Catch-per-unit effort (CPUE) has frequently been used as an index of abundance and more specifically to calibrate virtual population analysis (VPA). In multi-species fisheries, CPUE calculated from fishing trips targeting the species seems to be more effective for calibration than the classical ratio total landings/total effort. Target species are determined from an analysis of the composition of catches (landings) of each fishing trip, each trip being categorised as to whether it targets the given species or not. It is obvious that existing but not reported discards would affect these results. Classification of trips can be achieved on a single-species basis, each species being considered successively and each trip possibly being relevant for more than one species. Using a more general approach, classification can be achieved by métiers, each of these being determined by one or a group of target species and each trip being categorised into one and only one métier. This method of categorising trips is based on thresholds of target species contribution to the catch and on an overall explanatory level. For the main species of the French demersal fishery off the west coast of Scotland and in the Celtic Sea, CPUEs are calculated using different methods to define the trips used to calculate fishing effort and associated landings. Besides important differences in actual values, CPUEs may also differ in their trends depending on the definition of directed effort. Tuned VPA, carried out for some species, shows that large variations in population estimates, fishing mortality or short-term predictions could occur when using directed effort, while the catchability model fits the data better.

Large differences in reproductive traits were observed between populations of Oreochromis niloticus sampled in 9 manmade lakes of Ivory Coast. In order to assess whether these variations in reproductive characteristics resulted from short term adaptation or from a longer evolutionary process, living specimens were caught in the two most differentiated populations in term of life history traits, and placed in a common environment in culture conditions. Genetic analysis of fish from these two populations were performed using four microsatellite markers and revealed that both descended originally from the same strain (Bouaké station) which was constituted from broodfish initially caught in the Nile and Volta basins. Fish from the two populations were subjected to a common environment (pond and aquariums) for five months. Then, their reproductive characteristics were analysed and no significant differences were found in fecundity, egg size and spawning frequency. These results indicate that reproductive differences between the two populations, originally observed in the two reservoirs, mostly reflect the phenotypic plasticity of the species in facing different environmental conditions.

L'inversion hormonale du sexe chez Oreochromis aureus (génotype mâle ZZ et génotype femelle ZW) avec un œstrogène (1717α-éthynylœstradiol) conduit à l'obtention de pseudofemelles, caractérisées par un genotype mâle (ZZ). Le croisement de ces pseudofemelles avec des mâles (ZZ) donne, en théorie, des populations 100 % mâles. Nous avons déterminé et comparé les principaux paramètres caractéristiques de la reproduction au sein de trois groupes de géniteurs O. aureus. Le premier groupe (groupe 1) est composé de femelles, le second (groupe 2) de pseudofemelles et le troisième (groupe 3) de femelles et de pseudofemelles. La fécondité et le poids des œufs des femelles et des pseudofemelles ne sont pas significativement différents. Dans le groupe 3, le taux de reproduction des pseudofemelles (0,6 pontes) est plus faible que celui des femelles (6,4 pontes). Dans ce groupe 60 % des pseudo-femelles ne se sont jamais reproduites. Dans les groupes 1 et 2, il n'existe pas de différence entre les femelles (6,9 pontes) et les pseudofemelles (4,7 pontes). Le plus faible taux de reproduction des pseudofemelles pourrait résulter de l'expression du génotype sexuel mâle chez ces individus.

Nicotine injected intravenously or on pituitary in vivo stimulated maturational gonadotropin (GtH2) secretion in domperidone (D-2 receptor antagonist) pretreated carps. The effective dose was 1 mg·kg−1 and 100 μg·kg−1, respectively. No stimulatory effects of nicotine were observed in normal (non-treated) carps. When nicotine was injected together with gonadotropin releasing hormone (GnRH) analogs (D-Arg6 sGnRH or D-Ala6 LHRH) a clear potentiation effect of nicotine on GnRH analogs' action was observed. This potentiation was seen even in normal fish where nicotine itself had no effect on GtH2 release. A synergism between nicotine and GnRH analogs appeared when low doses of GnRH analogs were used. In domperidone pretreated fish, this synergism occurred after injection of 1 μg·kg−1 of sGnRHa. In normal fish, the same phenomenon was observed after injection of 5 μg·kg−1 of sGnRHa or 20 μg·kg−1 of LHRHa. Higher doses of GnRH analogs mask this effect. Results confirm previous in vitro findings on the stimulatory action of nicotine on GtH2 secretion. They also indicate a possible synergy between nicotine and GnRH as well as an inhibitory influence of dopamine on nicotine's action.

Improved inland culturing methods for marine invertebrates are the most important prerequisite for the establishment of inbred lines. Here, we study the effects of improved diet on growth rates, survivorship and reproductive activities of the colonial urochordate Botryllus schlosseri, an important model species in a variety of scientific disciplines. Six long-term experiments (6−8 weeks each; 3−8 treatments per experiment) were conducted in an attempt to evaluate 10 different food types alone and in various combinations. We took a hierarchical approach in which some food types were contrasted and the results were used to design the next experimental set with new food types. A mixture of at least two types of diets was superior to any monotonous diet examined. Results were also characterized by high variability between colonies of the same hatch in any studied life history aspect, by the appearance of reproductive sterile colonies in the cultures, high survivorship, fast growing and long-lived colonies. The improved maintenance protocols enabled us to develop the first long-lived (> 6.5 years) inbred line of Botryllus with four successive generations of self-crossed pedigree animals.

The most distinctive feature of the reproductive biology of Hoplosternum littorale is the building and guarding of an elaborate floating bubble nest. Reproduction starts at the age of one year. Males grow to a larger size than females and, during the breeding season, they develop fat deposits in the pectoral fin and an elongated recurved pectoral spine that often assumes a reddish colour. Analysis of gonadal development and surveys of nesting in swamps show that initiation of reproduction is associated with the onset of the rainy season. Males start building the nest at night, and spawning takes place around noon the day after. Most nests are built in newly flooded swamps, especially in open water in the peripheral area of the swamp. A minimum distance of 10 m between nests is usually observed. The floating bubble nest consists of a dome of plant material supported by oxygen-rich foam produced by the male. Diameter and height of the nest average 30 and 6 cm, respectively. The nest is the centre of a territory that is vigorously defended by the male, using its enlarged pectoral spine, against conspecific and heterospecific intruders. The number of nests that did not acquire spawns (48 %) suggests a bold competition among males for females. There are indications that the female drinks the sperm and that fertilization takes place after the sperm has passed through her digestive tract. Hoplosternum littorale is a multiple spawner. Investment in reproduction is high in females since they can spawn up to 14 times during a 7-month breeding season and each spawn consists of 6 000 to 9 000 eggs. On average, two to four females spawn simultaneously, resulting in an average number of 20 000 eggs per nest. Incubation of the eggs takes two to three days depending on the temperature in the nest. Despite intense predation pressure on eggs and larvae, the guarding behaviour of the male extends for only one or two days after hatching. In the hypoxic water of tropical swamps, the main function of the floating bubble nest appears to be to provide oxygen to the developing eggs by lifting the eggs above the water surface while protecting them from desiccation. Other functions of the nest may be protection of the brood against predators, temperature regulation, identification of the centre of the territory and synchronization of reproductive activities. We suggest that H. littorale may be a useful model for the study of the reproduction of tropical freshwater fish in hypoxic environments.

A number of feedstuffs was tested to obtain the apparent digestibility coefficients (ADC) of dry matter, protein, energy and phosphorus for seabass juveniles (individual mean weight of 40 g). The effect of the inclusion level (15 and 30 %) of a feedstuff in a reference diet on the ADC was also evaluated. The feedstuffs tested in this trial were two fish meals, a fish protein hydrolysate, blood meal, meat meal, soybean meal and yellow dextrin. The ADC of dry matter were consistently lower than those of energy, but there was a significant positive correlation between them. The ADC of protein were high (range 89−97 %) in all feedstuffs. The ADC of energy of animal feedstuffs (range 86−96 %) and dextrin (93 %) were also high, while that of soybean was lower (70 %). The ADC of phosphorus of animal feedstuffs averaged 81 % whereas that of soybean was only 38 %. There were no significant differences in the ADC of protein and energy of each feedstuff at the two inclusion levels tested.