The chromosomes of three commercially important species of veneroid bivalves were studied: Cerastoderma edule (Cardiidae), Venerupis pullastra and Venerupis rhomboides (Veneridae, Tapetinae) using conventional Giemsa staining and morphometric measurements. C. edule showed a diploid chromosome number of 2n=38 and a variable occurrence of supernumerary chromosomes. Its karyotype consists of 12 submetacentric, 4 subtelocentric and 3 telocentric chromosome pairs. The supernumerary chromosomes were easily distinguished by their reduced differentiated size and by their intra and inter-individual variability. C. edule is the first bivalve species where supernumerary chromosomes have been observed. V. ullustra had 2n = 38 with a karyotype including 3 metacentric, 8 submetacentric and 8 subtelocentric chromosome pairs. V. rhomboides had 2n = 38 with a karyotype including 4 metacentric, 8 submetacentric, 4 subtelocentric and 3 telocentric chromosome pairs. Cytotaxonomic relationships are proposed within Tapetinae from comparative analysis of karyotypes of two species studied here and three other species of the same subfamily previously studied.

Two techniques of stock discrimination both utilizing scales, i. e. termed as classical technique and shape analysis, are compared for discriminating between North American and European Atlantic salmon (Salmo salar L.) caught off West Greenland. Three scales from each of 60 salmon were analyzed: 30 from North American and 30 from European-origin salmon collected from home rivers in 1982. The best results indicated misclassification and error rates of 0% for shape analysis and 5.0% and ± 1.7%, respectively, for the classical technique. A nested ANOVA indicated that variation was greater between scales of salmon of North American and European origin than from several scales from the same salmon. It was concluded that shape analysis with computer-aided devices may be superior to the classical technique and it is recommended that it be examined for use at West Greenland.

Spatial closures are commonly used by Australian fisheries managers to alter fishing patterns. To evaluate different fishing closures, however, fishery scientists have to understand and model the spatiotemporal interactions between fish stocks and fishing fleets. We develop a deterministic, stationary, per-recuit, age-structured simulation model to assess different spatial closure strategies, and use date from the Torres Strait tiger prawn fishery, Penaeus esculentus, as a working example. Our results show that selection of an optimum spatial closure largely depends on the relative importance given to changes of the different utility functions evaluated (yield, value, egg production). We show that, on average, with a spatial closure yield-per-recruit would decrease, but also show that value-per-recruit may increase 10% with the appropriate closure. Our results suggest that egg-per-recruit would always increase in the presence of a closure. By incorporating parameter uncertainty within the simulation model we predict the uncertainty associated with alternative closure strategies, and thus provide valuable information for the decision-making process.

Les variations mensuelles des captures de crevettes Penaeus notialis (Perez Farfante, 1967) entre 1962 et 1984 et les variations annuelles entre 1965 et 1984, dans l'estuaire de la Casamance, ont été étudiées. Les salinités extrêmes de 0,8 et 69 ‰ ont été enregistrées durant cette période. Les crevettes sont pêchées pendant leur migration de retour vers la mer, à l'aide de filets à maille de 12–14 mm de côté, fixés de part et d'autre de pirogues ancrées. Les données de salinité étant rares, une corrélation a été recherchée entre la salinité et la pluviométrie de manière à pouvoir utiliser les données de pluviométrie, disponibles pour chaque année. Il y a deux maxima de captures durant l'année. Lorsquela pluviométrie est importante (1,25–1,50m) ils sont observés en milieu d'année, quand la salinité est la plus élevée. Au contraire, lorsqu'elle est faible (0,75 à 1 m) les maxima se situent plutôt vers le début et la fin de l'année. Quand la pluviométrie est moyenne (1 à 1,25 m) le premier maximum survient en mai et le second en septembre-octobre. Les captures annuelles sont bien corrélées, négativement, avec l'indice pluviométrique qui détermine la salinité au premier semestre (pluviométriemoyenne des deux années précédentes). Cependant, en 1984, alors que la valeur de l'indice était très faible (0,795 m), les captures se sont effondrées. Aussi est-il supposé qu'il existe une relation parabolique entre les captures et la pluviométrie. Les captures maximales sont obtenues alors que l'estuaire est sursalé toute l'année par rapport à la mer. Les variations des captures pondérales traduisent celles des captures numériques et, dans une large mesure, celles du poids individuel des crevettes pêchées.

Le modèle composite, communément admis pour décrire les deux stances de croissance de l'albacore dans l'Atlantique Est, est ré-examiné. La valeur du paramètre t0 est corrigée. L'équation de croissance est exprimée en fonction d'un âge conventionnel. Les limites de ce modèle sont soulignées. Différents modèles continus sont ensuite ajustés sur les données de Capisano et Fonteneau (1991), qui estiment l'âge par décomposition polymodale des fréquences de tailles des captures réalisées par les senneurs, durant la période 1983–1988. On montre que l'ajustement des modèles à 3 ou 4 paramètres (Gompertz, Richards et Von Bertalanffy généralisé) est peu satisfaisant. On propose un modèle à 5 paramètres, combinant une fonction linéaire et une loi de Von Bertalanffy généralisée. La validité et l'ajustement de ce modèle sont analysés. Il permet de décrire correctement la croissance dans l'intervalle 40 à 150 cm de longueur à la fourche et 0,25 à 4,25 ans. Afin de disposer d'une équation unique, couvrant l'ensemble de la phase exploitée jusqu'à 170 cm de longueur et 6,0 ans, le modèle est ré-ajusté à des données simulées à partir des modèles précédents. La croissance au sein de la phase exploitée s'exprime alors comme suit :

L(t) = 37,8 + 8,93×t + (137,0 - 8,93×t) × [l - exp(-0,808×t)]7,49

La fiabilité de cette équation est discutée, en relation notamment avec l'existence probable d'un dimorphisme sexuel de croissance. Des hypothèses sont développées pour expliquer l'existence d'une stance de croissance juvénile lente, suivie d'une accélération de croissance au voisinage de 47 cm, puis d'un point d'inflexion au voisinage 90 cm. En particulier, la succession des 2 stances de croissance semble liée aux migrations de l'espèce, à l'intérieur de l'Atlantique Est et vers l'Atlantique Ouest.

Seasonal growth of juvenile oysters (Crassostrea gigas) kept in an intensive upwelling system was studied from 1984 to 1986 in 60 to 90-day growth experiments. Saline ground water was used to produce Skeletonema costatum which was injected as food into the water supplying the upwelling system. Oyster density, water flow, phytoplankton concentration, temperature and frequency of food addition were controlled. Oyster growth was analysed with multidimensional contingency tables and correspondence analysis. The factors, in order of decreasing influence on growth, were temperature, food concentration and oyster density. A rearing strategy was deduced from the growth analysis for summer and winter. In summer, the density of 120,000 oysters/m2, the flow rate of 1 liter/d/oyster and the food concentration of 0.5 × 109 phytoplankton cells/litre gave the most interesting results. The oysters grew from 0.014 g to 2.2 g after 60 days. In winter, the heat exchanger was necessary to increase the temperature from the 5 °C naturally observed to the 11 °C required for valuable growth. Oyster density and food concentration were the same as in summer. For a flow rate equal to 3 liter/day/oyster, oysters grew from 0.01 g to 0.5 g within 100 days. The cost and profit computations were derived from these strategies. It was concluded that this type of nursery would be profitable in spring, summer, and autumn but not in winter due to the high cost of heating the water.

Samples of trout (Salmo trutta L.) were taken from four rivers in the Conwy system, North Wales: the Roe and the Nant-y-goron, which support sea trout stocks, and the Iwrch and Machno which are situated above impassable waterfalls and contain resident trout. Tissue samples from the fish were used in electrophoretic analysis of enzymes. Fourteen loci were scored of which six were polymorphic (Pgi-2, Gpd-2, Ldh-5, Mdh-2, Mdh-4 and Ck-2). Allele frequency data from these loci were used to test interpopulation heterogeneity, which indicated that the two upstream samples were probably reproductively isolated from each other and also from the downstream samples. Mean heterozygosity was generally lower in the upstream stocks compared with the sea trout populations. UPGMA cluster analysis based on Nei's genetic distance (D) revealed a clear dichotomy between those stocks above, and those below waterfalls. This was best explained by the presence of two strains of trout in the system. One strain, the resident trout occurring above impassable waterfalls, was characterized by high frequencies of the Ldh-5(100) allele, the other strain, principally consisting of sea trout, exhibited high frequencies of the Lhd-5(90) allele.

Cette étude analyse le rôle de la seconde et petite saison d'upwelling dans les changements récents de l'écosystème pélagique côtier ivoiro-ghanéen. Depuis le début des années 1980, les captures de Sardinella aurita ont nettement augmenté au Ghana et en Côte-d'Ivoire ou les modifications de l'abondance et de la dynamique de l'espèce ont été les plus surprenantes. La taille des poissons a augmenté et l'activité reproductrice de l'espèce est maintenant d'une intensité équivalente pendant les deux saisons d'upwelling. On observe, entre 1970 et 1990, une tendance à la diminution de la différence entre l'intensité des deux saisons d'upwelling. Le rôle croissant de la petite saison d'upwelling dans l'écosystème permet de donner une interprétation aux changements observés. Cette saison, plus intense en Côte-d'Ivoire qu'au Ghana, intervient en effet pendant la période de l'année défavorable pour la productivité de l'écosystème pélagique et peut être comparée à un "goulot d'étranglement" pour cette productivité.

Commercial fish species from the east Nigerian coast were examined for external lesions and flesh parasitic infections that may affect their consumability. Altogether, 2 886 specimens from 43 species representing 34 genera were sampled. The occurrence of lymphocystis disease in the pleuronectiform Cynoglossus senegalensis is here reported for the first time from an African marine teleost. Other external lesions of fishes encountered were fin rot, granulomas, pseudotumours and ulcers with total prevalences not exceeding 1%; The following commercial fish species were infected by muscle parasites at the given prevalences: Cynoglossus browni (metacercariae, 18%, Capillaria spinosa eggs, 27%; Echinocephalus sinensis L3 larvae, 9%; Philometra beninensis, 27%); C. senegalensis (Kudoa sp., 10%; metacercariae, 87%); Pseudotolithus brachygnathus (Hysterothylacium sp. larvae, 2%); P. senegalensis (Poecilancistrum cf caryophyllum plerocercoid, 1%; Philometra beninensis, 1% P. typus (Kudoa sp., 3%); Synaptura cadenati (Echinocephalus sinensis, 12%); Stromateus fiatola (trypanorhynch plerocer-coid, 44%); Epinephelus aeneus (didymozoid trematode, 44%; Hysterothylacium sp. larvae, 6%). Capillaria and Echinocephalus, representing helminths with zoonotic potential, present low risks to publie health due to their low prevalences and the local methods of preparing fish for consumption. Apart from C. spinosa eggs in soles and trypanorhynch plerocercoids in S.fiatola, none of the other flesh parasites are likely to affect the market value of their hosts at the recorded levels of occurrence. Carcharhinid sharks influence the occurrence in the locality of most fesh-parasitic helminths for which they serve as definitive hosts. The absence of the third stage larvae of zoonotic Anisakidae common in marine fishes from many other parts of the world is related to the unavailability of suitable hosts. Compared to the results from most temperate locations where similar studies have been carried out, the present study shows remarkably low prevalences and diversity for external lesions and flesh parasites in West African marine fishes.

Une analyse des correspondances multiples et une classification ascendante hiérarchique ont été utilisées pour étudier les variations de rendements par espèce entre 1972 et 1989 de navires de la pêche chalutière hauturière française. L'application de ces méthodes permet de mettre en évidence les relations parfois complexes qui lient les rendements des principales espèces débarquées au sein des rendements totaux et de dégager une partition des profils de rendements caractéristique de cette période. Les facteurs comme l'année et les secteurs de pêche sont ceux qui expliquent le mieux les variations observées; les variations saisonnières jouent un rôle secondaire. Les rendements augmentent et se diversifient entre 1972 et 1989. L'étude montre que ces évolutions peuvent être reliées pour une part à des changements dans les stratégies d'allocation d'effort de pêche et dans la composition des flottilles. Les chalutiers qui exploitaient traditionnellement le golfe de Gascogne au début des annéessoixante-dix ont reporté leur effort sur des secteurs situés plus au nord (nord de l'Irlande et ouest de l'Ecosse) et ont été remplacés par des chalutiers de taille et de puissance plus importantes. Dans les années quatre-vingt, une autre composante fait son apparition. Elle est constituée par des chalutiers de taille plus réduite qui exploitent des secteurs plus côtiers que les précédents.

Different random samplings were used to assess the biomass of intertidal bivalves on two main biotopes of the south west coast of New Caledonia. Over the 46.5 km line of sandy beach, the total bivalve biomass is 4.3 ± 1.8 t and the mean biomass of Atactodea striata is about 3.2 ± 1.2 t. Over the 9.85 km2 sandy-muddy shore of the study area, bivalve stocks (1.050 ± 392 t) are dominated by Gafrarium tumidum and Anadara scapha; their mean biomasses are respectively 270 ± 132 t and 418 ± 308 t. This resource is expected to meet the demand of the domestic market through an artisanal fishery.

Triploid hybrids between female rainbow trout (Oncorhynchus mykiss) and male arctic char (Salvelinus alpinus), together with triploid and diploid rainbow trout controls from the same dams, were tested in freshwater farming from fry stage up to the age of 3 years. When farming was operated in cold water, the survival rate of the hybrids was as good as those of the diploid and triploid rainbow trout. Hybrid growth was noticeably hindered relative to that of diploid controls at the beginning of the juvenile period, but this was partly tempered later on by the effect of diploid sexual maturation; at 3 years of age, the hybrid weighed 20% less than the diploid rainbow trout and did not differentiate significantly from the triploid rainbow trout. The impairment of sexual maturation was very much the same in the hybrid as in the triploid rainbow trout, and dressing traits were therefore quite similar, despite a slight difference in perivisceral fat losses of immature individuals, to the advantage of the hybrid. These results allow one to consider the suitability of this hybrid for large-sized fish production in cold water farming.

Factors influencing the spatial distribution of the bivalves Atactodea striata. Gafrarium tumidum and Anadara scapha were analysed on the south-west coast of New Caledonia, using a multivariate approach (correspondence analysis). A. striata is abundant on sandy beaches with a high coarse sand content. G. tumidum is preferentially distributed on substrates located close to the lower limit of neap tide and seems to be independent of sediment granulometry. A. scapha adults occur at lower bathymetric levels, with sediment composed of 40% medium, fine and very fine sand, and 30% very coarse and coarse sand. For this species, juvenile migration is suggested by the differential distribution of young and adults.

Rainbow trout juveniles (Oncorhynchus mykiss) were fed diets containing high levels (50, 70 or 100%) of vegetable proteins for 8 weeks. Vegetable protein sources employed were soybean meal, lupin seed meal and corn gluten meal, as well as potato protein concentrate. Nutritional evaluation showed that diets containing 50 or 70% plant protein supported growth rates, fish acceptance and nutritive utilization similar to those of both a whole fish meal diet and a commercial trout feed. A taste panel proved that organoleptic properties of fish were not affected by feeding on diets containing high levels of vegetable feedstuffs.

Atlantic salmon juveniles were subjected to a precocious (day 104 after first feeding) photoperiodic (P) and thermic (T) control. After rearing the fry at 16 °C, constant (16 hours of light and 8 hours of darkness, 16 °C) (C) and shortened simulated natural S photoperiod and temperature regimes were used in a factorial experimental design until transfer to seawater. The growth obtained with constant (C) regimes was better than with S regimes. In all cases, we observed very early (day 141, mid-June) a clear segregation of the population into two different subpopulations. Among the conditions, all the differences between the upper and lower modes were growth-dependent. We observed different developmental trends of the gill (Na+-K+)-ATPase activity: the S regime gave a very progressive increase of the enzymatic activity, while we had a rapid decrease after a first phase of increase with a constant photoperiod. The absolute levels of the gill (Na+-K+)-ATPase activity were slightly lower than those observed in one year-old smolts. However, they are quite similar to those of upper-mode fish that have a good salinity tolerance. After transfer to seawater, fish subjected to shortened simulated temperature and photoperiod had the lowest mortality and osmotic disturbance (after 48 hours and 3 weeks). Although the freshwater phase generally lasts more than 15–17 months for this species in a natural environment, we concluded that it is possible to obtain a good salinity tolerance after 7–8 months, with shortened simulated natural photoperiod and temperature regimes, in spite of the absence of a real smoltification; these regimes, however, must be applied during the "dynamic" presmolting phase when the growth is intense.

Four experiments were performed with carp (Cyprinus carpio) in ponds of 200 m2 to test the effects of lysine supplementation of feeds with a low protein content. The initial mean weight of the carp and their daily rations were equal in all the ponds of the same experiment. In experiments 1 (400 fish/pond, 3 replicates) and 2 (200 fish/pond, 4 replicates), three diets were tested: A. 30% crude protein (1.7% total lysine); B. 25% crude protein + 0.5% lysine-HC1(1.7% lysine); C. 25% crude protein (1.3% lysine). In both experiments diet B resulted in weight gains equal to diet A, 20% higher protein retention and 20% less nitrogen discharge per kilogramme gain. Diet C lagged 10% in gain and excreted 10% more nitrogen than B. In experiments 3 and 4 (200 fish/pond, 4 replicates) the feed protein was reduced further and 5 diets were tested: A, B, C, similar to the former experiments, D. 20% crude protein + 1.0% lysine-HC1 (1.8% total lysine), E. 20% crude protein + 0.5% lysine-HC1 (1.4% lysine). In both experiments the results of groups A, B and C were parallel to experiments 1 and 2. Diets D and E resulted in lower growth compared to diet C (significantly in experiment 4) and increased body fat content. In conclusion, 30% protein in carp feeds, of which half the protein was soybean protein, could be decreased to 25%, by replacing soybean meal by grains, and supplementing lysine and methionine to the level of the 30% control. Growth was not impaired and nitrogen discharge into the environment was reduced approximately by 20%. Further feed protein reduction to 20%, with lysine supplementation, impaired growth rate below that of the unsupplemented 25% control diet, although total N-excretion was reduced even more.

The edge and isthmus of the mantle of Pinctada margaritifera (Mollusc, Bivalvia) were studied using light and electron microscopy from a morphological and histochemical point of view. Six areas with several subareas were differentiated in the mantle edge. One of these areas is similar to the epithelium isthmus. Trials to elucidate the nature of the pigment responsible for the black colour of the shell and pearl indicate a melanin-like material. Possible functions of the distinctive epithelial areas in Pinctada margaritifera mantle are discussed according to available data on the secretion of organic matrix of the shell, protein selerotization and deposition of crystals in some pearl-forming molluscs. Three different epithelial areas in the outer mantle edge of Pinctada margaritifera are probably involved in the sequential processes of deposition of calcite prisms, aragonite fibres and aragonite rhombs.

Deux séries d'expériences ont été menées, les unes en étang de pisciculture, les autres en laboratoire, pour déterminer la relation entre conditions thermiques et durée de l'incubation chez l'Atipa [Hoplosternum littorale (Hancock, 1828)]. En milieu contrôlé, 36 °C constituerait la limite supérieure de la température d'incubation permettant la survie des œufs. La température minimum testée, 24 °C, ne constitue pas la limite inférieure permettant la survie des œufs. La durée minimale d'incubation, évaluée à 36 heures, serait obtenue pour une température d'incubation de 33,6 °C. La quantité minimum d'énergie fournie par l'environnement pour obtenir l'éclosion est exprimée en degrés-heures et s'élèverait à 1 201 °C × h pour la température d'incubation de 31,3 °C. Une typologie du développement embryonnaire de l'espèce, directement inspirée de celle de Ballantyne (1930), a été calée sur une échelle exprimée en °C × h. En étangs, les conditions de température au sein de la ponte, plus élevées que celles de l'air, sont sensiblement identiques à celles de l'eau environnante et relativement stables d'une expérience à l'autre (27 à 29 °C en moyenne). Le temps d'incubation observé sur l'ensemble des 9 nids équipés de capteurs varie de 47 à 54 heures. A temps d'incubation égal, le nombre de degrés-heures nécessaires pour obtenir l'éclosion est plus important en étang qu'en milieu contrôlé. La discussion porte sur le rôle du nid dans la reproduction de l'espèce.

Levels of muscle and liver adenylates, phosphocreatine (PCr), total adenylates (TA) and the adenylate energy charge (AEC) exhibited significant seasonal changes. Fish size and condition factors were significantly different throughout this study; however there were no correlations between fish size or condition factor and metabolite levels. Muscle adenosine triphosphate (ATP), TA and AEC were lowest in winter and positively correlated with temperature; while adenosine diphosphate (ADP) and adenosine monophosphate (AMP) levels were high in winter and negatively correlated with temperature. Muscle AEC's dropped into the stressed range (0.5–0.75) during winter months. ATP/ADP ratios were lowest while PCr/ATP ratios were highest in winter months; indicating that a capacity for phosphate buffering existed and could not account for these low muscle AEC's. Liver ATP, TA, PCr, AEC, and adenylate ratios were lowest in the spring and were not correlated with temperature, but rather coincided with reproduction. Liver AEC's dropped into the lethal range (<0.5) in April; although no fish mortalities were observed. Liver AEC's were lower than muscle AEC's throughout the study. The AEC appears to have some validity as a long-term indicator of physiological status and may have application in monitoring/predictive programs due to its predictable response to seasonal change. However, cautious use is suggested until temperature effects on adenylate metabolism and seasonal effects on metabolic recovery following capture stress can be established.

Les pêcheries du delta central du Niger font l'objet d'une exploitation intensive depuis de nombreuses années. L'analyse des débarquements de poisson pendant les deux dernières décennies laisse apparaître de fortes fluctuations dans la production qui décroît régulièrement de 87 000 t en 1969–70 à 37 000 t en 1984–85. Deux causes peuvent être évoquées pour expliquer ce phénomène : l'apparition de la sécheresse en Afrique et/ou l'augmentation de la pression de pêche. Dans le premier cas, les captures annuelles et l'indice d'inondation des plaines, calculés en fonction du cycle hydrologique du delta (de juillet à juin), sont bien corrélés, ce qui s'explique a posteriori par la composition des captures qui s'effectuent à 69 % sur des poissons de moins de 1 an. Dans le second cas, certains éléments suggèrent qu'il y a eu une intensification importante de la pression de pêche sans que celle-ci puisse être chiffrée. La chute des captures totales ne semble pourtant pas due à une mauvaise exploitation des ressources. Les difficultés ressenties par les pêcheurs : réduction des prélèvements individuels qui passent de 1 900 kg/an en 1966 à 740 kg/an en 1989, nécessité de diversifier les activités en pratiquant l'agriculture ou de migrer vers les lacs de barrage ou à l'étranger, seraient donc dues à des phénomènes naturels (sécheresse) ayant entraîné par la suite des complications d'ordre sociologique et économique. De fait, la réduction des zones en eau provoque une diminution des sites exploitables et l'émergence de conflits entre villages ou familles pour l'accès à la ressource. Par ailleurs, un certain relâchement du contrôle des autorités traditionnelles lié à un accroissement démographique important aurait provoqué une augmentation du nombre de pêcheurs en vingt ans de l'ordre de 20 000 personnes (43 000 en 1966 contre 63 000 en 1989) conduisant à un partage difficile des captures par ailleurs en baisse.