II. CONFERENCES (continued)

8. Artificial propagation (continued)

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 Shehadeh & Kuo (unpublished data) had some success with the nauplii of Artenmia salina fed alone on the seventh day after hatching, but the results were later improved with a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 marcrolepis fed exclusively on copepods but grew best on copepods prepared in association with an algal bloom, particularly Chlorellaspecies.

Table 8.3 Experimental foods for larvae of grey mullet species, tried at one time or another

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 artificial 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. Blaster (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.

Houde (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 problem 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 & MeVey (unpublished data) successfully reared the larvae of Siganus canaliculatus at a density of 5/l. The data in Liao (1974) indicated effective rearing at a density of less than 10 larvae/l. Each individual larval from 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. Observation 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. macrolepis. However, the effect of salinity of larval survival and development is possibly more significant than that for incubation of the eggs.

Liao et al. (1971) reduced the salinity from 31 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 and 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 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 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 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 (see 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 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 influences 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/l initially, with a final density of between 5 and 50/1 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 veraciously 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 result obtained by Kuo et al. (1973 a). 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 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 first 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 does. 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 the 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 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 of wet methods.

About one million eggs per female are released. Fertilization can be estimated one hours 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/l. 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 32–55‰ 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 prefered.

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 100–250 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 artificial food can then be used. The density of the larvae in the rearing kreisels at transfer should be no more than 6/l, with an anticipated larval density at day 21 of about 0.33/l.

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, polyethlene and butyllined 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 l 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 on more than 1400 lux at the surface. Regular illumination with separate control should be available.

Temperature controls should be available to maintain the air and water temperature at 20–22 °C although there are indications of improved growth at 24 °C from day l. The initial salinity of the sea water in the tanks should be 32–55‰. 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 μg and hydrogen sulphide up to 5.00 μg at day l. 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 probable 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 hardly 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 1.25m³ 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/ml at stocking a total of nine tanks of 10m³ 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 problem 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 larva/l 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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Vodyanitskii, V. A. & Kazanova, I. I. (1954). The identification of pelagic eggs and larvae of Black Sea fishes. Tr. Vses. Nauchno-Issled. Inst. Morsk. Rybn. Khoz. Okeanogr. 28, 240–325.

Wallace, J. H. (1974). Aspects of the biology of Mugil cephalus in a hypersaline estuarine lake on the east coast of South Africa. In Proceedings of the IBP/PM International Symposium on the Grey Mullets and their Culture, Haifa, 2–8. June 1974.

Walne. P. R. (1958). The importance of bacteria in laboratory experiments on rearing the larvae of Ostrea edulis. I. Feeding experiments. J. Mar. Biol. Assoc. UK 43. 767–84.

Wimpenny, R. S. & Faouzi, H. (1935). The breeding of a grey mullet, Mugil capito Cuv., in Lake Qarun, Egypt. Nature, Lond. 135 (3425), 1041.

Yang, W. T. & Kim, U. B. (1962). A preliminary report on the artificial culture of grey mullet in Korea. Proc. Indo-Pac. Fish. Counc. 9 (2/3), 62–70.

Yashouv. A. (1966). Breeding and growth of grey mullet (Mugil cephalus L.). Bamidgeh 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.

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Yashouv. A. & Berner-Samsonov, E (1970). Contribution to the knowledge of eggs and early 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 Proceeding 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-juy Basilewsky) in Peter the Great Bay. 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

3.1. Temperature

Overwintering necessary in certain cases

Under 15° C avoid handing (very susceptable to disease caused by brusing on the skin

3.2 Salinity

Tolerance species dependent

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 block peritoneum (The flesh is red all through)

It is similar to bream Chrysophrys major

it is the progeny of a O. niloticus × O. mossambicus (mutant) cross.

At 15 – 20 g, it can be transferred to full strength sea water over 4 few days

5. GROWTH

Males grow faster than females stunting can occur in ponds

6. REPRODUCTION

Problems:

1. males agressive/ territorial presents problems in hybrid crossing
2. precocious maturity in reared fish

Some figures relating to reproduction are given below :

REPRODUCTION

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

1. Sufficient number
2. Graded size groups
3. All male

8. MANAGEMENT OF BROODSTOCK

8.1 Temperature 23° C higher must be respected

1. Equatorial regions-production continuous
2. Sub-tropical and high altitude tropical regions-production restricted to warm months.

Thermal shock can induce spawning.

Some species are very sensitive to temperature, in terms of 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

-   Could be advantageous

Maximum for fry production:

S. aureus 4 – 5‰     -   S. mossambicus 10 – 13 ‰

8. 3. Food

The feeding of the broodstock is fairly 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 no 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.

8.4. Stocking density

High stocking density depress spawning

Exploitable but problematic For large scale fry production

2 factors must be considered :

Some examples

9. PRODCUTION OF ALL MALE FRY

9.1. Hormone treatment

Androgens: 17 α-methyltestosterone (MT)

Genetic females → functional males

Genotypic males : unaffected

Administration : via food 30 – 60 mg/kg of fond 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

such handling reduces reproduction capacity

Problems:

Difficult to maintain purity of stocks, selection of pure stocks, time consuming, lower fecundity (66 %) of hybrid crosses.

9.3 Intensive selective grading

Continuos selection for faster growing males (at least every month)

10 FRY PREFATTENING

Range of conteiner designs 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 3³/hr (depends on oxygen requirements)

A = Area of raceway (m²)

R = Number of water changes/hr

11. STOCKING RATES

Some realistic production in intensive systems:

* 1. Allows for enhanced individual growth rates to produce larger fish

* 2. Faster growing 50 % are ongrown (70 % males)
2 harvest a year
Slow growers find alternative use

12. CAGE CULTURE

Curbs reproduction. Can result in food losses. A variety of species have been tried.

Range of recorded yields under experimental and commercial conditions :

Max. stocking density:

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 FOR 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:

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 - Powered diets - first feeding
Wean on to granular food,
Then 3 mm size peliets.

Tilapia have no stomach, therefore they feed several times per day.

SOME SELECTED REFERENCES OF 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 - op . 267–355.

BALARIIN, 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 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 by FUCHS (1982, 2) shows a clear difference for survival obtained while employing natural inert food (70 %) or dry compound food (40 %).

METAILLER et al (1981) 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 a 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, if 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 please is still delicate and from time to time accidents can occur.

It must be remarked that early weanings 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. MORINIENE (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 larvae 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 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 weight 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 n 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 have 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 direct 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 Inosine 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 is 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 an influence on the growth after weaning.

2.3. First fattening

Intensive first fattening of Turbot does not cause any particular problem, 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 sea-water 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 try 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

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, 1981

- BROMLEY, P.J. and B.R. HOWELL, 1983
Factor 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'élevage. 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 growth 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 Sales 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 diets. J. World Maricult. Soc. 12 (2) p. 11 – 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, 1983
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.