Premiers resultats de l'elevage en cages de Tilapia nilotica (L.) dans le Lac Kossou,Cote d'IvoirePreliminary results of cage rearing Tilapia nilotica (L.) in Lake Kossou,Ivory Coast

The experimental rearing of T. nilotica in 1-m³ cages floating in Lake Kossou, Ivory Coast, was performed between March 1974 and April 1975. The fish were fed water-stable pellets (24.7% protein), the daily ration generally varying between 6 and 3.4% of the ichthyomass present. Fingerlings (9–55 g each) were stocked at densities of 200–400 fish/m³. They reached commercial size (more than 200 g) within 4–6 months, depending on the biomass present in the cage (stocking density and average individual weight of fish), as well as on limological conditions. The average annual mortality was 5.9%. Annual production varied from 36 to 64 kg/m³. The feed conversion rate averaged 2.8. A reduction of the daily ration for fish larger than 40 g reduced this value.Fingerlings should average at least 20–30 g in weight at initial stocking of the cage. Two crops a year can then be easily realized. If only male fish are reared, three harvests per year appear to be possible, increasing the annual cage production of fish close to 200 kg/m³ with proper management.The possible development of T. nilotica cage culture is actually hampered due to the lack of adequate fish feed available commercially, and to the lack of sufficient quantities of calibrated fingerlings throughout the year.     

Les antibiotiques dans les elevages de larves de bivalves marinsAntibiotics in larval rearing of marine bivalves

Fifty publications (1956–1976) concerning the use of antibiotics in rearing marine bivalve larvae are analysed. Most of the existing antibiotics have been tested alone or in combination, very frequently in an arbitrary fashion and without preliminary study to determine the most suitable antibiotic. The results obtained as regards to the survival of larvae or their growth have been variable, at times contradictory and not repeatable.The problems posed by the utilisation of antibiotics in rearing bivalve larvae are discussed and a standard routine for the use of antibiotics is proposed.     

Analyses sanguines de turbots d'elevage immatures (Scophthalmus maximus L.)Blood analysis of immature cultured turbot (Scophthalmus L.)

A study of cultured healthy turbot haemochemistry is based on blood data of 107 twelve- to fifteen-month-old fish. Six successive samplings were carried out in the Centre Oceanologique de Bretagne (COB) and in two aquaculture experimental stations in Brittany. Turbot were not fed 36 h before sampling.Thirteen parameters were studied: in the blood, haematocrit and haemoglobin, and in the plasma, glucose, total protein, total cholesterol, triglycerides, phospholipids, sodium, potassium, chloride ion, calcium, magnesium and mineral phosphorus. Moreover, electrophoresis of plasma proteins was systematically carried out. Indicative haemochemistry standards are proposed from these results.A parallel is drawn between the present results and previously known haemochemistry data in turbot and other flat-fish.     

Les lagunes ivoiriennesThe lagoons of the Ivory Coast

The first evaluation of the acquired knowledge on the brackish water environment of the Ivory Coast is presented here.Situated along the north coast of the Gulf of Guinea, between 2°50′ W and 5°25′ W, the lagoons have a total surface area of 1200 km². The climate of the coast area is similar to the equatorial climate. The annual rainfall is about 2000 mm and distributed in two rainy seasons. Each of the three main lagoons has a different hydrological system which depends on the contribution of the continental fresh water and on exchange with the marine environment. In the Ebrié lagoon, the annual contribution of the fresh water is estimated to be four times the volume of the lagoon. The entry of the sea water is 14 times this volume.The temperature of the water averages 29°C and varies little throughout the year. In the Ebrié lagoon for example, there is considerable variation in salinity over the area depending on the seasonal contribution of the continental fresh water and the exchange with the sea water. The degree of salinity also depends on the morphology and the bathymetry of the different parts. Many intermediate situations are noted, from high gradients (seasonal and vertical) to low gradients within stable oligohaline areas (salinity from 3 to 5‰. On the contrary, the Aby lagoon is less influenced by the marine environment. The salinity gradient is more stable, and the water is more oligohaline.In the marine influenced area, the seasonal variation of pH is the result of mixing between sea and fresh water. However, a low pH is noted particularly in the western part of the Ebrié Lagoon. The concentrations of dissolved oxygen in the surface water are generally 4–7 ppm. Its vertical distribution varies greatly during the different seasons and over the different areas. Deoxygenation conditions are often observed, for example in some polluted bays in the Abidjan area, and in the central basin of the Aby lagoon. Generally, the desalinated water is characterized by its poor nutrient contents and particularly the lack of nitrate. This phenomenon probably is related to the rapid recycling of the nutrients. The biomass of the phytoplankton is generally very high and the concentration of chlorophyll a represents more than 35 mg/m³ in the western part of the Ebrié lagoon. The corresponding primary production is about 300 mg of carbon/m³ per hour.The zooplankton is represented mostly by the copepod Acartia clausi. The first estimation of the turnover time of the total biomass is between 1.2 and 3.8 days. In the population of the benthos, molluses represent the bulk of the biomass. The importance of some crustaceans—crabs and shrimps—is noted.Among the ichthyologic fauna, there are many types of biological cycles depending on the various types of salinity tolerances and on the conditions of the reproduction cycle. The lagoon stocks are exploited by means of various types of artisanal fishing gear (individual or collective). The estimation of catches for 1977 was about 7000 tons (of which 60% was represented by Ethmalosa), 70% of the total catch is made by purse seines and beach seines. For the three lagoons, the production should probably be 15–20 000 metric tons, despite obvious signs of over-exploitation.Conclusions are oriented towards a discussion of the heterogeneity, the productivity and the fragility of the lagoon ecosystems.     

Changes in structure and fertilizing ability of marine and preshwater fish spermatozoa diluted in media of various salinitiesModification de la structure et du pouvoir fécondant des spermatozoïdes des poissons marins et d'eau douce dilués dans des milieux de différentes salinités

The spermatozoa of various marine teleosts (sea bass, Dicentrarchus labrax; sea bream, Sparus auratus) or fresh water teleosts (trout, Salmo gairdneri; pike, Esox lucius; guppy, Poecilia reticulata) were diluted in media of different salinities. Motility, morphological changes and fertilizing ability were the criteria used in judging the effects of such treatments. The medium best adapted to dilution of sea-fish sperm had a salinity of about 20‰. Sperm motility was increased and prolonged, and fertilization rate was significantly improved (P<0.05) for the sea bass at a $\text{1}\text{1000}$ dilution. For freshwater fish (trout and pike), an extender with about 7‰ salinity increased motility time and fertility ability (P<0.01) as compared to freshwater. After dilution in fresh water the structure of trout spermatozoa was considerably altered (rupture of plasma membrane and mitochondrial swelling). When spermatozoa were diluted in the extender, there were no significant structural changes in trout, but alteration occurred in the mid-piece of the guppy spermatozoon. It is concluded that fresh water or sea water are not the best media for the practice of artificial insemination in freshwater or marine fish. Investigations should be carried out to define the best extender for use in techniques of artificial insemination in fish produced in aquaculture.     

Utilisation de souches bacteriennes selectionees dans l'alimentation des larves de Mytilus galloprovincialis Lmk (Mollusque Bivalve) en elevages experimentauxUse of selected bacterial strains for feeding larvae of Mytilus galloprovincialis Lmk in experimental rearing

The authors studied the possibilities of using several bacterial strains, alive or heat-killed, alone or associated with an algal diet, as food for mussel larvae. Living bacteria offered with an algal culture improved larval growth, whereas the addition of heat-killed bacteria seemed to favour the appearance of an exogenous bacterial infection. Utilization of bacteria without algae sets the problems of their food value under these conditions and the concentration at which they should be used. Therefore, further complementary research will be necessary.     

Etude de la croissance des juveniles de Chrysichthys walkeri (Günther) en etang en fonction de la densiteA study of the growth of juveniles of Chrysichthys walkeri (Günther) in ponds in relation to density

A study of the growth of Chrysichthys walkeri juveniles in relation to density was made with 2520 fry distributed in nine small square ponds. The study was successful in 5 ponds with 1490 individuals.The oxygen level of the water was low especially during the night. The temperature ranged between 28 and 30°C. The fry were stocked in ponds just after yolk vesicle resorption at a weight of 5.4 mg. After 4 weeks, the ponds stocked lightly showed better results (greater weight of the fishes) than the more densely stocked ponds. After 7 weeks, the growth difference between lots was very significant.The fishes were fed with pellets from the first day of the experiment. The total mortality was 38%.     

L'aquaculture en enclos: Adaptation au milieu lagunaire ivoirienAquaculture in enclosures: adaptation to the lagoon system of the Ivory Coast

The author describes the adaptations and modifications brought to fish enclosure culture technology during a preliminary field experiment in the Ivory Coast. Fish enclosure culture needs only relatively low investments and should be easily popularized in artisanal structures throughout the whole Ivory Coast lagoon system, particularly using catfish (Chrysichthys) culture.     

Mise au point d'un circuit ferme en eau de mer pour la survie en laboratoire des jeunes muges (Teleosteens,Mugilidae)Using a recirculating seawatef system for the maintenance of young mullets (Teleostei,Mugilidae) in a laboratory

A recirculating seawater equarium system for the maintenance of young mullets is de-scribed in this paper. The system, with a total capacity of 1 000 1, consists of 36 individual culture tanks, two reservoirs, and apparatus for thermal regulation, filtration, ultra-violet sterilisation, aeration and light.     

Preservation of trout sperm in liquid or frozen stateFlüssig- und gefrierkonservierung von regenbogenforellensperma

A series of experiments to study the preservation of rainbow trout semen in the liquid and frozen state was carried out.For the preservation of liquid semen both undiluted and diluted semen was stored in total darkness at 20° or 4°C under a number of different gasses (air, O₂, O₂ + N₂ (1:1), N₂, CO₂, N₂ + H₂ + CO₂ (8:1:1)). The best results were obtained when storing semen in an undiluted state at 4°C under O₂ (hatching rate after 15 days was 80.6%, controls were 98.2%). Good results were also obtained under air (after 9 days 94.7% vs 94.9% for the controls). Anaerobic conditions, dilution or an increase in temperature all rendered less favourable results.For the purpose of cryopreservation a diluent was developed on the basis of the composition of rainbow trout seminal plasma. The semen was mixed with the diluent immediately before freezing at a ratio of 1:1 or 1:3. The pellet-technique (Nagase, 1964) was found to be more convenient and successful than freezing in straws. The pellets were thawed in a 1% NaHCO₃-solution. The hatching results after storage periods of 1–4 months were very variable (2.6–80.3%).     

Étude de bactéries associées aux élevages de larves de bivalves marinsStudy of bacteria associated with the rearing of larvae of marine bivalves

Eighty-one bacterial strains associated with the rearing of marine bivalve larvae have been isolated from different origins: unicellular algal cultures; filtered sea water; unhealthy larvae; Mytilus edulis spawn, and contaminating strains from the laboratory atmosphere.The ecological, biochemical and nutritional characteristics and the sensitivity to antibiotics of these strains have been studied with the aid of 115 tests. This population appears to be similar to comparable populations studied by other authors.However, complementary studies taking into account the quantitative and qualitative variations of each source of bacterial contamination have been shown to be necessary, and are now in progress. When complete, more efficient bacterial control of the breeding of marine bivalve larvae will be possible.     

Elevage des larves de Loup (Dicentrarchus labrax, L.) a l'aide d'organismes du zooplancton congele: Resultats preliminairesRearing of sea-bass (Dicentrarchus labrax L.) larvae on frozen zooplankton: Preliminary results

Larvae (fry) of sea bass (Dicentrarchus labrax L.) were successfully reared from the mouth-opening stage to the age of 120 days being fed only on frozen zooplankton (Rotifera, Copopoda and Daphnia). This inert food is well accepted when left in the water less than 4 h after being thawed, but is rejected afterwards. The larval development can be compared to that obtained by artificial food and the survival rate is similar to that obtained by living plankton.     

Regards sur l'aquaculture mondiale: Exposé introductif à la réunion de la Fondation Internationale pour la Science sur l'Aquaculture - Abidjan,Côte d'IvoireSome comments on aquaculture world-wide

After some definitions of aquaculture terminology, some quantitative data are given concerning world-wide aquaculture — annual production 6 million tonne (1975). In addition specific production details are presented for the most important aspects: fish breeding, shellfish breeding, crustacean breeding, and culture of aquatic plants.The future of aquaculture is considered in production terms: 20 million tonne expected in 1985 and 50 million in the year 2000, in order to supplement the resources resulting from marine fishing.However, aquaculture is subject to risks, especially in Africa, due to a lack of hydrobiological, ichthyological and zootechnical knowledge, to which are added problems of a sociological and juridical nature.     

Morphogenese de l'appareil digestif et de la vessie gazeuse du turbot, Scophthalmus maximus L.Morphogenesis of the digestive system and swim bladder of the turbot, Scophthalmus maximus L.

The study is based on serial sections made on turbots raised at 18 ± 0.5°C from day 1 (post-hatching) to day 20. Histological changes of the digestive system and swim bladder were observed on a daily basis.At day 1, specimens (total length, Lt = 3.0–3.1 mm) present a digestive tract undifferentiated along its length and closed anteriorly. They belong to the embryonic period in spite of the presence of associated digestive glands (liver and pancreas).The larval period extends from day 2 to day 14–15 (Lt = 3.5–7.0 mm): the swim bladder differentiates and inflates, then the pneumatic duct binding the swim bladder to the stomach degenerates; regional differences appear along the digestive tract which starts to be functional.From day 15–16 (Lt = 6.9–7.7 mm) the juvenile period begins with the formation of gastric glands and the onset of gastric digestion. Two pyloric caeca are clearly visible and the number of intestinal folds and goblet cells increases progressively.     

Supplemental feeds containing coffee pulp for rearing Tilapia in Central AmericaAlimento suplementario conteniendo pulpa de café para la crianza de Tilapia en Centro America

A supplementary feed containing 30% coffee pulp was evaluated for use in the culture of Tilapia aurea in El Salvador, Central America. A comparison of the coffee pulp feed with a feed containing all of the same ingredients except coffee pulp was made with T. aurea raised in 1.0-m³ cages suspended in a fertilized earthen pond. Survival was high in all treatments and there was no significant difference in average weight gain between groups of fish receiving the two experimental feeds. Production trials were conducted in 100-m² fish pens and in 0.05-ha earthen ponds. Pen-raised fish receiving coffee pulp feed grew faster throughout the experiment, and total production was approximately twice that in control treatments. Highest production in pens was 1.25 kg/m² per year. Results of production pond trials using T. aurea at 9 000/ha and stocked with the piscivorous Cichlasoma managuense yielded an estimated 3 392 kg/ha per year in fed treatments and 2 049 kg/ha per year in controls. Low feed conversion (1.92) and low feed cost resulted in an increase in net annual earnings of $251.00/ha.     

Etapes du developpement embryonnaire et larvaire du sar, Diplodus sargus L., en elevageStages of the embryonic and larval development of the white sea bream, Diplodus sargus L., in rearing conditions

Eggs of white sea bream (Diplodus sargus), taken from wild parents, were incubated and, after hatching, produced larvae which were then reared up to the fry stage. The different stages of development during the embryonic and larval periods are described. Some characteristics of the eggs (buoyancy, duration of incubation, critical periods) and of the larvae (metrical characters) are reported.     

Incubation experimentale et developpement embryonnaire de la daurade royale, Sparus aurata (L.), a differentes temperaturesIncubation and embryonic development of gilthead bream, Sparus aurata (L.), at a range of temperatures

Eggs of raised gilthead bream, Sparus aurata (L.), were incubated to hatching at various temperatures ranging from 7.7°C to 26.3°C. For four stages of development, the relationship between temperature and incubation time is given. Time from fertilization to hatching varies from 135 h at 11°C to 40 h at 21.3°C. In our experiments no egg hatched below 11°C or above 22°C. The highest hatching rate and the lowest rate of larval abnormalities were both observed at 14.5°C which is also the spawning temperature.     

The influence of temperature and wet weight on the oxygen demand of rainbow trout (Salmo gairdneri R.) in fresh waterInfluence de la température et du poids vif sur la demande en oxygène de la truite arc-en-ciel (Salmo gairdneri R.) en eau douce

Multiple regression analysis was applied to a series of oxygen demand measurements on rainbow trout. It confirmed the determinant influence of temperature and size of fish under standard feeding conditions. Two types of adjustment of oxygen demand in relation to those two factors were tested, and one of them was choosen in which the temperature is under an exponential form. This allows the introduction of the Q₁₀ concept. The value of Q₁₀ is 3.5 when the water temperature is below 10° C and 1.7 above 12° C.