Aneuploidy has been previously reported in wild and cultivated Pacific oysters, Crassostrea gigas, and has been shown to be negatively correlated with growth. This is especially important since high variability of growth rate is one of the major problems in the aquacultural production of this species. The existence of a genetic basis for the observed differences in aneuploidy was first investigated through the comparative study of six full-sib families, with mean individual weights ranging from 0.59 to 1.49 g. The slowest growing family was found to have the highest level of aneuploidy. Significant differences in aneuploidy were also found among families when individuals with the same growth rate were sampled. This supports the hypothesis of the existence of a genetic basis for the control of aneuploidy level. Additionally, the possible inheritance of the level of aneuploidy was studied in four full-sib progenies originating from crosses within and between two different populations with contrasting levels of aneuploidy. The limited number of parental oysters (N = 6) in which the scoring of aneuploidy was possible did not allow demonstration of the inheritance of the level of aneuploidy. However, a genetic difference in aneuploidy could be attributed to the origin of the parental populations. As in the first experiment, significant differences in aneuploidy were observed between progenies when sampling individuals of the same weight. Thus, the results of our study of full-sib progenies of C. gigas lend support to the hypothesis of a genetic basis for the level of aneuploidy.

Sturgeon production in Western Europe originating from aquaculture in 1999 was approximately 1300 t revealing an increasing trend. Three species represent 95 % of the annual production: white sturgeon (Acipenser transmontanus) 43 %, Siberian sturgeon (Acipenser baerii) 34 %, and Adriatic sturgeon (Acipenser naccarii) 18 %. The remainder is provided by various species including hybrids. The main countries in decreasing order of production are Italy, France, Spain, Germany and Poland. Fish are fed commercial formulated diet. The most significant changes in the sturgeon industry during recent years have been in the ownership of farms, in the emergence of the pond as a production system, and in the increasing caviar production from farmed sturgeon. In 1999, the production of farmed caviar from France and Italy, originating from Siberian and white sturgeon, respectively was close to 6 t. The number of active sturgeon farms in Western Europe is estimated to be approximately thirty, half of which are hatcheries. This paper presents different strategies and management approaches in sturgeon production and caviar processing. The potential caviar market and its dynamics are assessed and likely changes are discussed. Finally, some of the scientific investigations needed to improve and support this development are highlighted. Five different fields are distinguished: biological reserve, genetics, reproduction, farming, and quality of end products.

Several studies have found that, since 1975 at least, the atoll lagoon of Takapoto exhibits high salinities and high planktonic chlorophyll concentrations. We used observations gathered in Takapoto and 23 other atoll lagoons between 1995 and 2000 to study the water renewal rate (determined by different approaches) of Takapoto relative to that of the other lagoons. This rate is controlled by reef rim aperture, which is abnormally low in Takapoto. Across this set of lagoons, average water residence time was correlated with salinity, and with two descriptors of water column biological properties, chlorophyll and dissolved organic matter contents. In parallel to these bulk quantitative variations, qualitative variations were found inside this trophy gradient, concerning the size of primary producers (proportion of cells > 2.7 μm) and the composition of seston (relative phosphorus content). Takapoto Lagoon fits into a gradient of water residence time that controls the overall trophic web organization.

The distribution and population structure of the red shrimp, Aristeus antennatus, were investigated for an unexploited fishing ground in the Greek Ionian Sea (middle-eastern Mediterranean). A total of 8618 specimens, 7273 females and 1345 males was caught during a 12-month survey, from January to December 1997, at depths ranging from 400 to 800 m. Monthly size frequency distributions were analysed using different techniques, resulting in estimates of growth and mortality. Carapace lengths (cephalothoracic lengths, CL) ranged between 12 and 62 mm for females and 9 and 45 mm for males. The mean size of specimens exhibited statistically significant differences in relation to sex and months. Recruitment of both sexes occurred in mid-winter (January). Only the mean size of females seemed to increase with depth. Estimation of the von Bertalanffy growth parameters revealed high k values and a life expectancy of 4 and 5 years for males and females, respectively. A high percentage of specimens bore spermatophores during May and August, indicating that these months were peak breeding periods. Natural mortality rates ranged from 0.55 to 0.70 for females and from 0.62 to 0.79 for males, depending on the method used. Based on its biology and population dynamics, it appears that the red shrimp population in the study area has the potential to support a viable fishery.

The quality of Moroccan Atlantic coastal wasters was monitored from 1993 to 1997 by measuring hydrological parameters (dissolved oxygen, suspended particulate matter, phosphates, and nitrates), and using the mussel Mytilus galloprovincialis as a quantitative bioindicator of cadmium, copper, manganese, and zinc contamination. Mean concentrations of dissolved oxygen and suspended particulate matter were indicative of the effects of urban and industrial discharges of wastewater, particularly at Mohammedia, Casablanca, Mehdiya, Jorf Lasfar and Safi. Stations receiving urban wastewater showed high nitrate concentrations, especially at Mehdiya, Rabat, Mohammedia, Casablanca and El Jadida. Metal concentrations in mussels showed significant variations depending on the station and sampling period. Jorf Lasfar and Safi had the highest mean concentrations for cadmium (8 and 7 μg·g–1 dry weight respectively) and copper (74 and 25 μg·g–1 dry weight). The relation between cadmium concentrations in mussels, and phosphate concentrations in water suggests that the processing of phosphate ores at these two sites is responsible for contamination. Mussels in the Mohammedia–Casablanca sector had the highest zinc concentrations (338–379 μg·g–1 dry weight), followed by those collected at Jorf Lasfar (267 μg·g–1 dry weight), and Sidi Moussa and Safi (290–301 μg·g–1 dry weight). The distribution of manganese concentrations, which were maximal in estuaries (up to 19 μg·g–1 dry weight), was indicative of terrigenous inputs. Seasonal variations in mussel metal concentrations were characterised by winter minima, and apparently related to the physiological cycle of the animal. With the exception of cadmium-contaminated areas, the quality of mussels on the Moroccan Atlantic coast is good with respect to food safety standards.

The Eastern Channel (ICES division 7d) is considered a unit for stock management of the common sole Solea solea and the plaice Pleuronectes platessa. At this scale, the aim of this work is to model the juvenile distribution of these flatfish. The database used, based on different surveys undertaken during the two last decades, includes 4500 coastal beam trawl hauls throughout the Eastern Channel coasts. Multivariate analyses are used to study the interannual fluctuations in flatfish recruitment of the region. This approach allows us to separate the Eastern Channel into homogeneous sectors with regard to these fluctuations. The physical parameters that contribute to the observed juvenile sole and plaice distributions are identified and their distributions are modelled using generalized linear models. The results of these models, and the areas of the different populations derived from a geographic information system, are used to identify the main nursery grounds and to compare their respective importance. This quantitative approach identifies the lack of estuarine dependence of the nursery grounds, and highlights those areas where anthropogenic disturbance could influence these populations.

Brown trout (Salmo trutta) were selected for growth for 4 generations. We tested the effects of selection on voluntary feed intake measured by self-feeders, feed efficiency and size variability. The specific effects of a slight feed restriction and of food deprivation were also investigated. Fish were issued from groups of eggs of selected females fertilised with sperm of selected (S group) or control males (S1/2 group). According to the growth rates expected for the selected and control lines, the S1/2 group was fertilised 12 days before the S group, so that all the fish reached 8 g at the same time. At 8 g, they were allotted to 8 tanks (500 fish per group) and 3 experimental periods followed. Fish were accustomed to self-feeders during a 28 days pre-experimental period. Then, half of the groups were fed ad libitum, and half were restricted (80% of the expected ad libitum level) for 171 days; growth and feed intake were recorded regularly and any uneaten food was weighed. Then followed a 56 days starvation period. At the end of the pre-experimental, feeding and starvation periods, individual weights and lengths were measured on 50 trout per tank. The response to selection at the end of the feeding period varied with the feeding level. In ad libitum fed groups, the mean final body weight of S was +6.1% higher than that of S1/2 and feed efficiency was similar (1.10 for S and S1/2). The higher growth of S compared to S1/2 was related to a higher feed intake of the S groups (+5.3%). When fish were restricted, the final body weight was lower in S (117.1 ± 2.1 g) than in S1/2 groups (123.8 ± 1.7 g). This was mainly related to a slightly lower feed efficiency of S compared to S1/2 at the beginning of the feeding period. Neither the group nor the feeding level affected the size variability of the fish. At the end of the starvation period, the relative loss of weight was equivalent for all the groups, and the variability of the weight was higher for S than for S1/2. The results highlight the fact that genetic gain can only be expressed when brown trout are fed ad libitum.

A programme of zoosanitary survey of the populations of black-lip pearl oyster (P. margaritifera) has been developed in French Polynesia during 1996 and 1997. Based on histological and ultrastructural examinations, the study of pearl oysters sampled in several pearl farms from the Society Islands, Tuamotu Atolls and Gambier Archipelago, has been particularly turned to enzootic pathological problems. Particular attention has been given to the shell disease and to the necrosis of the adductor muscle, symptoms that had accompanied the mass mortality in 1985.Virus–like particles, about 40 nm in diameter, were detected in membrane bound vesicles from the necrosized muscle tissue. A new Rickettsia-like organism found in epithelial cells of the digestive tubules was described, while parasites previously reported, such as cestodes and gregarines, were recognized in some animals. Apart from the pathology, a thorough study of ‘parasite-like bodies’ discovered in the pearl sack epithelium showed dysfunction in the periostracal secretion.

Culture of sturgeons in Russia began in the second half of the 19th century. During the first part of the 20th century, a significant research effort was devoted to the control of reproduction and the rearing of larvae mostly for stock enhancement purpose in rivers. Large-scale construction of hatcheries began in the 1950s after the damming of rivers, and by the 1980s over 130 million 1–3-g juveniles per year were being produced from wild broodstock. Presently, the production is 100 million juveniles. Emphasis is now on optimising stocking results through consideration of fish-specific factors (e.g. behaviour, fitness, size, balance between species) as well as environmental variables (food availability, release sites, salinity, precipitation regime). Food fish production of sturgeon (market size is 1.5–2.0 kg is just beginning using captive broodstock and new growing technologies. In 2000, farm production was about 1650 t, which was higher than sturgeon landing from wild fisheries (1500 t declared in 2000).

A total of 361 skipjack tuna (Katsuwonus pelamis) between 41.5 and 71.5 cm fork length and 333 yellowfin tuna (Thunnus albacares) between 48 and 150 cm fork length were collected in the western Indian ocean, between latitude 5° N to 10° S and longitude 45° to 65° E from February 1989 to November 1990. Yellowfin populations have one major reproductive season during the north monsoon while in skipjack the reproduction is almost continuous all year round with two peaks in activity during north and south monsoons. The gonadosomatic indexes (GSI) are correlated with the three climatic situations: the north monsoon, the south monsoon and two inter-monsoon seasons. The steroid hormone variations (oestradiol, oestrone and testosterone) are well correlated with the GSI in females. In males, maximum levels coincided with the two main reproduction periods in skipjack while the maximum values of testosterone and 11-ketotestosterone levels were only found during the north monsoon. Even if both species are continuous spawners, these results indicate the existence of different reproductive traits, especially when considering steroidogenesis and vitellogenesis. These findings suggest that over our fishing zone, the reproductive activity is significantly modulated by climatic changes.

Cinq mille larves de poisson-spatule Polyodon spathula agées de 3–4 jours, en provenance du Missouri aux États-Unis, ont été introduites dans l’ex-URSS, en 1974 dans le cadre des accords de coopération scientifique entre les deux pays. Cette première tentative n’a été que partiellement réussie ; seuls quelques survivants ont atteint 600–900 g après 2 ans puis la maturité sexuelle et se sont reproduits en 1984 et 1986. L’élevage de cette espèce étant apparu possible, de nouvelles introductions ont eu lieu, l’une en 1976, qui fut sans succès et une autre en 1977, réparties dans deux écloseries (Goreachi Cluch et Krasnodar-Ikreanoe). En 1978, une centaine des spécimens de Goreachi Cluch ont été exportés en Moldavie et élevés en polyculture dans plusieurs piscicultures où la reproduction de trois femelles a été obtenue en 1988 et 1989. Des juvéniles issus de ces reproductions ont été exportés en URSS (Ikreanoe) et en Roumanie et Hongrie. Par ailleurs, la station de recherches de Nucet en Roumanie a importé des larves de poisson-spatule des États-Unis en 1992, 1993 et 1994 (environ 2000 larves à chaque introduction). Dans ces différents pays, des recherches ont été conduites sur cette espèce. Actuellement, la production commerciale a débuté en Russie et Moldavie pour la chair, et il a été montré, dans le cadre d’un projet CE Copernicus, qu’il était possible de produire du caviar. P. spathula peut venir en complément ou en substitution partielle de carpes, en polyculture et a une valeur commerciale plus élevée. Le problème est que la seconde génération présente en Russie, Moldavie, Roumanie, et peut être en Hongrie, est dérivée d’un nombre limité de parents, avec des risques de perte de variabilité génétique.

Because preying on close relatives may cause a loss of inclusive fitness, cannibalistic animals are generally deemed to cannibalise non-related conspecifics preferentially to kins. Whether this basic principle also applies to fish exerting intracohort cannibalism at an early developmental stage is uncertain, and more intense cannibalism among mixed progenies might just be a consequence of greater size heterogeneity. To investigate this, progenies of sharptooth catfish of equivalent initial body weights but with contrasting size heterogeneity were reared separately or in mixed groups containing equal proportions of each progeny (27 ± 1°C, 12 h light:12 h night, 2.5 L aquaria, 100 or 200 fish·L–1). Cannibalism was monitored on a daily basis until the end of the larval stage (3–15 days after hatching). Cannibalism in mixed groups was intermediate between those in pure progenies, and was positively correlated (R2 = 0.803, P < 0.01) with initial size heterogeneity, irrespectively of fish origin. This finding does not exclude that catfish larvae were able to discriminate between siblings and non-related fish, but this obviously had very little influence on cannibalism. The implications of this finding are discussed, as they apply to prey selection in fast growing larvae, and aquaculture of catfish.

L'affinage traditionnel des huîtres creuses, pratiqué dans lesclaires ostréicoles de la façade Atlantique française, est soumis auxfluctuations des facteurs environnementaux. Un procédé d'affinagecontrôlé en terme de matières organique et inorganique particulaires(MOP et MIP) et de température a étédéveloppé afin de réduire la variabilité de croissance de lachair des huîtres. Cet élevage intensif repose sur la production de ladiatomée Skeletonema costatum, distribuée aux huîtres avecune concentration moyenne de 4–5 mg deMOP·L–1. Un modèle écophysiologique del'huître Crassostrea gigas, simulant les croissances du soma et desréserves–gonades, a été appliqué aux conditions d'affinagecontrôlé dans le but d'analyser les réponses du bivalve. Sonélaboration a nécessité un retour à l'expérimentation. Deuxfonctions d'alimentation ont été étudiées au laboratoire : lafiltration et la production de pseudofèces, intervenant dans la régulationde l'ingestion. Les résultats, pour une température de 14 °C, etpour une gamme de MOP et de MIP variant respectivement de 4 à18 mg·L–1 et de 15 à55 mg·L–1, montrent que l'ingestion est réguléepar la production de pseudofèces, la filtration ne présentant pas devariation significative (moyenne de2,09 ± 0,11 L·h–1·g–1, avec un taux d'activité de 59%). Cette production de pseudofèces, quiengendre une augmentation de la fraction organique ingérée par lemécanisme de sélection pré-ingestive, permet de compenser lavariabilité des concentrations en MIP. Des simulations ont permisd’analyser les effets négatifs de ce facteur environnemental sur lacroissance du bivalve. Il apparaît alors que la ration utilisée en affinagecontrôlé (4–5 mg de MOP.L–1) permet unecroissance en chair sèche malgré des concentrations simuléesatteignant 50 mg·L–1 de MIP. Lors del'élaboration du modèle pour les conditions spécifiques àl'affinage contrôlé, la gamétogenèse est apparue comme unprocessus déterminant pour la répartition de l'énergie chez lebivalve.

Small-scale fish farming in tropical Africa is mainly based on pond culture of Nile tilapia Oreochromis niloticus with supplementary organic fertilisation. Until recently, the ‘high’ stocking densities practised (2 fish·m–2) led to stunted populations and very low yields. Since 1996, rural fish farming developed significantly in Côte d’Ivoire. Only a dramatic decrease in stocking densities allowed fish farmers to produce marketable-sized tilapia with reasonable yield in extensive culture. Density control is achieved through tilapia monosex male culture and stocking the predator Hemichromis fasciatus. Further development of low-input tilapia farming requires improvement of production results. A growth model based on maximal growth and ingestion, maintenance needs and efficiency of food for growth was developed to explain and help optimise production results. The model was validated with farm and experimental data and demonstrated that, for a given rearing period (from 30–50 g fingerling, to market-size), yield increased with density, but then decreased beyond an optimal density. When market-weight target is set, the same variation of yield according to stocking density is observed. Densities of 2 to 3 fish·m–2 markedly reduce tilapia yield in extensive culture. Moreover, increasing market weight from 150 to 450 g·fish–1 will only induce a limited decrease in maximal yield (around 20 %) if the density is lowered and the rearing period lengthened. This decrease is more than compensated by the higher price of large tilapia. Using rearing cycle data, the model can predict the results of alternate combinations of stocking density and duration of rearing period under the same pond management. Thus, production results can be optimised given the objectives and constraints of each fish farmer. This model is a valuable tool to develop extensive tilapia farming in tropical areas, and raises questions for researchers.

A total of ten Heptranchias perlo, eight Deania histricosa, two D. calcea, and two D. profundorum from the Great Meteor Bank, central East Atlantic, were studied for cestodes. The elasmobranchs were caught using bottom trawl or long-lines during September 1998 in 298–1075 m water depth. Seven different cestode species were found: Tentacularia coryphaenae, Deanicola minor, D. protentus, Grillotia meteori sp. nov., Grillotia cf. microthrix (Trypanorhyncha), Crossobothrium dohrnii, and Crossobothrium sp. (Tetraphyllidea). T. coryphaenae occurred encapsulated in the stomach wall and all other species were found within the host intestine. G. meteori sp. nov. and G. cf. microthrix additionally infested the musculature as well as the stomach and intestinal wall. D. profundorum harboured five different cestode species and D. histricosa, H. perlo, and D. calcea were infested with four, three and two species, respectively. With 332 and 181 specimens, D. minor and G. cf. microthrix were the most abundant cestodes. Grillotia meteori sp. nov., Crossobothrium sp., and C. dohrnii were host specific for Deania profundorum, D. histricosa and H. perlo, respectively. The other species were found in more than one elasmobranch, with Deanicola minor and D. protentus restricted to Deania sp. Most parasites are recorded for the first time from the central East Atlantic around the Great Meteor Bank.

Retention of the second polar body for the production of triploid Arctic charr (Salvelinus alpinus) was induced by 65 MPa (650 bar) pressure shocks applied 30, 40 or 50 min after fertilization, each shock lasting 5 min. Triploid yield (percentage of relative survival to control × percent triploidy) varied from 55 to 100 % and it was generally superior to 80. Despite increased mortality and decreased growth in diploid charrs during the spawning period, growth and survival did not differ between diploid and triploid Arctic charr up to and during their third year of life. Most of the triploid males had developed testis, but they did not render milt; few triploid females had developed ovaries. Fecundity of triploid females was low and fertilized eggs from triploid females did not hatch.

The food utilisation and partitioning between three age-groups of Atlantic salmon parr were studied in the subarctic river Tana (70° N, 27° E) by analysis of fish stomach contents and invertebrate composition in the three main lotic feeding habitats: bottom substratum, water column and surface. The salmon parr exhibited large seasonal variation in their food choice, but the different age-groups had a similar diet, dominated by mayfly and stonefly nymphs in May, flying insects and simuliid larvae and pupae in July, and caddis fly larvae in August and September. Some differences in the food resource use of the three age-groups were however also observed, mainly related to size-dependent differences in feeding abilities, but partly also to different use of feeding habitats. Small-sized stonefly and mayfly nymphs and simuliid larvae and pupae decreased in importance with increasing fish age, whereas Trichoptera larvae and flying insects increased. The low resource partitioning between the different age-groups of salmon parr suggests that intraspecific competition for food may occur. All age-groups mostly fed on prey types associated with the bottom habitat, and substantial drift feeding was only observed in July, probably due to low drift rates throughout most of the summer season in this subarctic river.

The reproductive characteristics of Oreochromis niloticus, a multiple spawner, have been compared between populations submitted experimentally to three types of spatial structure. Fish from a same original stock were divided and reared for 2 months in: 1) concrete tanks with a bare bottom, 2) concrete tanks with a sandy bottom, or 3) concrete tanks equipped with an artificial reef. The females were then killed and their gonads examined for sexual stage and fecundity determination. Fecundity was inversely correlated to the spatial complexity of the environment whereas oocyte size tented to increase together with spatial complexity. Females placed in tanks with artificial reefs presented a lower fecundity and reproductive investment and bigger oocytes than those maintained in the bare bottom tanks. Fish reared in tanks with a sandy bottom had intermediate reproductive traits. The response of females to changes in the spatial structure of their environment was observed after only one or two reproductive cycles, providing the first experimental evidence of such rapid phenotypic adaptation to environmental complexity. The results also indicate that the perception of living space, arising from the availability of refuges and spawning sites, is more likely to influence the reproduction of tilapias than substrate quality.

Paddlefish are endemic to most rivers and tributaries of the Mississippi basin and are found in 22 states of the United States. In 1989, US Fish and Wildlife Service (USFWS) listed paddlefish as a category 2 species because data were lacking on its population status. In 1992, USFWS added paddlefish to the list of Appendix II of the Convention on International trade in Endangered Species of Wild Fauna and Flora (CITES) primarily due to concerns about illegal poaching in the international caviar trade. Therefore, paddlefish aquaculture will provide alternative fish sources for the marketplace in the era of strict federal and state regulations on wild populations. Aquaculture of paddlefish is in a research and developmental phase. Most broodstock are obtained from wild sources, though some mature fish have been developed in captivity. Artificial propagation techniques are resulting in > 80 % egg fertility. Larval paddlefish are initially raised in organically fertilized, zooplankton-rich (i.e. Daphnia sp.) ponds, and then trained on extruded trout/salmon diets until the juvenile fish are > 30 cm in total length. Tank culture is also an alternative for raising juvenile fish. Juvenile paddlefish, a filter feeder that requires zooplankton as its primary food, are being grown in reservoirs and in polyculture with channel catfish (Ictalurus punctatus) in Kentucky, Indiana, Missouri and Alabama. Production yields are 200–400 kg·ha–1 in polyculture and in reservoirs ranching resulted in 55–175 kg·ha–1. Reservoir ranching is ideal for caviar production; whereas, paddlefish (1.5 to 4.0 kg) cultured with catfish is for meat production. A system to produce all-female progeny through artificial propagation with sex-inverted, gynogenetic broodstock and attempting to develop optimal cryopreservation techniques for the milt of these unique broodstock is currently being tested. Value-added products such as hot and cold smoked paddlefish are the major effort being developed for the marketplace. Consumer acceptability of value-added products from paddlefish has been better than channel catfish.

Changes in the total amino acid (TAA) and the free amino acid (FAA) contents during embryonic development, through newly spawned eggs, to pre-settled larvae of blacklip abalone (Haliotis rubra) are described. The TAA (protein bound + free) and the FAA contents increased prior to hatching but decreased towards settlement, but the changes were not always significant between different stages of development. Threonine, arginine, lysine and leucine accounted for nearly 50 % of the total essential amino acids (TEAA) in all developmental stages. The mean FAA content of newly spawned eggs was 262.8 ± 28.2 pmol·ind–1 and accounted for 11.5 ± 8.3 % of the TAA. Free essential amino acid (FEAA) content increased significantly as development progressed (P < 0.05), in which threonine, arginine and lysine accounted for over 63 % of this pool. In all developmental stages, the FAA pool was dominated by the non-essential amino acids taurine + proline which accounted for 79.5 % of the total. Generally, the FAA accounted for between 10 to 15 % of the TAA in the different developmental stages of blacklip abalone. All evidence appears to indicate that in blacklip abalone the energy requirements during early ontogeny are mostly met with from the lipid reserves, and that there is a tendency to conserve amino acids until pre-settlement.