COMMUNICATIONS (Continue)

NUTRITIONAL MANAGEMENT IN HATCHERY LARVAL NUTRITION OF MARINE FISH AND SHRIMP (Continue)

LITERATURE

BECK, A.D.-LGENGTSON, D.A.- 1982 International Study on Artemia XXII. Nutrition in an aquatic toxicology - diet quality of geographical strains of Artemi: pp. 161–169. In: Aquatic Toxicology and Hazart Assessment. 5th Conf. ASTM STP 766. Pearson, J.G.- Foster, R.B. - Bishop W.E. (Eds). Amer. Soc. Testing and Materials, Philadelphia, USA, 400 p.

BENIJTS, F.-VANVOORDEN, E.- SORGELOOS, P.-1976 Changes in the biochemical composition of the early larval stages of the brine shrimp, Artemia salina L.: pp. 1–9. In: Proc. 10th European Symposium on Marine Biology. Vol. 1. Research in mariculture at laboratory and pilot scale. Persoone, G.- Jaspers, E. (Eds). Universa Press, Wetteren Belgium : 620 p.

BENGTSON, D.A.- LÉGER, PH.-SORGELOOS, P.- 1991 Use of Artemia as a food source for aquaculture, pp. 255–285. In: Artemia Biology, BROWNe, R.A. - SORGELOOS, P.- TROTMAN, C.N.A. (Eds). CRC Press, Boca Raton, Florida, U.S.A.: 374p.

CHAMBERLAIN, G.-1988 Coastal Aquaculture, 5(1).

COUTTEAU, P.- LAVENS P.- SORGELOOS, P.- 1990 The use of yeast as single-cell protein in aquacultural diets. Med. Fac. Landbouww. Rijksuniv. Gent, 54 (4b), 1989

DEPAUW, N.-PRUDER, G.-1986 Use and production of micro-algae as food in aquaculture: practices, problems and research needs : pp. 77–106. In : Realism in Aquaculture: Achievements, Constrains, Perspectives. Bilio.-Rosenthal, H.-Sinderman, C.J. (Eds)-European Aquaculture Society - Bredene - Belgium : 585 p.

DEVERESSE. B.- ROMDHANE, M.- BUSSI, M. RASOWO, J. LÉGER, PH.-BROWN, J.-SORGELOOS, P.-1990 Improved larviculture outpu8ts in the giant freshwater prawn Macrobrachium rosenbergii fed a diet of Artemia enriched with (n-3)-HUFA and phospholipids. World Aquaculture,21(2):123–125

FAO - 1989 Planning for Aquaculture Development. ADCP/REP/89/33, FAO, Rome, Italy, 68 pp.

FRANICEVIC, V.-LISAC, D.-BUBLE, J.- LÉGER, PH.- SORGELOOS, P.- 1987 Etude internationale sur l'Artemia. XLII. L'effet de la qualité nutritionnelle de l'Artemia sur la croissance et la survie des larves du loup Dicentrarchus labrax L. dans une écloserie commerciale : 139–145. In: Production in Marine Hatcheries. Lois, B. 'Ed), FAO-MEDRAP, Roving-Zadar-Yugoslavia - 387 p.

FRENTZOS, TH.-SWEETMAN, J.- 1989 an integrated marine fish farm in Cephalonia-Greece : 143–153
In: A Biotechnology in Progress. Dc PAUW, N.-JASPERS, E.-ACKEFORS, H. and WILKINS, N. (Eds). European Aquaculture Society - Bredene - Belgium : 593 p.

FUKUSHO, K., - 1989 Biology and mass production of the rotifer Brachionus plicatilis. Int. J. Aq. Fish. Technol. 1 : pp. 232–240

JONES, D.A.- KANAZAWA, A.- ONO, K.- 1979 Studies on the nutritional requirements of the larval stages of Penaeus japonicus using microencapsulated diets. Mar. Biol. 54 : pp. 261–267

JONES A.- HOUDE, E.D.- 1981 Mass rearing of fish fry for aquaculture : pp. 351–374
In : Realism in Aquaculture : Achievements, Constraints, Respectives. Bilio, M.-Rosenthal, H. and Sinderman G.J. (Eds). European Aquaculture Society - Bredene-Belgium : 585 p.

KANAZAWA, A.- TESHIMA, S.- SASADA, H.- 1982 Culture of prawn larvae with microparticulate diets, Bull.Jap.Soc.Sc.Fish. 48(2) : PP. 195–199

KOMIS, A.-NAESSENS, B.- VAN BALLAER, E.- VAN SPRANG, P. SORGELOOS; PHP, 1989 New developments in the mass culture and nutritional enrichment of the rotifer Brachionus plicatilis using artificial diets : p. 306 - European Aquaculture Society, Special Publication № 10 - Bredene - Belgium : 344 p.

LANGDON, C.J.- WELDOCK, M.J.- 1981 The effect of algal and artificial diets on the growth and fatty acid composition of Crassostra gigas spat, J. Mar, biol. Assoc. U.K. 61 : pp. 431–448

LÉGER PH.- BENGTSON, D.A.- SIMPSON, K.L. - SORGELOOS, P.- 1986 The use and nutritional value of Artemia as a food source. Oceanogr. Mar. Biol. Ann. Rev., 24 : pp. 521–623

LÉGER, PH.- BENGTSON, D.A.- SORGELOOS, P.-SIMPSON, K.L.- BECK, A.D.- 1987a The nutritional value of Artemia: a review pp. 357–372 In: Artemia Research and its Applications - Vol. 3. Sorgeloos, P.-Bengtson, D.A.-Cedleir, W.-Jaspers, E.(Eds). Universal Press - Wetteren - Belgium : 556p.

LÉGER, PH.- BIEBER, G.E.- SORGELOOS, P.- 1985a International Study on Artemia, XXXIII-Promising results in larval rearing of Penaeus stylirostris using a prepared diet as algal substitute and for Artemia enrichment. J. World Aquacul. Soc. 16 : pp. 354–367

Léger, PH.- CHAMORRO, R.- SORGELOOS, P.- 1987b Improved hatchery production of postlarval Penaeus vannamei through application of innovative feeding strategies with an algal substitute and enriched Artemia. Paper presented at the 18th Ann. Meeting of the WAS, Guayaquil (Ecuador) - January 12–23, 1987.

LÉGER, PH.-DHONT, H.-VAN SPRANG, P.- SORGELOOS, P.- 1991 Live feed for halibut larvae. Rotifer Culture and enrichment. Artemia production and enrichment. Halibut Project NTNF-FINA. Final Report Phase I-SINTEF Aquaculture Department-Trondheim-Norway - in press?

LÉGER, PH.-GRYMONPRÉ D.-VAN BALLAER, E.- SORGELOOS, P.- 1989 Advances in the enrichment of rotifers and Artemia as food sources in marine larviculture pp. 141–142. In ÷ Aquaculture Europe 1989. Short Communications. Abstracts. European Aquaculture Society - Special Publication № 10 - Bredene-Belgium: 344 p.

LÉGER, PH.- NAESSENS-FOUCQUAERT, E.-SORGELOOS, P.- 1987c International Study on Artemia. XXXV. Techniques to manipulate the fatty acid profile in Artemia nauplii and the effect on its nutritional effectiveness for the marine crustacean Mysidopsis bahia (M.): pp. 411–424. In : Artemia Research and its Applications - Vol. 3-SORGELOOS, P.-BNGSTON, D.A.- DECLEIR, W.- JASPERS, E. (Eds)- Universa Press - Wetteren-Belgium : 556 p.

LÉGER PH.- SORGELOOS, P.- MILLAMENA, O.M.- SIMPSON, K.L.- 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:pp. 71–82

LÉGER PH.- SORGELOOS, P.- 1991 Optimized feeding regimes in shrimp hatcheries. In: Culture of Marine Shrimp : Principles and Practices - FAST, A.W.- LESTER, L.J. (Eds) - Elsevier, in press

LÉGER, PII.- VANHAECKE, P.-SORGELOOS, P.-1983 International Study on Artemia. XXIV. Cold storage of live Artemia nauplii from various geographical sources: Potentials and limits in aquaculture-Aquacultutre Eng., 2: pp. 69–78

O'LEE, D.- 1989 Why Ecuador is among world leaders in shrimp garming. Fish Farmin International, April 1989 - Cultivated micro-algae as a source of omega-3 fatty acids: 51–56
In : Fish, Fats and your Health, Proceedings of the International Conference on Fish Lipids and their Influence on Human Health - Svanoy Foundation - Svanoybukt - Norways : 73 p.

RILMMER, M.A.-REED, A.- 1990 Effects of nutritional enhancement of live foodorganisms on growth and survivla of Barranmundi/Seabass Lates calcarifer (Bloch) larvae. Advances in Tropical Aquaculture, Thiti, Feb. 20 - March 4, 1989 - AQUACOP - IFREMER-Actes de Colloque, 9:pp. 611–623

ROMDHANE, M.S.-DEVRESSE, B.- LÉGER, PII.- SORGELOOS, P.- 1991 Effects of feeding nutritionally enriched Artemia during a progressively increasing period on the larviculture of the freshwater prawn Macrobrachium rosenbergii.-J. World Aquac. Soc., in press

SORTGELOOS, P.- 1980 The use of the brine shrimp Artemia in aquaculture: pp. 25–46 In : the brine shrimp Artemia - Vol.3 - Ecology, Culturing, Use in Aquaculture-PERSOONE, G.- SORGELOOS, P.-ROELS, O.- JASPERS, E. (Eds)- Universa Press-Wetteren-Belgium : 456 p. Sorgeloos, P.- 1989 Stress resistance in postlarval penaeid shrimp. Artemia Newsletter, 12:
12–13

SORGELOOS, P.-LÉGER, PH.- LAVENS, P.- TACKAERT, W.- VERSICHELE, D.- 1986 Manual for the culture and use of brine shrimp Artemia in aquaculture Artemia reference Center, State University of Ghent, Belgium:319 p.

SORGELOOS, O.-LÉGER, PH.- 1991 Improved larviculture outputs of marine fish, shrimp and prawn
J. World. Aquac.Soc., in press

SORGELOOS, P.-LÉGER, PH.- LAVENS, P.- 1988 Improved larval rearing of European and Asian seabass, seabream, mahi-mahi, siganid and milkfish using enrichment diets for Brachionus and Artemia
Word Aquaculture, 19(4) : pp. 78–79

SORGELOOS, P,-LÉGER, PH - LAVENS, P. - TACKAERT, W. - 1987 Increased yields of marine fish and shrimp production through application of innovative techniques with Artemia. Aquaculture et Développement, Cahiers Ethologie Appliquée, 7 : 43–50

SORGELOOS, P - VAN STAPPEN, G. - 1991 New shrimp diets from Artemia System. New larval diets from San Francisco Bay Brand, Inc. Larviculture & Artemia Newsletter, 19: pp. 26–27, 42–43

SPURRIER, W.- 1988 The white book of shrimp (original in Spanixh, English version by Maria Eugenia de Boeing)
Chamber of Shrimp Producers, Guayaquil, Ecuador

TACKAERT, W.-ABELIN, P. DHERT, PH.- SORGELOOS, P.-1989 Stress resistance in postlarval penaeid shrimp reared under different feeding procedures
J. World Aquac. Soc., 20(1):P. 74A

TAYLOR, A.- 1990 A double bonus for shrimp farmers. Fish Farming International File, 4(2)

VAN BALLAER, E.- AMAT, F.- HONTORIA, F.- LÉGER, PH.- SORGELOOS, P.- 1985 Preliminary results on the nutritional evaluation of w3-HUFA enriched Artemia, nauplii for the larvae of the seabass, Dicentrarchus labrax
Aquaculture, 49:pp. 223–229

VANHAECKE, P.-SORGELOOS, P.- 1980 International Study on Artemia. IV. The biometrics of Artemia strains from different geographical origin : pp. 393–405
In : The Brine Shrimp Artemia - Vol. 3 - Ecology, Culturing, Use in Aquaculture PERSOONE, G.- SORGELOOS, P.- ROELS, O.- JASPERS, E, (Eds) - Universa Press, Wetteren, Belgium : 456p.

WALKER, K.F.- 1981 A synopsis of ecological information on the saline lake rotifer Brachionus plicatilis (Müller, 1786) - Hydrobiologia, 81/82: pp. 159–167

WATANABE, T.- KITAJIMA, C.- FUJITA, S.- 1983 Nutritional values of live food organisms used in Japan for the mass propagation of fish : a review - Aquaculture, 34:115–143

PLANNING, DIMENSIONING & MAINTENANCE CRITERIA FOR SEA WATER HATCHERY BUILDING AND EQUIPMENT

By Mr. Alessandro MORETTI
PADOVA - ITALY

INTRODUCTION

This work originates from specific design criteria, sizing indexes and construction specifications widely adopted by S.T.M. when implementing several hatcheries in past years.

Each subject has evidently been summarized from the original treatment presented elsewhere and therefore implies a redder possessing an established bio-technological background on the matter.

Tot. Volume of water expressed in liter per second.

Tot. pressure head or Tot. static head expressed in meters as the sum of:

Difference in meters between Seawater surface and sea water outlet of the pump. PLUS Losses of charge due to pipeline PLUS Losses of charge due to equipment on the line.

Design material: Cast iron

Very heavy
Good for use with seawater
Low consumption and very efficient
Large amount of water with low charge
Open channel impeller

Design material: Aluminum

Light and easy to handle
Use in seawater only if epoxy painted
High consumption
Max. of flexibility, good charge and large amount of water
High speed centrifugal impeller

Fig. 7 Magnification of a plyurethane single call

U. V. STERILIZER

VIEW AND TECHNICAL INFORMATION OF UV STERILIZER

Figure 8 - View and technical information of UV sterilizer

Figure 9 - Titanium stainless steel plat exchangers

S1 : hot seawater outlet
S2 : fresh water outlets, to the boiler
S3 : cold seawater inlet
S4 : freshwater inlet, from the boiler

Suitable stainless steels for saltwater use in treat exchangers: titanium steel and molibdenum steel (Avesta 250 SMO)

Maintenance. Disassemble plates only when the head loss is very high and/or the expected cannot be maintained. Clean plate surface with from water and soft brush. Organic matter can be removed by a 2% NaNOH solution at 50°c. NaNo3 solution destroys calcium deposits. Wash thoroughly and riassemble. Substitute washers if necessary.

1- GENERAL CRITERIA FOR ARCHITECTURAL DESIGN

One of major factors determining the correct sizing of a hatchery is the simple computation of the total amount of fry to be produced. However, this number gives only an indication, to be related with the following general principles for planning and dimensioning a large scale hatchery unit :

1.1- Hatchery management criteria

The strategy of production can easily determinate hatcheries varying in size and number of sectors. The most important criteria in hatchery management are:

• Use of seedlings.

  According to distinct production targets the fry reared could be use

  1. to stock a fattening facility, through 2–4 outputs per year from November to June;

  2. to be marketed entirely to various farms, through 4–6 outputs all year round;

  3. to stock a brackishwater lagoon, through maximum 2 outputs per year, from March to June.

This leads to three distinct hatchery management's and returns on investment.

• Eggs production.

  Egg quality directly influences production : larvae and juveniles out of naturally spawned eggs can reach a double survival rate and better growing performances than those obtained from delayed spawning. Hormone-induced eggs can vary in quality being adopted HCG rather than LH-RH.

• Adopted technology standards.

  A high-technology can significantly reduce total surfaces and volume needed in comparison with a low-technology plant. High-technology infact means high intensification of rearing techniques and high production rate per unit volume.

• Multispecific or monospecific hatchery.

  A hatchery involved in the reproduction of various species can better return on the investment costs through a longer production season based on several natural species-specific ovodeposition periods (it is the case of a sequence of sea bream, sea bass and red sea bream). Diversification helps to lower biological and marketing risks.

Notwithstanding is very dangerous and impractical to generalize and give standard formula about the hatchery design, an example if suitable management criteria is outlined below.

A one-million-fry facility engaged in multispecific production. High-technology with high production ratio (No. of fry/unit of volume) in semiclosed recycling circuits. Rearing parameters under close control and fully adjustable. Maximum flexibility. Egg produced only hrough either natural or LH-RH-induced spawning. Two months closing during summertime for cleaning, disinfection and maintenance.

1.2- Architectural philosophy

The construction of a hatchery is related with sizing criteria and with choices aiming to an easy management and low maintenance and running costs. Among the most important criteria to be respected are the following :

• Proper production flow chart

  The internal organization of an hatchery must follow and optimize the functional relationships among the various steps of production :

  1. exchange of algae, rotifers and artemia among rearing sectors.

  2. larvae, fry and breeders transfer/grading,

  3. sectors under special light regimes.

• Temperature gradients among sectors

  To respect the optimal temperature ranges in separate rearing sectors bears a better use of energy, saving heat wastes.

• Widely dimensioned operative area

  A proper balance must be chosen between needed surface, future increase of production and investment costs. Each compartment must be easily accessible, with suitable free areas where comfortably operate routine rearing activities: cleaning, disinfection, maintenance, prophylaxis, etc…

• Correct geographic exposition of different units.

  In order to cut running costs, mainly fuel for heating and electric current for light it is convenient to arrange the various sectors in a way to utilize :

  -   direct sunlight exposition for algae mass culture.

  -   pre-fattening under a greenhouse.

• Future extension forecast.

  A correct, foreseeing design can allow a subsequent hatchery enlargement at a fairly reduced cost in comparison with the investment coasts of the first plant.

1.3- Engineering philosophy

Engineering aspects are very important in order to keep the work safe using reliable technology and materials which must be:

1. specially suited for use in sea water environment,

2. non toxic to fish (eggs, fry and adults),

3. easily worked with and maintenanced,

4. highly resistant to repeated cleaning using strong chemicals.

1.4- Logistic elements

Planning a hatchery is strictly related to the site:
direct relationship of employed technology with the country general technological level.

Careful attention must be paid to integrate hatchery design and construction with some aspects of site location as overall technical level of the country, staff formation level, local availability of services and spare parts of equipment and after sale assistance and routine maintenance.

For an hatchery planned following the above described criteria the relation among the different inside units are done in Figure 1.

2- DIMENSIONING OF PRODUCTION SECTORS AND PRODUCTION SERVICES

The most important sectors and items to be dimensioned are:

• Breeding,

• Larval rearing,

• Weaning,

• Live food production

• Water piping

• Pumping station

• Mechanical filtration

• Biological filtration

• UV water sterilization

• Alarms

• Seawater & air heating

• Electrical network

• Generator set

2.1- Breeding

Broodstock is usually kept under semi-natural condition in outdoor facilities such as small earth ponds or enclosures. Indoor facilities must be stocked with en entire lot of breeders needed for a rearing cycle, some time (1–3 months) before spawning time. Conditioning to optical spawning include control of water temperature, photoperiod and feeding regime.

The breeding unit includes: rearing tanks, piping system, pumps, heating system, lighting system and air system.

Tanks

Concrete or fiberglass tanks, round or square in shape, capacity 10–20 m³. Screened bottom drainage with valve.

Water circuits

An open circuit
Non-toxic PVC glued pipes. Easy disassemblable for cleaning purposes.

Heating

Titanium steel plate exchanger equipped with a 3-way driven by a thermostat, accuracy ± 1°C.
High/low temperature alarm system.

Lighting

65W fluorescent lamps per tank.

Air supply

At least 4 aeration points per tank through PVC transparent open-end pipe.

Sizing

One must consider:

Oversizing is current practice and a specific «production index» of 10.000 fry per kg of breeder is recommendable.

2.2. Larval rearing

It is the area where to incubate fertilized eggs and subsequently rear hatched larvae up to partial metamorphosis, and includes: rearing tanks, piping, biofilter, recirculating pumps, UV lamps sterilizer, heating, and air supply. See an example in Figure 2 and 3.

Tanks

Fiberglass cylindro-conical tanks, capacity 3–5 m³. Bottom drainage with valve, lateral screened outlet.

Water circuits

1. Semiclosed recycling circuit with biofilter and recirculating pumps.
2. Make-up pipeline to partially renew the recirculating water.
   Non-toxic PVC glued pipes. Easy disassemblable for cleaning purposes.

Biofilter

Type : downflow with airlifts.
Medium : open cell atoxic polyurethane foam.
Tank : fiberglass or concrete rectangular tank equipped with bottom drainage.
A mechanical prefilter to remove feaces, excess rotifers and artemia is recommended.

Recirculating pumps

Two pumps per circuit, of which one is in stand-by
Material: polypropylene or other atoxic plastic materials.
Floating switch with out of order alarm.

UV lamp sterilizer

Lamps: high pressure mercury-vapor lamps.
Irradiation chamber: polypropylene.
UV intensity meter, water alarm and time recommended.

Water heating

Titanium steel plate exchanger equipped with a 3-way valve driven by a thermostat, accuracy ± 1°C.
High/low temperature alarm system.

Lighting

150W halogen lamps with timer and trimmer to create a dawn effect during switching on and off. It allows to adapt intensity and photoperiod to various fish species.

Air Supply

Central tank aeration through PVC transparent pipe and fine air stone, close to the bottom outlet. It maintains larvae and their live food in gentle suspension.

Sizing

One must consider:

1. total needed production per cycle: number of 45-days larvae reared in the same time;
2. average starting density: number of freshly hatched larvae per m³;
3. average survival rate per cycle: 15% seabream and red drum; 30% seabass.

2.3. Weaning unit

This sector receives partially-metamorphosed larvae and provide to its complete weaning. It is composed by: rearing tanks, piping, biofilter, recirculation pumps, UV lamp sterilizer, heating, lighting and air supply. See an example in Figure 4.

Tanks

Concrete or fiberglass tanks, rectangular or square in shape, capacity 6–10 m³. Bottom drainage with valve, lateral screened outlet.

Water circuits

1. Semiclosed circuit with biofilter and recirculating pumps.
2. Make-up circuit to partially renew the recirculating water.
3. c- Open circuit to supply water on a flow-through basis.
   Non-toxic PVC glued pipes. Easy disassemblable for cleaning purposes.

Biofilter

Type: clownflow with airlifts.
Medium: open cell atoxic polyurethane foam.
Tank: concrete of fiberglass rectangular tank equipped with bottom drainage.

Recirculating pumps

Two pumps per circuit, one in stand-by.
Material: Polypropylene or other atoxic plastic materials.
Floating switch with out of order alarm.

UV lamp sterilizer

Lamps: high pressure mercury vapor lamps.
Irradiation chamber: polypropylene.
UV intensity meter, water alarm and timer recommended.

Water heating

Titanium steel plate exchanger equipped with a 3-way value driven by a thermostat, accuracy ± 1°c
High/low temperature alarm system.

Lighting system

116W fluorescent lamps per tank.

Air supply

At least 2 aeration points per tank : PVC transparent pipe coarse air stones.

Sizing

One must consider :

2.4- Live food production unit

Algae and rotifers are first cultured in an air-con room under sterile conditions in a liquid medium up to volumes of 5–10 liters. Afterwards the inoculate are transferred in a larger air-con room and cultured in bigger containers - usually hanging polyethilene bags from 50 to 400 liters. Artemia are made hatch in separated facilities under controlled environmental factors and used as freshly hatched nauplii or 1 to 2 days metanauplii.

The live food production unit includes : phyto-zooplankton pure culture sector; phytoplankton massive culture sector; rotifer massive culture sector and artemia massive culture sector.

Phyto-zooplankton pure culture sector

A room with shelves under 24 hours illumination and air + CO₂ supply hosts the pure strains of algae and rotifers up to a culture volume of 6–10 liters. Holding facilities are represented by Pyrex ® glass containers ranging in size from test tube to Erlenmayer flask to round flask. Lab glassware, fertilizers, chemicals, microscopes, kits for water analysis, etc… complete the equipment of his sector. The water supply requires a filtering system able to remove particles down to 1 μm (absolute) and a well dimensioned UV light sterilizing device to assure a supply of sterile water. Ambiance temperature is 18–20°c, assured by an air conditioner.

Phytoplankton massive production sector

A room with a strong 24 hours light supply and larger volumes is devoted to the culture of large quantities of algae and intermediate inoculate of rotifers. Holding facilities are represented by hanging transparent polythylene 150 l bags transparent polyethylene 400 l bags kept standing by a wire cylinder. The air system is provided with a CO₂ supply. The ambiance temperature is as above. Water temperatures between 18 and 22°C are reached by a titanium steel plate exchanger equipped with a 3-way valve driven by a thermostat, accuracy ± 1°c.

Rotifer massive production sector

Rotifers are usually produced in cylindro-conical fiberglass 1–3 m³ tanks with strong aeration from the bottom and high water temperatures (24–27°c), usually achieved by electrical heaters or ambience thermoregulation. Light is requested only for normal working operations (collection, cleaning, etc…). Water treatment and being heating as above.

Artemia massive production sector

Artemia nauplii are produced in cylindro-conical fiberglass 1–3 m³ tanks with a white inner surface and a transparent window close to the bottom drainage. Nauplii are concentrated at the bottom through positive phototaxis at the window. A very strong aeration from the bottom and high water temperatures (25–28°c, achieved as for rotifers) are requested. A strong light illumination (2 × 58W neon day-light per tank) is requested at least during the first hours of incubation.

Sizing

For a total output of one million fry, the following indexes are considered:

2.5- Water piping system

Pipelines carrying seawater must be of atoxic solvent welding PVC, having low frictional losses and being highly resistant to corrosion and repeted cleaning. Threaded fittings should be limited where quick and repeted disassembling is imperative.

Water being carried under pressure, pipes must be properly moored to avoid dangerous vibrations and possible effects of water hammer. Pipes are usually placed above the tanks and equipment, at a height of + 3.00m from the floor level. Wall angle supports, pillars and roofed chains are used for mooring.

Relatively long pipeline tracts, from 10 to 40m, must be easily disassemblable by means of fast rubber joints, socket unions, flanges or others. This allows easy cleaning procedure (disinfection, fouling removal).

Sizing

2.6 Pumping station

The pumping station of the hatchery requires a minimum of 3 pumps per circuit, each with a capacity (Qp) equal to 1/2 of the maximum needed flow (Qmax)

Qp = Qmax/2

In this way, during the maximum use, the pumps will never work more than 16 hours per day (2 working and 1 in stand-by).

Selection among centrifugal pumps

1. In general such pumps are well suited for a wide range of flows and heads :

   -   surface pumps : horizontal axis; efficiency : 65 to 70% good but a starting (priming) device is necessary;

   -   submersible pumps : vertical axis; efficiency : 65 to 80% the best solution considering flow, head and efficiency.

2. Reliability

   Submersible pumps are better than surface pumps due to :

   -   accuracy requested for assembling and installation to satisfy the difficult condition of functioning;

   -   proper water-tightness as the pumps are working into the water.

3. Maintenance

   Maintenance and reparation, considering work and spare part cost, are similar. It is necessary to take the submersible pumps out of the station once a year : a lifting device is needed.

Sizing

The initial decisions required in outdoor pump selection require the knowledge of the following factors:

1. total head,

2. total flow,

3. characteristics of seawater pumped : rough, filtered or other,

4. continuous or intermittent service,

5. pump material ; aluminum pump : lighter and easier to carry of lift; low resistance to corrosion when permanently installed; cast iron pump : heavier; suitable for permanent installation; must be protected from corrosion by surface epoxy painting and combination of a stainless steel or bronze impeller; sacrificial zinc anodes are dangerous because of the toxicity or their corrosion products. See the example in Figure 6.

2.7- Mechanical filtration

Mechanical filtration is intended to condition seawater to match various exigences related to each hatchery sector. It is done by removing undesired solid particles and organisms as water is screened while passing through various porous materials.

The filter selection is done by considering the following characteristies of each device:

2.8-Biological filtration

Water flowing in larval rearing and weaning sectors is treated by passing through a biofilter, usually a coarse porous substratum submerged in a separate container whose large relative surfaces are colonized by nitrifying bacteria. Such microorganisms are able to convert highly toxic ammonia to comparatively non toxic nitrites. Excessive accumulation of these chemicals is practically mastered by replacing recycled water with fresh «un-polluted» seawater (semi-closed recycling systems).

The most reliable system is a down-flow biofilter where water enters from above, flows through the substratum and then is recollected at a lower level and pumped back to rearing tanks, after Being heated and sterilized.

Nitrifying efficiency is dependent on several factors:

1. total water flow,

2. total filter surface, absolute and relative,

3. residence time (contact between water and surface),

4. dissolved oxygen and ph (temperature and salinity being seldom variable),

5. generation of metabolic wastes : total biomass, feed characteristics and feedin practices.

A magnification of a single polyurethane cells is shown in figure 7.

2.9- UV water sterilization system

The concentration of potentially hazardous microorganisms as bacteria, viruses and parasitic protozoa can be controlled in the culture environment by means of UV radiation without affecting fish.

UV light characteristics Figure 8

The most effective UV radiation has a wavelength of 265 mm, called UV-C.

UV lamp power is expressed in mJ/cm² (1 mJ = 1mW/s). If the lamp output is 10 mW/cm² and the residence time of water inside the sterilization chamber is 3 seconds, then the UV-C supplied is 30 mJ/cm². Generally speaking an output of 40 mJ/cm² at the end of the UV lamp life is considered worth.

UV light intensity is directly linked to the transparency of water to UV rays, called the transmission factor. This parameter should be determined to allow proper dimensioning and calibration of the sterilizer.

In the hatchery recirculating systems the transmission factor generally ranges from 0,80 to 0,90.

UV lamp equipment

Ultraviolet light in the UV-C band is emitted by mercury vapor lamps. High pressure lamps are fairly more efficient and productive than low pressure lamps. Lamps are usually installed inside an irradiating chamber made either by stainless steel AISI 316 or polypropylene and equipped with a control module. It hosts a % UV meter to indicate UV intensity, UV alarm of low intensity, a temperature meter to indicate presence of water and an hour counter to record UV lamp life.

Selecting a UV light sterilizer

Main parameters to be considered for appropriate dimensioning of sterilizers:

-   requested level of UV-C irradiation, usually 10 mJ/cm²;

-   species of microorganisms to remove;

-   transmission factor of the water (measured by photometer);

-   maximum water flow.

The last two parameters are quoted in the choosing tables supplied by the manufacturers.

Caution

UV light is harmful to unprotected eyes and bare skin.

2.10- Seawater and air heating system

Two boilers are normally installed in a single room of the hatchery. These two boilers are calculated in order to serve 100% of total needs each.

The pipe starting from the boiler room serves two different lines:

-   heat exchangers for seawater heating (Figure 9),

-   air heaters.

Temperature of boiler water has to be maintained at 50–60°C in order to avoid as much as possible salt deposits inside the plate exchangers.

Temperatures are automatically regulated by means of an electronic thermostat, directly related to a 3- way valve. A thermometer installed on the main PVC pipe acts as an upper and lower limit temperature alarm probe.

2.11- Alarm systems

The main sectors which need an alarm system are:

Pumping station

Acoustic default alarm on each pump.
Minimum level acoustic alarm for all the system, stopping the pumps.

Larval rearing unit

Acoustic default alarm on each pump.
Minimum level acoustic alarm for all the system, stopping the pumps.
Temperature alarm set at ± 0,5°C the working temperature.
Dissolved oxygen alarm, starting an acoustic alarm.

Weaning unit

Minimum water level acoustic alarm for the system, stopping the pumps.
Temperature alarm at ± 1°C the working temperature.
Dissolved oxygen alarm, starting an acoustic alarm and opening a modular valve for automatic oxygen supply in the recirculating water.

Boilers room

An acoustic alarm on each pump for heating system.
An acoustic alarm on each boiler in case of boilers failure.

All these alarms should be connected to a synoptic alarm board placed in the hatchery office.

2.12. Electrical system

Main input

All the individual units are supplied by the plant Low Voltage (380/220) network, deriving from an eventual distribution control panel being connected to the sector Central Control Board by means of a 3 phase and neutral line.

Control and distribution panels

Immediately beyond the delivery point, an omnipolar general and sectioning adapter must be placed of differential magnetothermic type. It should be regulated for time and threshold of intervention.

All outgoing lines must be protected by magnetothermic switches and, individually or in compatible groups, by a differential cutoff adapter in a way that any earth blowout does not affect the whole plant.

Conductors must only be connected by means of terminals inside the panel and not along tubes or canals. All the lines must be clearly identified when they leave the panel as far as their final destination (boxes, connector blocs, lamps, canals, sockets).
Materials: IP55 fiberglass reinforced polyester.

Lamps and sockets

Lamps must be metal or other non-inflammable material (self-extinguishing resin). Suitable protection must be chosen for development of high temperatures. Minimal protection IP55.

Sockets are bipolar and reversible with earth wire, round plug holes, nominal voltage 220V/10A (light sockets) and 16A (MP sockets). They must be protected from accidental contact with voltage bearing parts also when plug is inserted and pulled out.

Earthing system

A general earthing circuit is absolutely necessary, usually including:

-   underground embedded earth plates interconnected by copper wire,

-   earth conductors,

-   safety conductor network

To such circuit the following items are connected:

-   sockets earth poles, lights and MP,

-   unipotential circuit between water intakes and discharge pipes,

-   all metal parts of equipment and supporting structures.

2.13- Generator set

An automatic device to supply electrical energy in case of black out is absolutely necessary for an aquaculture plant. Usually this is achieved by setting one generator capable of cover the needs of the whole farm.

The power set in k VA is calculated on the installed power of the farm, given space to 10– 15% excess power.

When the hatchery has a capacity of 2 millions fry/year it is advisable to install one generator especially for it provided with an automatic start when the main power supply fails.

In the electrical connection design one must take into account the difference of electrical input when each engine starts, that is 4 to 6 time higher than the normal running input. Delay switches must be introduced to avoid that all the equipment start together. Some devices have no vital importance and could remain unconnected to the generator.

The generator must always be ready to start automatically (10 to 20 min. working/week).

3- MAIN HATCHERY MAINTENANCE AND CLEANING OPERATONS

More and more relevant appears the importance of cleaning and maintenance routines in an industrial scale hatchery. The summer period as period of complete interruption for production activities grants the optimization of hatchery operational efficiency in terms of staff turnover, radical signification of rearing facilities and proper equipment maintenance.

Daily maintenance and cleaning routines

Glassware cleaning.
Phyto-zooplancton unit equipment cleaning and disinfection.
Larval rearing and weaning screened-outlets disinfection.
Larval rearing and weaning tank bottom cleaning.
Floor disinfection.
Bag and cartridge filters cleaning and disinfection.
UV quartz sleeve cleaning.
Sand filter backwash.

Weekly maintenance and cleaning routines

U.V. quartz sleeve and radiation meter cleaning
Boiler turnover.
Heating pumps turnover.
Air-blowers filter control.
Phyto-zooplancton seawater supply cleaning and disinfection.
Rotifers seawater supply cleaning and disinfection
Artemia seawater supply cleaning and disinfection.
Sea water pumps turnover.
Rotary filters cleaning and disinfections.
Air compressor (if present) drain water purge.

Monthly maintenance and cleaning routines

PVC pipe cleaning and disinfection (biofaouling removal).
Heating exchanger cleaning.
Sand filter disinfection.

Yearly maintenance and cleaning routines

Submersible pumps cleaning, washer, oil substitution.
Pipes general cleaning and strong disinfection.
U.V. lamps control.
Other pumps and engines control and maintenance.
Metallic parts repainting.
Air-blowers disassembling and checking.
Sand filters disassembling and sand cleaning or replacing.
Biofilter cleaning and disinfection.

Figure 1 - Regulations among hatchery sectors

Figure 2- Sketch of a larval rearing tank and outlet arrangement

Figure 3 - View of the recirculating system for larval rearing.

Figure 4- View of on-line equipment in weaning recirculating system.

Figure 5- Abacus for computation of head loss and pipe diameters.

Management of Clams Hatchery

By Mr. Jean-Pierre BAUD
FRANCE

The only dependable way today to produce spat molluscs for aquaculture is to use hatchery facilities. This is valid both for extensive and intensive on-growing, up to the market size.

Many species of clams have been fished all over the world, but only three of them are commonly reared; the Manila clam, Rutidapes philippinarum, the European clam, Ruditapes decussatus and the hard clam Mercenaria mercenaria. As Aquaculture of the Manila clam has largely developed in European waters during the last decade, our subject will focus on this species, which has a great ecological tolerance, and exhibit a fast growth during most of the rearing stages.

Molluscs hatcheries usually sell spat from 2 to 4 mm in length. The basic techniques were developed by Loosanoff and Davis (1963) and by Walne (1966). These may be used for many species including oysters, clams and scallops. However not all of them are so easy to produce : on France, it is generally considered that the Manila clam is the most easy species to work with.

High levels of production in reliable conditions may be achieved when the following requirements are fulfilled : water quality and processing, sanitary care prevention of Molluscs illness and their adequate treatments.

LOCATION OF AN HATCHERY

Siting for an hatchery is essential

Oceanic waters are required for larval rearing. They should be characterized by a low turbidity and a high quality. Micropollutants, hydrocarbons and heavy metals are highly toxic for the larvae of molluscs.

Estuarine waters, with high levels of particulate matters and phytoplankton are more adequate for the older spats.

Water processing

Water storage should be very short before its use within the hatchery. All materials used for rearing facilities such tanks, pipes, pumps and taps should be chemically inerts. Heavy metals are toxic, even in very low concentrations. Plastic materials should be preferred.

Water filtration

A primary filtration should be made under pressure, in a sand filter (20–50μm), for the water irrigating genitors and spat. Another filtration on stacks (1–5μm) is required for the larval rearing and the culture of microalgaes.

Heating

Water is usually warned (between 18–25°c) according to the species, thanks to a Titanium heat-exchanger. The hot water may be produced from a boiler. The temperature of the tanks dedicated to the larval rearing should be kept constant, eventually by a climatizing the room.

HATCHERY CONCEPT

Four units have to be considered :

• broodstock conditioning and spawning area;

• room of larval rearing;

• micronursery;

• room for algal production.

Conditioning the genitors aims at obtaining the reproduction for a longer period than in the field. For that, healthy reproductors, 2 and 3 years old, are kept in warm water (20–25°c). They are fed ad libitum with phytoplactonic algae, at concentrations ranking from 1 to 10 thanks to an air-lift or on pulp, if the micronursery is watered from a pond or natural sea-water. In all cases, the algal density should be within 50–100 cells/microliter in the tank containing the meshes. The later rearing stages are generally performed in open environment, at ambient temperature.

FOOD PRODUCTION

Today, this production results in the main from fresh phytoplanktonic populations reared for that purpose. One may consider that the achievement of an hatchery largely relies on the quality and the quantity of the algae it may produce.

The implementation of the required quantities of algae takes place in two stages.

• Small and medium size volumes

  They are obtained in a closed room, maintained at 18–20°c and lightened with 3 000 to 10000 luxes. Filtered sea water (1 mm) is enriched with a culture medium (Conway, Provasoli…) including nutrients, vitamins, and traces of the required metals. The volumes of the successive jars are commonly of 15 ml, 500ml and 2 liters. All the solutions should be sterilized in an autoclave, before their inoculation with an axenic strain of algae.

• Larges volumes

  They are conducted in climatized rooms (20–25°c) with artificial light, or in greenhouse. The air supply, enriched with 1 % Co2, allows to maintain the pH between 7 and 8. The culture in large volume can be performed by sequential blooming. Cylindrical tanks of 800 - 400 1 and even 1 m³, are then used and filled every 4 days. The culture is distributed during the exponential growth. It is easy to develop, but reliability may not be satisfactory. Another type is the semi-continuous culture. A third of the volume in culture (jar of 20 l, plastic bag of 50–100 l, or Perspex cylinder of 200–300 l) is sampled every day, and a corresponding amount of fertilized sea water is added.

SPAWING

The best way to obtain spawning is a thermal shock in clean filtered sea water. After keeping them out of water for 2–3 hours, the genitors are successively immersed at 26°c for 1 hours, then at 20°C for 1 hour and so on. At the early beginning of the gametes release, the genitors are sorted according to their sex.

FECUNDATION

Higher rates of fecundation are usually obtained 1 hour after spawning a few milliliters of sperm are added to the required quantity of ovocytes, so as to obtain an adequate ratio between spermatozoids and ovocytes. A ration higher then 10 may lead to polyspermy. These controls need a microscope determination.

LARVAL REARING

The duration of this stage depends upon: the temperature, the salinity, the amount and the nutritional quality of food, the eggs physiological status, the water quality and the sanitary control.

Larval rearing usually lasts for 12 to 15 days, et 23°c. It is best performed into cylindrical tanks, with a conical bottom containing 400 liters of l ωm filtered sea water. A gentle bubbling is required. The water is renewed every two days. The larval density is kept at 12.5 larvae/ml at the beginning, and should reach 4 larvae/ml by the end of the larval rearing.

MICRONURSERY

It is the place where metamorphosis occurs, when the larvae are competent, and where the spats will be reared up to a size of 1–2 mm. Pediveliger larvae are therefore transferred into tabular meshes, at a density of 2 × 10⁶/m². A water current irrigates then from top to bottom, needs good technical knowledge to be run on the long term. The last way to produce algae is the chemostat. A continuous amount of fertilized sea water will replace into the tank, the quantity of algae given to the molluscs. Tuning such technique for several weeks or months requires technical achievements and a wide background.

SANITARY REQUIREMENTS

It is mandatory that hygiene and meticulous cleanliness are reinforce into a successful hatchery Several rules should be observed without exceptions:

• before use, all materials and tools should be cleaned with filtered sea water;

• after use, these should be carefully washed with an adequate detersive, and allow to dry in an oven:

• all building should be perfectly cleaned up, regularly;

• a sanitary break should be observed 1 month every year, during which every production should be stopped and the whole facility cleaned up.

During production, preventive treatments with hypochlorite, or curative with antibiotics may be used to stop bacterial development on shells of the spats, or at the last period of larval rearing. However, antibiotic use should be refrained in order to avoid the emergence of resistant strains of pathogens.

POTENTIAL USES OF SUBTERRANEAN SALT WATER FOR AQUACULTURE ON THE COAST OF «PAYS DE LA LOIRE» (FRANCE)

BAUR, J-P (1), ROBERT? J.M. (2), AND LE MOINE, O. (3) -(1) IFREMER-URRA. 85230 BOUIN, (2) Uiversité de Nantes, 2 rue de la Houssinière, 44072 Nantes, (3) Station Aquative, GIE, 59, 85330 Noirmoutien en l'Île (France).

INTENSIVE REARING OF THE MANILA CLAM (RUDITAPES PHILIPPINARUM) IN PONDS.

BAUD, J.P. et Haure J. FREMER, laboratoire régional de conchyliculture, Polder des Champs F-85230 BOUIN - FRANCE

MAROST EXPERIENCE IN SHELLFISH HATCHERY

By Mr. Jamel KASMI
MOROCCO

1- RÉSUMÉ

La création d'une écloserie mollusques au sein de la société Marost en 1985 avec des annexes de production d'algues a contribué en la réalisation d'une lignée la plus complète puisqu'elle possède les différentes étapes de production depuis la ponte jusqu'à la commercialisation.

Le choix de Marost s'est posé sur deux espèces : l'huître plate Ostrea edulis et la palourde Tapes decussatus, en se basant sur le fait de leur haute valeur commerciale et al présence de facteurs permettant leur élevage dans des meilleures conditions. La diversification dans ce domaine est marquée par l'introduction d'une troisième espèce : l'huître creuse Crassostrea gigas dont le but est d'alimenter les pares ostréicoles se trouvant sur la partie Ouest du Maroc Atlantique en matière de naissains.

2- INTRODUCTION

Suite aux études réalisées par I O.N.P., l' L.s.P.M. et al F.A.O. sur les espèces abritées par la lagune de Nador, il s'est révélé que celle-ci est propice pour l'élevage de certaines espèces de coquillages telles que Ostrea edulis et Tapes decussatus. De là il a été décidé la création du premier projet de développement de l'aquaculture au Maroc.

L'ostréiculture a débuté par un captage naturel sur des collecteurs : les chapeaux chinois et, en 1985, la création de la première écloserie mollusques fonctionnant pour les deux espèces et, en 1991, l'introduction de la gigas.

3- DESCRIPTION DE L'ÉCLOSERIE

Un schéma général de l'écloserie est représenté en Figure l. L'unité de production phytoplanctonique est formée trois salles équipées de matériel nécessaire, un petit laboratoire pour le stockage des produits chimiques et une petite salle pour le repiquage des souches, La tuyauterie arrivant dans ces salles passe à travers des filtres à sables, filtres à cartouches ultraviolets, filtres à chaussettes. A l'extérieur du bâtiment un local de CO₂. Les structures propres à l'élevage de coquillages sont formées par : une salle de conditionnement des géniteurs avec 10 bacs de 1 m3, une salle d'élevage larvaire avec 4 bacs de 15 m3, une unité de fixation dont une partie se trouve dans la salle larvaire fonctionnant en système semi-ouvert, une autre avec 10 bacs de 1 m3.

4- FONCTIONEMENT

L'écloserie mollusques à Marost fonctionne 8 à 9 mois par an aussi bien pour les huîtres que pour les palourdes, avec un cycle avancé s'étalant de janvier à avril; un cycle naturel de avril à septembre. Le naissain sortant mesure 1 à 2 mm.

4.1- Les algues

L'intéeêt essentiel des cultures des espèces phytoplanctoniques marines à Marost réside dans le fait de vouloir répondre aux exigences alimentaires des espèces élevées en reproduction contrôlée.

Les algues sont cultivées de façon intensive selon la méthode connue dite «discontinue» (utilisation totale des cultures); le système de production est basé sur le repiquage avec augmentation de volume. Les installations de culture sont conçues de manière à fournir les conditions favorables au développement de toutes les espèces utilisées et à permettre le contrôle des principaux paramètres écologiques.

Parmi les espèces utilisées:

• diatomees Chaetoceros calcitrans et gracilis
  Skeletonema costatum

• flagelees Isochrysis galbana
  Tetraselmis suecica

La technique utilisée pour les cultures monospécifiques reste une technique classique avec:

• des souches de conservation en tubes à essai 60 ml maintenir les différentes espèces cultivées à l'état pur et non contaminé;

• des souches de production dans des erlenmeyers 250 ml constituent le départ effectif de la production.

  Les repiquages de ces cultures souches se font selon un programme correspondant à leurs besoins spécifiques d'entretien et de production. Les premières sont repiquées une fois tons les 15 jours; les seconds une fois par semaine.

Les manipulations d'inoculation s'effectuent dans des conditions hygiéniques permettant de garder les cultures souches autant que possible à monospécifique et stérile:

• ballons de 20 litres permettent le développement de l'inoculum provenant des souches de manière suffisante pour pouvoir inoculer d'autres volumes plus grands, soit les 200 litres. Chaque ballon est inoculé par un erlenmayer de 250 ml;

• bacs 200 litres, ce sont les bacs de production de nourriture. Ils sont inoculés chacun par un ballon 20 litres et prennent en général 5 à 7 jours pour attendre les concentrations d'utilisation :

  -   Isochrysis 6.000.000 cellules par ml

  -   Tetraselmis 1.500.000 cellules par ml

  -   Skeletonema 4.000.000 cellules par ml

  -   Chaetoceros 5.000.000 cellules par ml

  Cette production est destinée aux géniteurs; larves; naissains.

4.2- Production naissains

4.2.a- Géniteurs

IIs proviennent soit de la pêche dans la lagune, soit directement de la production de Marost pour l'huître plate et la palourde, et. pour l'huître creuse, des pares ostréicoles sur l'Atlantique du Maroc.

Cycle avancé

II est basé sur le conditionnement des géniteurs introduits généralement en janvier jusqu'à avril en jouant sur deux facteurs : la température, augmentée progressivement de 13 à 22°c la nourriture donnée quotidiennement sous forme de mélange de diatomées et de flagellées à raison de 40 litres par bac de 1000 litres à une concentration moyenne de 3.000.000 cellules par ml.

La densité par bac étant de 150 pièces d'huîtres, 1000 pièces de palourdes.

La maturation arrive pendant un mois pour l'huître plate, 1,5 à 2 mois pour l'huître creuse et la palourde.

Cycle naturel

II s'étale d'avril à septembre. Les géniteurs matures dans la lagune donnent 2 à 3 jours après leur introduction des pontes pendant une période de 15 jours et sont remis à la lagune pour réintroduire d'autre. Pour l'huître creuse, les géniteurs qui ont pondu sont mis de côté.

4.2.b- Ponte/c

Chez la plate, il y a é mission des larves véligers «D» de taille 150 microns, alors que chez la palourde t la creuse, la pont est provoquée par choc thermique avec élévation de la température de 5 à 28°C et addition de sperme de quelques individus sacrifiés.

La fécondation, ainsi que le développement, se font dans le bac géniteur et ce n'est qu'après 24 heures que les larves trochophores sont transférées dans la bac larvaire.

4.2.c- Élevage larvaire

Il s'effectue dans les bacs de 15 m³ équipé chacun d'une lampe à sodium, trois résistances thermostatiques commandées pas microprocesseurs ainsi qu'une aération. L'eau pompée dans la lagune traverse des filtres à sable à une filtration de 50 microns puis dans des filtres à cartouches de 1 , 5 ou 25 microns et, en fin du système, des filtres à chaussettes de 1 ou 25 microns.

L'élevage larvaire dure 13 jours en moyenne pour la plate et 150/120 à 300/240 microns dans le cas de Ostrea, contre 110/90 à 240/300 microns pour la creuse. Il dure 8 jours pour la palourde avec passage de 110/90 à 200/150 microns. Les courbes de croissance des trois espèces sont représentées en Figure 2.

Le traitement des larves s'effectue de la même façon pour les trois espèces, avec un renouvellement total chaque deux jours, accompagné d'un tamisage dans des tamis de '50—85—100—150—180—200—220 microns et d'un comptage. Les larves ne présentant pas une bonne croissance sont éliminées.

La densité dans ces conditions ne dépasse pas 0.6 larves par ml avec un taux de survie moyen de 40 %.

La nourriture est apportée quotidiennement sous forme de mélange d'algues monocellulaires composée de flagellées et de diatomées dans les proportions suivantes:

-   70 % diatomées skeletonema + chaetoceros

-   30 % flagellées tetraselmis + Isochrysis.

La concentration finale dans le bac varie entre 20.000 à 30.000 cellules/ml. Au bout du treizième jour pour Ostrea et pour Crassostrea, huit jours pour Tapes, la larve développe un pied : c'est le stage «pied» et, lorsque l'examen au microscope montre un pourcentage de 70% de ce stade, on passe à la fixation.

4.2.d- Fixation

Elle est permanente pour les huîtres et temporaire pour les palourdes. Dans le premier cas, plusieurs substrats ont été utilisés, tel que les collecteurs en plastique : chapeaux chinois-des mailles carrées de 8 cm de côté sous forme de broche-, enfin, le broyât des coquilles d'huîtres, calibré entre 2 tamis de maille 350 et 220 microns. C'est ce dernier type qui est retenu actuellement.

Dans le cas des palourdes, la fixation se fait directement sur le tamis reposant dans un bac de 1 m³ avec une charge de 1,000.000 de larves. L'eau est renouvelée chaque jour tout en ajoutant 20 litres d'un mélange d'algues par bac à une concentration de 4.000.000 cellules/ml et une aération continue.

Un triage régulier tous les cinq jours est indispensable afin de séparer les tailles et d'éliminer le naissain de faible croissance.

4.2.e- Nurseries

Une fois le naissain reste sur le tamis 500 microns. il passe dans une pré-nurseries composée de quatre raceways, alimentée par un bassin de 40 m³, chargé de nourriture et dont la concentration finale est de 20.000 cellules/ml.

Le triage se fait chaque dix jours et la taille 2 mm est obtenue vers le 45^ème jour pour Ostrea et Crassostrea, et vers le 70^éme jour pour Tapes. Cette taille étant suffisante pour transférer le naissain en mer.

5- CONCLUSION ET RÉSULTATS

Le coquillage reste un produit de luxe dans le domaine de l'aquaculture, la maîtrise de la reproduction est une base pour développer d'autres espèces.

La tableau № 3 montre les différentes étapes pour produire une quantité de naissains par année.

GÉNITEURS:OSTREA EDULIS

LARVES: OSTREA EDULIS

COURBES DE CROISSANCE DES TROIS ESPÉCES ÉLEVÉS A L'ÉCLOSERIE COQUILLAGES

Ostrea edulis
Crassostrea gigas
Tapes decussatus

NAISSAINS: OSTREA EDULIS

PROGRAMME DE PRODUCTION DE 10,000,000 NAISSAINS HUÎTRE, PLATE: OSTERA EDULIS

Schéma Technique de croissance chez
l'huître plates Ostrea edimos (MAROST)

Partie élevage larvaire

Partie naissains

SHRIMP HATCHERY IN MAROST

By Mr. Rabah BOUKABOUS
MOROCCO

1- INTRODUCTION

In the 30's a pregnant female of shrimp, placed in aquarium, discharged her eggs in a small laboratory in Japan. The nauplii issued, fed on a diatom, arrived to develop into different stages. That was the take up of the shrimp rearing problems. The technical procedures reached its practical level on the 60's. The controlling of mass production of micro-algae and the adoption of the brine shrimp, as live foods, and the use of artificial food pellet are the principal components of the actual shrimp hatchery industry.

The entire shrimp farming in the world then shifted. After depending on the wild seed supplies which are sensitive to many ecological fluctuations, the farms started taking advantage of the hatcheries output. Then the emphasis was on the hatchery technology. The yearly production of shrimp larvae now amounts to several hundred million. Many species are exploited all over the world especially in the South East Asian regions (Taïwan, Japan, Thailand, Philippines,…) and the Latin American countries (Ecuador, Peru, Brasilia,…) dealing with many species, penaeid shrimp particularly.

It is always the same story in marine aquaculture. The wild broodstocks and then the natural seed supplies may desappear rapidly due to human operations or simply to natural fluctuations. Hatcheries can take over of nature and have considerable part in the success of the shrimp farming industry.

In order to make people familiar with what is shrimp seed production hatchery, we'll describe in this report the main installations with the emphasis on their maintenance. We'll also set our the major daily operations carried out in shrimp hatcheries. Obviously, this should be adapted to local conditions and are intended to be developed in associations with common sense, experience and proper management.

2- INFRASTRUCTURE

To help the hatchery management, infrastructure should be directed towards the efficiency of efficiency of the installations and their maintenance in clean conditions. Bacterial contamination are usually among obstacles in hatchery production and their propagation could provoke serious problems.

2.1- Pumping

The choice of pumps should be carefully made to ensure required water flow, simple use and maintenance and energy cost saving. One other pump, at least, should be ready for use in case of the main pump breakdown. The main pumps should be alternately used to allow equal running thus eliminating excessive standing. Pumps should be sea water resist and can be coated with an epoxy layer to diminish electrolysis.

2.2- Filtering

In general, sea water filtration of 100 μm to 150 μm is sufficient for larvae rearing and many kinds of apparatus can be used: sand, cartridge of bag filters. As for artemia and purely algae culture, it is recommended to provide I μm filtered sea water.

The filters should be cleaned after each use. Experience with sea water filtering showed that regular treatment of filters with 5.25% hypochlorite solution for a period of 1½ hour is highly suggested in order to maintain them in proper operating conditions.

2.3- Pipes

Polyvinyl Chloride (PVC) pipes are, by far, the most common material used in every hatchery. Pipes design and dimension should be determined carefully, taking in account eventual modifications (commonly observed in hatcheries). It should be as simple as possible avoiding too much bends and tees and provided with unions so it can be easily cleaned and taken down. It is necessary to clean the hole system on a weekly basis. Sponge «pigs», previously wet in an hypochloride solution can be used to clean efficiently inside of the pipes.

2.4- Tanks

Fiber glace or concrete tanks can be constructed. Their capacity and number depend upon intended larvae production and number of gravid female available in one day. Rectangular tanks of 100 m³ (2 m deep) seem to be the most convenient for culture management. A bottom slope of 2% of 3% is required to drain the water easily.

Sea water for larvae and brine shrimp tanks should be heated to a certain temperature. In general, electric heating offers more convenience (easy use and control), however, the use of fuel as energy source remains the most economical solution.

All the tanks must be aerated. Blowers installed for this purpose must offer sufficient air at sufficient pressure. It is recommended not use any metallic material.

2.5- Control system

This system might be of crucial importance. It allows control of all the equipment's functioning (pumps, blowers,…) and regulates other factors such as temperature, light… An alarm system associated to each control pannel will be of great help. The hole system should be placed in a room protected from dust and humidity.

3- HATCHERY PRODUCTIONS TECHNIQUES

We'll describe here some of the experience we had dealing with P. japonicus seed production in a pilot hatchery. The techniques states hereafter may be considered as basic operations for shrimp hatchery management, however, as it was pointed before, it must be remembered that this should be developed and adapted to each particular conditions.

3.1- Broodstock

3.1.1- Artificial maturation

One of the problem facing hatcheries consists on obtaining gravid females in a certain quantity at a certain time. The primary results we had with artificial maturation could be significantly considered.

Adult shrimps, kept in enclosures in the lagoon, are introduced into artificial maturation tanks during October: 60 females and 40 males of more than 30 gr. in body weight are placed in a tank at 8 shrimps per square meter. For the purpose, circular tanks (4,5 m in diameter and 1.23 m in depth) were made by MAROST polyester department. The tanks are equipped with an air-lift system composed by circular and performed PVC tubes installed on the bottom. The hole system is then covered with a perforated plate which supports successively a screen of 1 mm mesh, a shell layer of 3 cm depth, another screen of 1 mm mesh and rivers sand 10 cm thick.

The air-lift system allows water circulation from up to down when air is used by night and from down to up when the system is provided by sea water during the day at a rate of 150% renewal.

All the tanks are covered with black canvas sheet and provided with neon lamp in order to maintain photoperiod and water temperature. These factors are programmed and automatically controlled.

Feeding the animals is done 1 time in the evening. Fresh food (squid, clam, small shrimp,…) are distributed at 50% of total biomass. Sometimes, artificial food pellets are given at ration 1%. These values are adjusted every day depending on the remaining food in tanks.

By the end of March, females gonades reach the final stage of maturation. The spawners are then selected and transferred to the spawning tank.

3.1.2- Natural maturation

Every year best lots of most-larvae are selected to be broodstocks. They are kept in 1,000 m² enclosures in the lagoon. Feeding is composed of squids, oysters, small shrimps… and artificial pellets at the same ratios as mentioned above.

In general natural maturation is achieved by May–June. Gravid females are then selected, spawners with thick ovary, dark in color and clear in contour are chosen and transported to the hatchery for spawning.

3.2- Spawning

The gravid females considered to be ready for spawning are gathered and transferred to spawning tank by the evening. The tank contains sea water at 22–24°C and covered with a clack plastic sheet. The temperature is then raised gradually to 28–29°C. Usually spawning occurs at midnight of the first or the second day. In the morning following spawning, shrimps are removed. If there is no eggs by the second day, the females are transferred to maturation tank for further spawning.

Since P. japonicus eggs are benthic, strong aeration should be given to examine them. Eggs are then counted and their quality checked. Viable eggs of P. japonicus are spherical and translucent ranging from 170 to 230 μm.

In the afternoon just prior hatching, naupliis are observed to move intermittently in normally developed eggs. If the eggs quality is not satisfying (abnormally developed eggs, not fertilized eggs,…) the spawning tank is emptied.

3.3- Larval rearing

3.3.1- Naupliis

In normal conditions, hatching rate of the naupliis exceed 50%. At this stage the larvae grows by its own yolk and no food is given. Naupliis are easy to count by picking up randomly several samples using 250 ml beaker. The naupliis metamorphoses into the zoea stage after 36 hours molting 6 times.

3.3.2- Zoea

Zoe larvae feed on microalgae, diatoms especially. Several species were used:

• Chaetoceros gracilis

• Skelethonema costatum

• Tetraselmis suesica

Algae are applied at last naupliis stage so there will be no leak of food to the zoea stage. The larvae swim continuously forward and drag a thread-like feces. When the larvae reach the zoea three stage is start feeding on brine shrimp naupliis (artemia AF). The zoea larvae takes four days before molting in mysis. The zoea stage is very delicate and offently culture failures are observed at this period. At that moment, the situation is generally irremediable and we start all over again.

3.3.3- Mysis

The mysis larvae grow to postlarvae stage after three phases named Mysis 1, 2 and 3. During this period larvae feed on diatoms and brine shrimp artemia. Experience confirmed that the use of diatoms and artemia as foods for the larvae results in better growth and survival. Artemia is given twice day until the PL 10 larvae stage.

3.3.4- Post-larvae

The larvae is now carnivorous and feed on all active small animals in the tank. For instance, at this stage more than 50 artemia per day can be consumed by one larvae. At PL 5, fresh food like squid clam, small shrimp… is given to the larvae. When the larvae reach PL 10, feeding can be entirely shifted to artificial and fresh food stopping artemia. Pellets size depends on the age of larvae: PL 10 to PL 15: 170 to 300 μm - PL 15 to PL 20:300 to 500μm - Pl 20 to PL 40:500 to 1,000 μm and more than PL 40, l to 2mm.

Fresh foods play an important role as feeding items but care should be done to maintain suitable water quality. Tanks are thus siphoned each morning to take out the remaining food and dead larvae.

Since we are dealing with «enclosure» growing out systems, the Postlarvae are kept in the hatchery until they reach PL 50 or more. They are then recolted by emptying the tank through a special screen, counted and transferred to «enclosures». 20.000 Postlarvae are transported in 500 liters tanks with oxygenated sea water.

The general guideline hereafter indicates the main important operations in shrimp hatchery. It may deal to acceptable results in normal condition. This simplified picture must be, however, changed and adapted to local conditions.

GENERAL SHRIMP HATCHERY GUIDELINE

(*) quantity per 100.000 pl.

(**) % of total biomass