
200 32 000 N3-6
160
3
200 23 000 Z1
115
4
200
7 000 Z2
35
5
200
6 000 Z2-3
30
6
200
3 400 Z3
17
7
200
3 600 Z3-M1
18
8
200
3 200 M1
16
9
200
3 600 M2
18
10
200
3 000 M3
15
11
200 No data available
Survival rate (%)
8.4
Mean survival rate (%) 12.7
Feeding option tested: dry Acetes (B-III)
1
200 35 500 N1-3
177
2
200 30 300 N3-6
151
3
200 23 500 Z1
117
4
200 18 500 Z2
92
5
200
5 000 Z2-3
25
6
200
3 400 Z3
17
7
200
4 200 Z3
21
8
200
2 800 M1
14
9
200
3 000 M2
15
10
200
2 700 M3
13
11
200 No data available
Survival rate (%)
7.6
Mean survival rate 8.2
Days
after
hitching
Total
water
volume
(1)
200
200
200
200
200
200
200
200
200
200
200
Replicate II
Total
Larval
larval Larval density
count stage (No./I)
38 500 N1-3
192
30 000 N3-6
150
21 000 Z1
105
20 000 Z2
100
17 000 Z2-3
85
11 200 Z3
56
9 600 M1
48
9 600 M2
48
6 300 M3
31
4 200* P1
21
*Transferred (0730) to
outdoor tanks
10.9
Replicate III
Total
Larval
larval Larval density
count stage (No./I)
32 000 N1-3
160
31 500 N3-6
157
15 500 Z1
77
11 000 Z2
55
13 000 Z2-3
65
10 700 Z3
53
9 400 M1
47
9 200 M2
46
4 400 M3
22
3 000*P1
15
*Transferred (0730) to
outdoor tanks
9.4
38 000 N1-3
190
34 200 N3-6
171
18 000 Z1
90
9 500 Z2
47
4 500 Z2-3
22
4 700 Z3
23
2 800 Z3
14
3 600 M1
18
2 600 M2
13
2 800 M3
14
No data available
7.4
33 000 N1-3
165
32 000 N3-6
160
22 500 Z1
112
13 500 Z2
67
10 000 Z2-3
50
7 400 Z3
37
6 200 Z3
31
6 100 M1
30
4 200 M2
21
7 400*M3
37
No data available
22.4
28 500 N1-3
142
29 500 N3-6
147
23 000 Z1
115
10 500 Z2
52
3 000 Z2-3
15
1 200 Z3
6
1 200 Z3-M1
6
1 100 M1
5
1 600 M2
8
1 200 M3
6
No data available
4.1
36 000 N1-3
180
32 000 N3-6
160
20 000 Z1
100
12 000 Z2
60
7 500 Z2-3
37
5 800 Z3
29
6 200 Z3
31
6 800 M1
34
5 400 M2
27
4 600 M3
23
No data available
12.8
Fig. 5 Growth and survival rats of P. monodon larvae on three different feeding regimes
in indoor tanks. Experiment B
Fig. 6 Histogram representing the phytoplankton community within the larval rearing tanks during Experiment B (each day is
sub-divided into a.m. and p.m. counts)
Note: Blank spaces indicate that no samples were taken on these days
Table 7 - Larval count and development et P. monodon larvae on four different feeding
regimes in outdoor tanks - Experiment C1/
Feeding option tested: cultured live food (C-I)
Total
Replicate I
Replicate II
Days after water Total
Larval
Total
Larval
hatching volume larval Larval density larval Larval density
stage
stage
(1)
count
(No./1) count
(No./I)
2
700
50 400 N3-6
72
58 800 N3-6
84
3
850
38 675 Z1
45
55 675 Z1
65
4
350
27 500 Z2
32
49 300 Z2
58
5
850
13 600 Z2-3
16
22 525 Z2-3
26
6
850
7
850
2 550 M2
3
1 700 M2
2
8
850
2 700 M3
3
1 700 M3
2
9
850
2 500
3
5 600
7
Survival rate (%)
5.0
9.5
Mean survival rate (%) 7.8
Feeding option tested: frozen Acetes (C-II)
2
700
56 700 N3-6
81
50 400 N3-6
72
3
850
61 200 Z1
72
64 600 Z1
76
4
850
44 200 Z2
52
56 100 Z2
66
5
850
14 475 Z2-3
17
10 200 Z2-3
12
6
850
7
850
11 050 M1
13
8 500 M1
10
8
850
10 200 M2
12
4 675 M2
5
9
850
5 000
6
5 000
6
Survival rate (I)
8.2
7.7
Mean survival rate (%)
10.3
Feeding option tested: dry Acetes (C-III)
2
700
50 400 N3-6
72
63 000 N3-6
90
3
850
55 675 Z1
65
55 675 Z1
65
4
850
42 200 Z2
50
49 300 Z2
58
5
850
33 575 Z2-3
39
27 950 Z2-3
27
6
850
7
850
17 000 M2
20
47 600 M1
56
8
850
35 275 M3
41
45 050 M2
53
9
850
10 000
12
35 000
41
Survival rate (%)
18.0
55.6
Mean survival rate (%)
40.6
Feeding option tested: Control - no feeding (C-IV)
2
700
51 800 N3-6
74
61 600 N3-6
88
3
850
38 250 Z1
45
63 775 Z1
51
4
850
38 200 Z2
45
19 500 Z2
23
5
850
36 550 Z2-3
43
23 375 Z2-3
27
6
850
7
850
2 550 M1
3
8
850
3 400 M2
4
9
850 Discarded
Discarded
Survival rare (%)
Mean survival rate (%)
Replicate III
Total
Larval
Larval
larval
density
stage
count
(No./I)
58 800 N3-6
84
55 675 Z1
65
51 000 Z2
60
5 525 Z2-3
6
5 100 M2
1 700 M3
5 200
8.8
51 100
67 150
55 000
6 800
N3-6
Z1
Z2
Z2-3
6
2
6
73
79
65
8
6 800 M1
6 375 M2
10 000
14.9
8
7
12
51 800
45 900
44 200
29 750
74
54
52
35
N3-6
Z1
Z2
Z2-3
35 700 M1
32 725 M2
25 000
48.3
42
38
29
54 600
32 300
17 850
41 225
78
38
21
46
N3-6
Z1
Z2
Z2-3
32 300 M1
9 350 M2
Discarded
38
11
Fig. 7 Survival rate of P. monodon larvae on four different feeding regimes in
outdoor tanks - Experiment C
4.4 Discussion
Although the studies of Hameed Ali and co-workers in India were restricted to the
development of a 'frozen' crustacean tissue suspension for larval feeding, the present
investigation would suggest that a 'dry' crustacean tissue preparation may hold even
greater potential as a larval shrimp feed. For example, in the two outdoor feeding trials
conducted (experiments A and C) the highest mean larval survival rate observed was for
the dry Acetes feeding option - 46.7% and 40.6% (calculated after 10 and 9 days from
hatching, respectively), followed by frozen Acetes - 29.4% and 12.7%, and cultured live
food - 24.7% and 9.5%. However, the performance of all three feeding strategies was
poor within the indoor rearing tanks (experiment B); highest mean survival rate being
recorded for the frozen Acetes feeding option - 12.7% (calculated after 10 days from
hatching), followed by cultured live food - 9.5% and dry Acetes - 8.2%. The poor larval
survival observed for the cultured live food feeding strategy was particularly surprising,
since survival rates of 30-40% from N to P1 are normally reported for this feeding
strategy in Leganes (Kungvankij et al., 1984).
Despite the high larval survival observed in outdoor rearing tanks with the dry
Acetes feeding regime, all Acetes treatments displayed reduced larval development and
growth compared with the cultured live food feeding strategy; larval development being
delayed by at least one day, with the exception of larvae fed dry Acetes during
experiment A. Furthermore, although no high-density phytoplankton blooms and crashes
were observed within the Acetes fed culture tanks during water management, the rearing
water of culture tanks receiving frozen Acetes was noticeably 'frothy’ and 'odorous' by
the last night feedingn (2400 h; or 1600 h after water management). However, apart
from the development of a heavy vibrio infection during experiment A in one of the
culture tanks receiving a fertilization/cultured live food feeding strategy, no further
bacterial outbreaks were observed. This was surprising, as one may have expected the
rapid development of a contaminating bacterial and fungal flora, particularly within the
frozen Acetes fed culture tanks.
During the present investigation the frozen Acetes feeding option performed as
well as the cultured live food feeding strategy on the basis of larval survival. Larval
survival was within the range reported by Alikunhi et al., (1980) for P. monodon using a
wet suspension - mean survival of 25.3% from N6 to P1 after seven culture runs.
5. ADVANTAGES AND DISADVANTAGES OF A CRUSTACEAN TISSUE
SUSPENSION FEEDING SYSTEM
5.1 Advantages
Compared with conventional live food feeding practices the development of a
successful suspension feeding system would offer numerous advantages to the shrimp
farmers:
(i)
It would involve the use of a single 'non-living' food item for the entire hatchery
culture cycle from N to P1.
(ii)
It is a simple feeding system which can be easily adopted by hatchery staff with
little training requirement; thus reducing the level of technical skill required to
operate a hatchery (from the live food production viewpoint).
(iii)
It would totally dispense with the use of sophisticated algal/diatom monoculture
rearing facilities and the use of live food organisms such as Brachionus spp. and
Artemia nauplii. At present the maintenance of live culture organisms constitutes
the major work load in hatcheries
(iv)
By eliminating the need for live food production systems, it would simplify
hatchery design and more importantly reduce the high ‘start-up’ capital cost
requirements for a shrimp hatchery; thus facilitating the development of 'smallscale' shrimp hatcheries by the family operator with limited resources. For
example, using a conventional live food feeding strategy, Kungvankij et al.,
(1984) estimate the capital investment and operational cost for a small-scale or
'backyard' shrimp hatchery in Southeast Asia to be not more than US$30 000
and US$ 10 000 respectively (hatchery production capacity of 1-5 million postlarvae per annum). At present at least 20% of the total larval rearing tank
capacity of small tank shrimp hatcheries (Satul system) is recommended for algal
production (Kungvankij, 1982).
(v)
It would involve the use of a locally available food item and at a cost below that of
conventional 'imported' food sources, such as Artemia cysts. In many developing
countries the importation of Artemia cysts necessitates import clearances, taxes
and the availability of foreign exchange facilities. By contrast, total sergestid
shrimp (Acetes) landings from capture fisheries in the Philippines for 1983 was
reported to be 26 217 metric tons (FAO, 1984). Although the fishery is seasonal
(depending on locality), pre-dried supplies can be purchased and stored until
required. The market cost of Acetes and a range of other food items commonly
used at Leganes is shown in Table 8. Although it was not Possible to calculate
the live food feeding costs per PL produced at Leganes the Centre
Océanologique de Bretagne (France) have estimated the dry weight cost of
producing Artemia nauplii and Brachionus spp. to be US$ 220/kg and US$ 2
000/kg respectively (Girin, 1979). The etimated dry Acetes cost for producing 1
million P1 larvae is P.Ps. 140 or P.Ps. 0.00014/P1. This calculation is based on a
larval survival rate of 40% from N to P1, and the use of 0.10 mg dry Acetes/larvae
at N3-6 and Z1, thereafter increasing the feeding rate by 20%/day until P1
(equivalent to the use of 3.5 kg of fry Acetes for an initial stocking of 2.5 million
N1 larvae). However, these costs do not include grinding and operating costs
such as labour. According to Hameed Ali, Dwivedi and Alikunhi (1982) the
operating costs of PL production using a wet crustacean feeding system are at
least half that of conventional live food production systems.
(vi)
The feeding system involves the use of a food item, the nutrient profile of which
approximates to the larval shrimp's own dietary requirement; in theory the best
food to feed a shrimp larvae is a shrimp larvae.
Table 8
Market Cost of Acetes and some Commonly Used Food Items-1/
Food Item
Fresh foods
Acetes ('Alamang')
Mussel (Perna spp.)
Squid
Trash fish (Tilapia spp.)
Trash fish (sardines)
Chicken egg
Dry food
Acetes
Artemia cysts
Market Cost
(P.Ps./kg)2
10
20(excluding shell)
25
2
15-17
1.75(per piece)
403
850 - 2 0005 (imported)
4
1
Source - Ms. K.G. Corre (March 1985)
2
Market costs at the time of this mission (March, 1985), P.Ps. 18 = US$ 1.00
3
All Acetes costs are exclusive of grinding
4
San Francisco Bay Brand
5
Saunders Brand (Great Salt Lake)
5.2 Disadvantages
(i)
There is a risk of disease transmission to the developing larvae when using
tissue suspensions prepared from closely related food organisms (e.g., 'Thelli',
M. dobsoni), It is essential therefore, that strict attention is paid to the preparation
and processing (boiling/drying) of the food organisms used.
(ii)
The Indian method of storing the prepared crustacean tissue suspension is
questioned. At present, appropriately sized feed particles are diluted by 300% by
weight with water and stored in a refrigerator for periods of up to 24 hours until
fed. The studies of Grabner et al., (1981; on the suitability of frozen and freezedried zooplankton (Artemia salina and Moina, spp.) as a feed for fish larvae have
shown that freezing causes considerable cell damage which results in extensive
leaching of water soluble nutrients on thawing into water. For example, these
researchers report that after 10 minutes at 9°C, about 70-75 percent of the
activities of proteases and L-lactate dehydrogenase, and an even larger
percentage of the free amino acids, have disappeared from the food material and
can be recovered in soluble form in the water. Not only would these soluble
nutrients act as a fertilizer for algal/diatom growth, but their loss from the
crustacean tissue suspension with time would lead to a progressive decrease in
the nutritive value of the feeding suspension to the developing larvae, It would be
more advantageous to directly freeze the appropriately sized feed particles and
to dispense the frozen material into a feed suspension during each individual
feeding interval. This would not only result in an enhancement of the nutritive
value of the feed suspension but it would also obviate the necessity to prepare
the feed suspension afresh on a daily basis. Alternatively, the feed material could
simply be dried and fed as such.
(iii)
The dependency of the 'wet' suspension feeding system on freezing/refrigeration
facilities necessitates a 'dependable’ power supply with adequate backup.
(iv)
Potential deleterious effect on water quality. particularly if uneaten food is
allowed to accumulate in the culture tank. Although these spoilage problems can
be avoided by keeping strict controls on water management, it may be necessary
to introduce antibiotics into the rearing water to check the development of
contaminating bacteria and fungi (Lewis et al., 1982; Simon, 1981)
(v)
Labour and equipment requirement for 'wet' sieving or 'dry' grinding.
(vi)
In view of the potential deterious effect of a crustacean tissue suspension on
water quality, the suspension feeding system may only be suited to small or
'manageable' hatchery rearing tanks of 1-2 ton capacity, where strict controls can
be made on water quality.
6. CONCLUSIONS
Despite the encouraging results obtained by Hameed Ali and co-workers in India,
and during the present NACA/SEAFDEC feeding trials with a 'wet' suspension feeding
strategy, it may be more profitable in the short term to concentrate research effort on the
refinement of a larval feeding system based on the use of a dry crustacean tissue
suspension. The results obtained during the present investigation clearly indicate that
the dry feed particles are consumed by the larvae and possess a nutritional quality
capable of sustaining larval growth and survival. However, at present it is not known the
contribution the 'background' natural phytoplankton community plays in the nutrition of
the developing larvae and in the apparent success of the crustacean tissue suspension
feeding strategy. Clearly, long-term feeding trials are required over a complete growing
season, and under a variety of climatic and hatchery conditions, before the true potential
of a crustacean suspension can be fully assessed. A list of suggested research topics is
given in Annex 1.
REFERENCES
Alikunhi, K.H., et al., Observations on mass rearing of penaeid and Macrobrachium
1980
larvae, at the Regional Shrimp Hatchery, Azhicode, during 1979 and 1980.
Bull.Dept.Fish,Kerala, 2(1):68 p.
1982
, Report on mass rearing of shrimp larvae at the Regional Shrimp
Hatchery, Azhicode, during 1981. Bull.Dept.Fish.Kerala, 3(1):40 p.
CRC, CRC Handbook of Mariculture, Volume 1 - Crustacean Aquaculture, edited by
1983
J.P. McVey, CRC Press Inc., Boca Raton, Florida, 442 p.
FAO, Yearbook of fishery statistics, 1983. Yearb.Fish,Stat.,(56):393 p.
1984
(trilingual)
Girin, M., Some solutions to the problem of producing juvenile marine finfishes
1979
for aquaculture. European Mariculture Society, Special Publication No. 4,
pp. 199-209
Grabner, M., W. Wieser and R. Lackner, The suitability of frozen and freeze-dried
1981
zooplankton as food for fish larvae: A biochemical test program.
Aquaculture, 26:85-94
Hameed Ali, K., A new system for mass rearing of penaeid shrimp larvae.
1980
Proceedings of the first National Symposium on Prawn Farming, Bombay,
16-18 August, 1978; 254-62
Hameed Ali, K. and S.N. Dwivedi, Acceleration of prawn growth by cauterisation
1977
of eye stalks and using Acetes indicus as supplementary feed.
J.Ind.Fish.Assoc.Bombay, 3-4 (1-2):136-38
Hameed Ali, K., S.N. Dwivedi and K.H. Alikunhi, A new hatchery system for
1982
commercial rearing of penaeid prawn larvae. Bull.Central Inst.Fish.
Education, Bombay, 2-3:9 p.
Jones, D.A., Penaeid larval culture using microencapsulated diets. Paper
1984
presented at the First International Conference on the Culture of Penaeid
Prawns/Shrimps, Iloilo City, Philippines, December 4-7, 1984
Kanazawa, A., Penaeid nutrition. In Proceedings of the Second International
1983
Conference on Aquaculture Nutrition; Biochemical and Physiological
Approaches to Shellfish Nutrition, edited by C.D. Pruder, C.J. Langdon and
D.E. Conklin. Baton Rouge, Louislana State University Press, pp. 87-105
Kungvankij, P., The design and operation of shrimp hatcheries in Thailand.
1982
In Working Party on small-scale shrimp/prawn hatcheries in South east
Asia, Semarang, Central Java, Indonesia, 16-21 November 1981, II.
Technical Report, SCSFD & C.P., Manila, Philippines, May 1982. pp. 11720
Kungvankij, P., et al., Shrimp hatchery design, operation and management.
1984
NACA Training Manual Series No. I, November 1984, in press
Lewis, D.H., J.K. Leong and C. Mock, Aggregation of penaeid shrimp larvae due
1982
to microbial epibionts. Aquaculture, 27:149-55
Liao, I., A brief review on the larval rearing techniques of penaeid prawns.
1984
Paper presented at the first International Conference on the Culture of
Penaeid Prawns/Shrimps, Iloilo City, Philippines, December 4-7, 1984, in
press
New, M.B., A review of dietary studies with shrimp and prawns
1976
Aquaculture, 9:101-44
Scura, E.D., J. Fischer and M.P. Yunker, The use of microencapsulated feeds
1984
to replace live food organisms in shrimp hatcheries. Paper presented at the
First International Conference on the Culture of Penaeid Prawns/Shrimps,
Iloilo City, Philippines, December 4-7, 1984
Simon, C.M., Design and operation of a large-scale, commercial penaeid shrimp
1981
hatchery. J.World Maricult.Soc., 12(2):322-34
Watanabe, T., C. Kitajima and S. Fujita, Nutritional value of live food
1983
organisms used in Japan for mass propogation of fish: A review.
Aquaculture, 34:115-43
ANNEX
SUGGESTIONS FOR FUTURE RESEARCH
Ideally the following trials should be conducted in replicate 1-2 t hatchery rearing
tanks using initial nauplii concentrations of 100-150/1. Nauplii should be obtained from
individual spawners, and more than one species tested. For example, depending on
location: P. monodon, P. indicus, P. merguiensis, P. semisulcatus, P. japonicus, P.
aztecus, P. duorarum, P. setiferus and P. vannamei.
A.
RESEARCH PROPOSALS INVOLVING THE EXISTING DRY ACETES
FEEDING STRATEGY
1.
Acetes feed survey
2.
(a)
Existing fishery - size, current use of Acetes, fishery forecasts
(b)
Market availability - geographical and seasonal basis; cost depending on
form available (fresh/dry)
Acetes feed quality
(a)
3.
Nutrient content
(i)
proximate composition - moisture, protein, lipid, ash, crude fibre
(ii)
amino acid, fatty acid, mineral and possibly vitamin composition
(iii)
contaminants/anti-nutritional factors - pesticide residues, heavy
metals, thiaminase activity
(iv)
spoilage characteristics/shelf life - lipid oxidation, microbial spoilage
(c)
Seasonal variation in nutrient content
(d)
Stability in water - rate of nutrient loss depending on feed particle size and
period in water
Role of natural phytoplankton in the nutrition of Acetes-fed larvae
Using standard hatchery procedures the following observations should be made
in conjunction with larval growth and survival:
(a)
Phytoplankton species composition and population density in culture tank
with larvae receiving normal crustacean tissue feed Input
(b)
Phytoplankton species composition and population density in culture tank
containing no shrimp larvae but receiving normal feed input
(c)
Phytoplankton species composition and population density in culture tank
containing no shrimp larvae and receiving no feed input
(d)
Phytoplankton species composition and population density in culture tank
containing shrimp larvae bur: receiving no feed input
(e)
Effect of lighting (indoor/outdoor tanks, covered or uncovered) on the above
(f)
Effect of water exchange (% tank volume/day) on the above
(g)
Effect of different crustacean tissue preparations on the above
(h)
Effect of different feed levels and feed particle sizes on the above
2.
Feed preparation and formulation
(a)
Drying technique.
Effect of different drying techniques on feed performance; air drying
(indoors/outdoors), freeze-drying or drum drying.
(b)
Vitamin/lipid fortification.
The effect of adding a vitamin/lipid supplement to the dry Acetes prior to
feeding should be tested. The aim of using such a supplement is to fortify
Acetes with essential vitamins and polyunsaturated fatty acids, to make the
particles more visible to the larvae (by using carophyll red as a pigment),
and to increase the water stability of the feed particles and so reduce
nutrient leaching (by emulsification with soy lecithin). Such a diet could also
be tested during the nursery stage as a replacement for Artemia nauplii. A
suggested vitamin/lipid supplement for testing could be as follows:
Carophyll red1
Soy lecithin
Shrimp head oil2
Vitamin mix3
0.5 g
1.5 g
5.0 g
2.0 g
1
10% suspension of canthaxanthin in an oil base
2
If not available, can be replaced with red fish oil or krill oil
3
To supply/kg finished diet: vitamin A, 6 500 IU; vitamin D3, 2 000 IU, vitamin E, 300 mg; menadione
sodium bisulphite, 12 mg; thiamine mononitrate, 35 mg; riboflavin, 50 mg; D-calcium pantothenate,
150 mg; biotin, 0.5 mg; folic acid, 7.5 mg; vitamin B12, 0.05 mg; niacin, 220 mg; pyridoxine HCL, 30
mg; ascorbic acid, 2 000 mg; choline chloride, 1 000 mg; myo-inositol, 2 000 mg; antioxidant, 125
mg
The vitamin/oil premix should be prepared by first dissolving the carophyll red
and soy lecithin in the fish or shrimp oil, followed by the vitamin premix. Mix and
homogenize well and then apply to the dry basal protein source (i.e., Acetes; using 9 g
of vitamin/oil premix for every 91 g of dry pre-ground Acetes). When using shrimp or fish
oil, efforts should be made to procure sources which have been pre-stabilized with 250500 ppm antioxidant.
3.
Suitability of other crustacean preparations for larval feeding
Depending on availability, these could include M. affinis, M. dobsoni, P. stylifera,
N. tenipes, O. nepa and Mesopodopsis spp.
When monitoring larval growth and survival, the following additional data should
be collected (if possible):
(a)
Feeding incidence of the larval population (presence of food particles in the
gut or faecal strands)
(b)
Behaviour of the feed particles in water - buoyancy, dispersion properties
(c)
Incidence of larval deformities
(d)
Information on water quality - oxygen, pH, ammonia, phosphate, nitrate,
nitrite, salinity
(e)
Bacterial/fungal contamination of rearing water
(f)
Development of micro-flora on crustacean feed particles in water
4.
Comparative larval feeding trials with other existing hatchery feeding regimes
These feeding trials should be compared on the basis of larval growth and
survival, dependability and cost/unit of production.
B RESEARCH PROPOSALS INVOLVING MODIFICATIONS TO THE DRY ACETES
FEEDING STRATEGY
1.
Feeding regime
(a) To determine the optimum feed particle size for each larval stage.
Present feed particle size
N3-6 - Z2
50<125
Z3 - M2
125<250
M3 - P1
250<350
Suggested size ranges for testing
10 - 200
100 - 500
200 - 600
(b) To determine the optimum feeding level for each larval stage.
Present feeding level is 0.10 mg/larvae/day at N3-6 and Z1 , thereafter
increasing by 20%/day until P1. Feeding levels of 0.05, 0.10, 0.15, and 0.20
mg/larvae/day, and subsequent daily increments of 10, 15, 20, 25 and 30%
should be tested. For example, the delayed larval development observed for
Acetes fed larvae may have been due to under feeding.
(c) To determine the optimum frequency of feed presentation.
Present feeding frequency is four feeds/day at 0830, 1200, 1700 and 2400 h.
In view of the potential loss of soluble nutrients through leaching, the effect of
a range of different feeding frequencies should be tested. For large-scale
hatchery operations the feasibility of using automatic feed delivery systems
should also be tested.
III. ANNEXES
ANNEX 1
FRY PRODUCTION IN HATCHERIES
PROGRAMME
10 February 1986
–
Arrival of participants at ROVINJ
–
Presentation of the MIRNA Station
Mr. Z. FILIC
11 February 1986
–
Brood-stock : Collection - Transport - Stocking
Mr. Z. FILIC
–
Natural and induced reproduction : The different functions of hormones
Mr. L. COLOMBO
12 February 1986
–
Laboratory : Equipment - Catheter - Dissection - Hypophysation –
Injection Egg observation
–
Phyto and zooplankton cultures
Mr. G. FANCIULLI
13 February 1986
–
Artemia cultures
Mr. SORGELOOS
–
Other micro-organisms employed in aquaculture - Natural zooplankton
yield
Mr. A. PONTICELLI
14 February_1986
–
Influence of ambient, factors on larvae rearing
Ms BARAHONA FERNANDEZ..
–
larvae rearing and prefattening of sea-bass and gilthead sea-bream
Mr,. J. M. RICARD
Mr. G. ARCARESE
15 February 1986
–
Filtration and recirculation
Mr. J. PETIT
16 February 1986
–
Visit to ISTRIE
17 February 1986
–
Visit to the MIRNA facilities
18 February 1986
–
Site - Dimensioning - Productive Programme
Mr. L. BERG
–
Structures - Equipment - Economic aspects
Mr. G. BRUNEL
–
Use of thermic discharges
Mr. P. BRONZI
–
Larvae rearing and prefattening of mullets
Mr. C. NASH
19 February 1986
–
Larvae rearing of crustacean
Mr. F. LUMARE
Mr. de la POMELIE
–
Larvae rearing, of mollusc
Mr. G. ROMAN CABELLO
Mr. J. P. FLASSCH
20 February 1986
–
Larvae rearing and prefattening of Tilapia
Mr. C. AGIUS
–
Larvae rearing and prefattening of other fish
Mr. B. MENU
MR. C. KITAJIMA
–
Controlled spawning : effect of temperature and light
Mr. M. DEVAUCHELLE
–
General review and economic aspects of fry production
Mr. G. RAVAGNAN
21 February 1986
–
Transfert to ZADAR
–
Presentation of CENMAR
Mr. D. LISAC
–
Presentation and visit of hatchery
Mr. D. LISAC
–
Hatchery recirculation system
Mr. D. LUZAVEC
22 February 1986
–
Live food production presentation
Ms V. FRANICEVIC
–
Reproduction strategies in CENMAR
Ms G. SARUSIC
24 February 1986
–
Live food production practice and discussion
Ms M. CRNICA
Ms V. FRANICEVIC
–
Larval rearing presentation
Mr Z. VEJMELKA
–
Hatchery auxiliary equipment
Mr. D. LUZAVEC
25 February 1986
–
Larval rearing practice and discussion
Mr. Z. VEJMELKA
Ms. J . BUBLE
–
Fry rearing presentation
Mr. Z . VEJMELKA
–
Fish nutrition
Mr. A. TACON
26 February 1986
–
Visit to CENMAR cage culture facility
Mr. L. MILJAC, I. IVOS, J. MAURIN
27 February 1986
–
Fry rearing practice and discussion
Mr Z. VEJMELKA
Mr D. LISAC
–
Hatchery production and development strategies
Mr D. LISAC
–
Prophylactic measures
Ms G. SARUSIC
28 February 1986
–
Round table of participants and CENMAR staff
–
Departure
ANNEX II
TRAINING SESSION - YUGOSLAVIA
LIST OF PARTICIPANTS
Name
Mr. Carmelo AGIUS
Occupation
Lecturer
Country
MALTA
Mr. Carmelo GALEA
Mr. Selim DINGER
Ms. Agathi KENTRU
Ms. Maria Teresa DINIS
Technician (lab.)
Biologist
Biologist
Biologist
MALTA
TURKEY
GREECE
PORTUGAL
Mr. Serge CORNEILLIE
Biologist
BELGIUM
Mr. George L. GEORGIOU
Mr. Andreas LAGGIS
Mr. Savas J. AGROTIS
Mr. Bechir BRINI
Mr. Djeffel BELKACEM
Mr. Ali EL OUAER
Ms, Maria Helena
BARAHONA FERNANDEZ
Biologist (mariculture) CYPRUS
Aquaculturist
GREECE
Managing Director
CYPRUS
Ingénieur
TUNISIA
Directeur/Ingenieur ALGERIA
Ingénieur
TUNISIA
Professor/Researcher PORTUGAL
administration
Mr. Pedro POUSAO
FERREIRA
Ms. Gordana SARUSIC
Mr. Adel SOUISSI
Mr. Issam KROUMA
Biologist
PORTUGAL
Ichtiopatologist
Etudiant
Head of Division of
animal production
aquaculturist
Biologist
Biologist
Agricultural Engineer
YUGOSLAVIA
TUNISIA
SYRIA
Mr. Damir MUSIN
Mr. N. JASPRICA
Mr. DUZGUNES
YUGOSLAVIA
YUGOSLAVIA
TURKEY
Adress
8A , Main Street, DINGLI, Malta - Present adress : Faculty of science. Kingston
Polytechnic, KINGSTON UPON THAMIS, Surrey - U.K
Biology Department, University of Malta; Tal - Qroqq, Msida, MALTA
Fisheries Department - Bodrum - MUGGA - Turkey
Fisheries Department - PREVEZA - Greece
Instituto Nacional de Investigas das Pescas, Av. Brasilia 1 400 LISBOA Portugal
Zoological Institute, Laboratorium for Ecology, Naamsestraat 59, 3 000 LEUVEN - Belgium
Fisheries Department, NICOSIA - Cyprus
Aquaculture Center of Achelloos S.A., 30001, Neochori - Nessolonghio
Sagro Aquaculture Ltd, P.O. Box 19, PAPHOS, Cyprus
Centre national d'Aquaculture, Route de Khniss - 5 000 - MONASTIR
Unité aquacole de Mazafran - DOUAOUDA MARINE (v. TIPASA) Algeria
Centre National d'Aquaculture, Route de Khniss, 5 000, MONASTIR - TU
Instituto Nacional de Investigacao das Pescas, Av. Brasilia, 1400 LISBOA or
Departamento de Biologia, Faculdade de ciencias, r. Escola Politecnica, 1200
- LISBOA - Portugal
Instituto Nacional de Investigacao das Pescas, Av. 5 de Outubro 8 700 OLHAO - Portugal
CENMAR - 57 232 - NIN - Yugoslavia
7, Rue Habib et Ferhi, 1 009 - EL OUARDIA - TUNIS - Tunisia
Ministry of Agriculture and Agrarian Reform - DAMASCUS - Syria
Biological Institute - DUBROVNIK - Yugoslavia
Biological Institute - DUBROVNIK - Yugoslavia
Tarim Opmanve Koyisieri Bakanligi - ANKARA . M. MUDURUGU – ANKARATurkey
ANNEX III
TRAINING SESSION – YUGOSLAVIA
LIST OF LECTURERS
NAME
Mr. Z. FILIC
ADRESS
MIRNA - 52 210 - ROVINJ - Yugoslavia
Mr L. COLOMBO
Istituto di Endocrinologia Comparata
Via Loredan 10 - 75 100 PADOVA - Italy
Tel.049/831 720
Via L. Bozzo 12/14
16 032 - CAMOGLI (GE) Italy
Tel.0784/864 100
Artemia. Reference Center, State University,
Rosier 44, B. 9 000 GHENT - Belgium
E.N.E.A. Strada Provinciale Anguillarese
00 100 - ROME - Italy
Instituto Nacional de Investigacao das
Pescas
LISBOA - Portugal
IFREMER - Station de PALAVAS –
Tel.067/68 083
MONTPELLIER
Tlx 490 419
France
I.N.R.A. Campus de Beaulieu
Tel.99/631 888
35 042 - RENNES - France
Tlx 730 866
S.T.M. Via Durer 38
Tel.049/617 171
35 100 - PADOVA - Italy
SEPIA - 2, rue Stephenson
Tel.13/0439927
78 181 - St. QUENTIN - Yvelines Cedex Tlx 699 734
France
ENEL - CRTN - Via Rubattino 54
20 134 - MILAN0 - Italy
Tlx 310 496
ADCP/FAO - Via delle Terme di Caracalla Tel.06/57976470
00 159 - ROME - Italy
Tlx 610 181
CNR - Via Franca Creta
LESINA (Foggia) Italy
IFREMER - Station de PALAVAS
Tel.67/68 083
MONTPELLTER - France
Tlx 490 419
Instituto Espanol de Oceanografia
tel.981/205 362
Laboratorio de la CORUNA, Apt. 130
Tlx 86 070
15 080 - LA CORUNA - Spain
IFREMER - B.P. 337
TeL.98/458 055
29 273 - BREST Cedex - France
Tlx 940 627
Faculty of Science - Kingston Polytechnic, Tel.01/549 1366
KINGSTON UPON THAMIS - SUrrey - U.K.
SODAB
Tel.96/923591
- TREGUIER - France
Shimabara Branch Station of NAGASAKI
Pref. Institution of Fisheries - JAPAN
IFREMER - B.P. 337
Tel.98/458 055
29 273 - BREST Cedex - France
Tlx 940 627
ADCP/FAO
Tel. 6/57976465
Via delle Terme di Caracalla
00 159 - ROME - Italy
CENMAR
57 000 - ZADAR - Yugoslavia
Tel.057/24 994
Mr. G. FANCIULLI
Mr. P.SORGELOOS
Mr. A.PONTICELLI
Ms M.H. BARAHONA
FERNANDEZ
Mr. J.M. RICARD
Mr. J. PETIT
Mr. L. BERG
Mr. G. BRUNEL
Mr. P. BRONZI
Mr. C. NASH
Mr C. LUMARE
Mr Ch. de la POMELIE
Mr. G. ROMAN
CABELLO
Mr. J.P. FLASSCH
Mr. C. AGIUS
Mr. B. MENU
Mr. C. KIbTAJIMA
Ms N. DEVAUCHELLE
Mr. A. TACON
Mr. D. LISAC
Ms G. SARUSIC
Tel:052/811 111
Tlx 25 242
Ms V. FRANICEVIC
Ms M. CRNICA
Ms J. BUBLE
Mr. Z.VEJMELKA
Mr. D. LUZAVEC
Mr. L. MILJAC
Mr. I. IVOS
Mr. J. MAURIN
57 232 - NIN - Yugoslavia
Tel.057/64 332
Tlx 27 248