The rapid development of the albacore tuna (Thunnus alalunga) driftnet fishery in the Bay of Biscay (Atlantic ocean, France) has incited European management authorities to ask for a study of its ecological impact on populations of common dolphins and striped dolphins. A programme with onboard observers has been led during 1992 and 1993, and a sighting survey has allowed the evaluation of the abundances of fractions of populations in the studied area. For the population of common dolphins, the biological parameter estimation has allowed the building of a discrete age-structured model based on a Leslie matrix. Sensitivity studies have been conducted using four model parameters (age of first reproduction, interval between births, juvenile and adult survival rates. Results show that the increase rate of the population presents the highest sensitivity versus adult survival rate and, in second place versus the interval between births.

A longline ‘métier’ using small hooks for ‘red’ sea breams (Pagellus acarne and Pagellus erythrinus) in the Algarve (south of Portugal) was studied. Experimental longlining was carried out with three sizes of "Mustad" round bend, flatted, spade end Quality 2316 DT hooks (numbers 11, 13 and 15) and two types of bait: razor shell (Ensis siliqua) and mud shrimp (Upogebia pusilla). A total of 3 328 fish and at least 36 species were caught with 33 600 hooks fished in 28 longline sets. Five species of sea breams (Sparidae) accounted for 79% of the catch: Pagellus acarne, Pagellus erythrinus, Diplodus vulgaris, Spondyliosoma cantharus, and Boops boops. High catch rates of 20-30 fish per 100 hooks were made in a number of 1 200 hook longline sets, with total catch weights of 40 to more than 60 kg per set. In general, the smallest hook (number 15) had the highest catch rate. Bait type did not significantly affect the catch size distributions. Although more fish were caught with the razor shell bait, higher catch rates of ‘red’ sea breams were obtained with mud shrimp. Catch rates were also affected by the location of the fishing grounds and the time of the set, with the highest catch rates obtained when the longline was set within two hours before sunrise. A wide size range was caught for each species, with highly overlapped catch size frequency distributions for the three hook sizes used. Except for Spondyliosoma cantharus, few illegal-sized fish were caught, even with the smallest hook. The logistic model fitted by maximum likelihood was used to describe hook selectivity for Diplodus vulgaris, Pagellus acarne, Pagellus erythrinus, and Spondyliosoma cantharus.

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.

A model is used to explore whether local density-dependent recruitment relationships can be observed when considering a larger scale. A virtual population of spawners is tracked within an artificial environment composed of cells. Spawners can move from one cell to another on a spatial grid defined as a square lattice (lattice scale) made of 20 × 20 jointed hexagonal cells (local scale). Five spawner's behaviours are experimented successively: i) spawners stay in the same cell to spawn; ii) they move randomly towards one of the neighbouring cells; iii) they move towards the least populated neighbouring cell; iv) they move towards the most populated neighbouring cell; and v) they move randomly towards a neighbouring cell and then move towards the most populated neighbouring cell. When the migration of spawners is achieved, spawners reproduce only once, recruitment takes place and then they disappear. The recruitment is an event which occurs at a local scale: at the scale of the cell. Using Ricker's stock-recruitment relationship, in each cell the number of recruits is a function of the spawners. Random migrations and migrations towards the less populated cell allow a homogeneous distribution of the spawners throughout the lattice. Whereas in the three other cases, this distribution is not homogenised. The homogenisation of the lattice allows synchrony between local populations and then a stock-recruitment relationship is observable at the lattice scale. Simulations show that local density-dependence is not always detectable when considering large spatial scale. This result strengthens the idea that the choice of spatial scale is essential when studying stock-recruitment relationship.

A split-beam hydroacoustic system with automatic tracking of individual fish is being used to estimate the number of upstream migrating adult Pacific salmon in the Fraser River in British Columbia, Canada. To determine the bias and variance of the estimates of migrating fish numbers produced by this system, we compare simultaneous acoustic and visual estimates. These data demonstrate that, as fish densities increased, both a 4° × 10° and an 8° transducer produced lower estimates than the visual count. However, in the region of fish densities typically observed for migrating salmon, the 4° × 10° transducer estimates did not differ significantly from the visual count. A detailed description of the experimental configuration is given, including how the acoustic and video data were synchronized. Analyses of the data indicate that the size and shape of the acoustic beam has a pronounced effect on the bias of the acoustic estimates. In addition, the performance of the tracking software deteriorates as fish densities become very high.

The present work is based on a set of bottom trawl surveys performed in the Gulf of Lions between 1983 and 1992. A new method which couples the STATIS multitable approach with the logic of correspondence analysis (CoA) is proposed to study the stability of spatial organization of demersal assemblages in terms of species composition. This CoA version of STATIS has provided a clear representation of the stable part of the spatial structure of the assemblages. In addition, it gave an insight into the interannual variations of the distribution of each population around the reference structure. Our results showed that the demersal assemblages of the Gulf of Lions exhibited bold spatial structuring, mainly orientated along a bathymetric gradient. This gradient is structured around three major regions: the coast, the continental shelf and the continental slope. Despite sampling variations that occurred during the course of the study, the analysis showed a high degree of reproducibility for this spatial pattern. With the exception of Mullus surmuletus, the species considered in this investigation exhibit limited variations in their spatial distribution. Finally, in the absence of log-books covering the activities of commercial fishing vessels, these findings constitute a base of reference for the analysis of the dynamics of fishing fleets exploiting the demersal resources of the Gulf of Lions.

An adaptation of the von Bertalanffy growth model is formulated to describe the phenotypic plasticity of fish somatic growth in relation to trophic conditions. The model is developed for the North sea Downs herring (Clupea harengus). It suggests that annual growth variability during 1974-1990 was mainly due to the combined effects of herring abundance and wind-induced turbulence (coincident with the spring stratification of the water column). Springtime turbulences cause reduced and delayed planktonic blooms preceding the annual foraging period of Downs herring. The negative relation observed between herring abundance and growth is hypothesized to be due to intra-specific competition for trophic resources. Incorporated into the calculation of yield per recruit, the established growth model provides slightly more optimistic diagnoses while dropping the classic assumption of constant weight at age.

Feeding guides for salmonid fishes have been available from various sources for many years. These feeding guides have originated in one way or another from earlier feeding charts of the 1950-60s when meal-meat mixture diets were widely used. Few of the feeding guides available today are based on actual bioenergetics data at different water temperatures and are adapted to high energy diets. New feeding standards have been developed based on principles of nutritional energetics in which the digestible energy content of diet, digestible protein and energy ratio and the amount of digestible energy required per unit of live weight gain are taken into account. The gain expressed as retained energy in carcass and maintenance energy at different water temperatures is the main criteria for energy and feed allocations. Series of bioenergetic models were developed based on these principles and a stand-alone multimedia program was written to facilitate computation of the models. This program predicts growth and energy, nitrogen and phosphorus retention, requirements and excretions to determine feeding standards, waste outputs and effluent water quality based on a biological method. The models require initial and final body weights, water temperature, growth coefficient, carcass energy content and waste coefficients to estimate input and output. Accurate determinations of the thermal-unit growth coefficient, apparent digestibility coefficients and retention efficiencies are essential and these coefficients are determined by biological experiments in the laboratory and field. Oxygen requirement is included to aid environmental control in fish culture system. The Fish-PrFEQ program also contains modules for production records, performance calculations and data base management for input and output data which may be exported for further data and graphic manipulations.

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.

Eggs from three distinct populations of walleye Stizostedion vitreum, one domesticated (London State Fish Hatchery) and two wild (Lake Erie and Salt Fork Reservoir), were compared in terms of total lipid content and fatty acid profiles (phospholipids and neutral lipids). The concentrations of total lipids in eggs from domesticated broodstock were significantly lower (8.6 ± 1.0 % of wet weight) than those of both wild populations (13.3 ± 0.9 % and 10.9 ± 0.6 % of wet weight for Lake Erie and Salt Fork Reservoir, respectively). The profiles of fatty acids in egg lipids differed significantly among the three investigated populations. Domesticated females fed a formulated diet produced eggs containing significantly higher levels of linoleic acid (18:2n-6), characteristic of plant lipids. However, arachidonic acid (20:4n-6), was at significantly higher levels in eggs of wild walleye stocks. Although eicosapentaenoic acid (20:5n-3) was detected at significantly higher levels in eggs from Lake Erie walleye, docosahexaenoic acid (22:6n-3), the most abundant in polar lipids, was found at similar levels in eggs of all three populations. Survival of walleye embryos was correlated with the concentrations of polyunsaturated long chain fatty acids. Our data suggest that deficiency in n-3 fatty acids might be associated with impaired development of walleye, and thus poor larval and juvenile viability.

In order to manage the fish stock of the Senegal coastal zone it is necessary to carry out direct assessment surveys by acoustic methods. Acoustic surveys were carried out in this region from a sports-fishing boat, using a split-beam echo sounder in vertical mode, in areas with depth less than 15 m. On a short time scale, spatial structure of the fish population remained stable. The average acoustic biomass detected was variable, but we observed a relative stability of target strength distribution of single fish. The use of acoustic methods in these areas of shallow depths, the consequences of escape behaviour of the fish, and sampling strategies are discussed.

Brown trout and rainbow trout (average weight 100 g) were reared in fresh water at 12 °C under the same conditions before transferring brown trout to sea water, in order to compare phosphorus utilisation in both species. Apparent phosphorus availability, orthophosphate excretion and phosphorus accretion in the fish were directly determined. Thus, actual phosphorus mass balance was built. Rainbow trout raised in fresh water had a higher phosphorus retention coefficient (maximum 50 %) than brown trout reared in fresh water (maximum 45 %). Transferring brown trout to sea water induced a reduction in phosphorus retention (maximum 39 %). Orthophosphate excretion, ranging 7-20 mg phosphorus per kg wet weight per day, represented 10-20 % of ingested phosphorus. Phosphorus availability was lower in brown trout raised in sea water (65 %) than brown trout raised in fresh water (76 %). Phosphorus balance measurements showed that 90 to 98 % of phosphorus flow could be accounted for.

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.

This work studied some of the metabolic responses of Nephrops norvegicus to a progressive reduction in water oxygen tension (PwO2) at 12 °C. Experiments were designed to simulate water quality conditions that may occur during the trade of live crustaceans. Oxygen consumption rates and ammonia efflux rates were found to be constant over a wide range of PwO2 values (20.4-5.9 kPa). A similar result was found for the difference between post-branchial and pre-branchial oxygen concentrations (20.4-2.6 kPa), obtained from a separate experiment. Anaerobic pathways, however, were activated after PwO2 reached 6.3 kPa, as blood lactate and glucose concentrations increased from 1.24 ± 0.08 and 1.17 ± 0.19 (T0 values) to 10.55 ± 8.99 and 3.63 ± 0.89 mg · 100 mL−1 respectively. N. norvegicus was able to maintain blood pH levels at relatively constant values despite a drop in water pH levels and the accumulation of lactate observed at low PwO2. Heart rates also remained stable during PwO2 reductions, but scaphognathite beat rate increased considerably, probably as an attempt to maintain steady weight-specific oxygen consumption rates. N. norvegicus appeared to be well adapted to cope with progressive hypoxia as may occur during holding and transportation procedures.

The fatty acid profile of the galaxiid fish Galaxias maculatus (Salmoniformes) collected from an estuarine habitat (a river mouth), a freshwater creek and two land-locked freshwater lakes in Victoria, Australia, were investigated with a view to evaluating habitat influences on the fatty acid profile. Fish from the freshwater creek were unpigmented, fresh-run juveniles (referred to as whitebait), the others adult fish. The fatty acids that predominated in adult G. maculatus muscle were 16:0 and 22:6(n-3), and 16:0 and 18:1(n-9), respectively. In whitebait 22:6(n-3), 20:5(n-3) and 16:0 were predominant. Hopkins estuary fish had the highest amount of 18:2(n-6) but the lowest 18:3(n-3). In all galaxiid populations, polyunsaturated fatty acids (PUFA) were the main group of fatty acids in total lipid in muscle, and accounted for more than 40 %, followed by saturates and monoenes. In landlocked populations, the amount of monoenes was lower than in other galaxiid populations. G. maculatus whitebait had significantly lower amount of saturates and the highest amount of n-3 fatty acids. The ratio of n-3 to n-6 PUFA ranged from 4.6 (Hopkins estuary) to 7.6 (whitebait), and the former differed significantly from all the other populations. The main fatty acids predominating in the liver of galaxiids from landlocked (Lake Bullen Merri) and estuarine populations were 16:0, 22:6(n-3) and 18:1(n-9), and generally reflected the corresponding pattern in muscle. A principal component analysis of the fatty acid composition of muscle samples confirmed and highlighted the distinct fatty acid profile of the populations investigated, when three groupings could be discerned. The study suggests that in addition to the diet, other habitat related factors may influence the fatty acid profile in catadromous G. maculatus.

Patterns in fish taxa composition were examined in Portuguese reservoirs to assess whether distinct types of assemblages exist. Furthermore, the environmental variables most tightly associated with assemblage-level patterns were identified. Classification of the fish taxa-by-reservoirs matrix revealed four major groups. Groups were separated by means of canonical correspondence analysis according to (by decreasing correlation with canonical axis): air temperature, annual rainfall, surface elevation, trophic state, mean depth and reservoir placement within the basin. In addition to these variables, stocking practices and predation likely contributed to assemblage composition. Assemblages in group A were distinguished by the permanent presence of largemouth bass (Micropterus salmoides) and the absence of trout (Salmo trutta and/or Oncorhynchus mykiss), nase (Chondrostoma sp.) and barbel (Barbus sp.). Group B assemblages invariably included bass, barbel and nase, while pumpkinseed (Lepomis gibbosus) was frequent and trout was extremely rare. Assemblages in group C were also characterised by nase and barbel, but in contrast to group B, trout was frequent, whereas bass was rare and pumpkinseed was absent. Group D assemblages consisted exclusively of trout and chub (Leuciscus sp.). The relationships observed parallel patterns detected in natural lakes to a certain extent, despite the critical human influence and the probable instability of some of the patterns detected.

The general principles behind the bioenergetic approach for predicting growth, as well as for decreasing feed and nutrient losses, have been set forth for salmonids. Given the diversification of fish farming activities around the world and the ever increasing concern for water quality management, it becomes essential to verify whether an approach developed for salmonids is applicable to other species. Given this general background, an attempt is made here to check the theoretical assumptions and technical considerations behind the bioenergetic principles developed for rainbow trout with other freshwater or marine species. From a conceptual point of view, recent literature data do indicate that as far as nitrogen or energy balance is concerned, the general scheme is as valid for marine species as it is for salmonids, even in quantitative terms. Given the methodological tools available today, it should not be difficult to reduce feed and nutrient losses and to estimate the potential environmental loadings using the same principles for non-salmonids.

Two rainbow trout strains differing in their growth performance were used to study possible interactions between genotype, dietary composition and feed level on their feed utilisation efficiency and voluntary feed intake. Two diets (35 and 45 % of crude protein) and two feeding levels (to satiation or at a restricted level of 2 % of body weight), were used. The two diets were distributed, in duplicate, for each strain, during a four month growth trial. At the end of the experiment the digestibility of the two diets was determined in each strain, using chromic oxide, as a marker, and an automatic system for the faecal collection. The body composition of both strains was also analysed. The final weight of fish of the fast growing strain, fed to satiation, was significantly higher than that observed for fish of the slow growing strain. No significant differences were found between the strains's body weights, when a dietary restriction was made. Results observed for the feed-gain ratio were also similar between the two strains. The apparent digestibility coefficient (ADC) of dry matter and energy were significantly different between the two diets but similar for both strains. Concerning protein digestibility no significant differences were observed for diets, although one of the strains appeared to show a higher ADC for protein. Body composition as well as nitrogen and energy retention were similar for both diets and strains.

A sperm cryopreservation protocol adapted from turbot, was tested on sea bass using either 250-μL straws or 1.5-mL cryovials. A dilution to 1/3 in Mounib's extender and a cooling rate of −65 °C·min−1 allowed frozen sperm to recover an initial motility similar to that of fresh sperm at thawing; however, significant differences in motility (P < 0.001, n = 10 fish semen) were observed at further post-activation times, the motility decrease being faster in thawed sperm. At the experimental scale, triplicate inseminations of 2-mL aliquots (approximately 2 000 eggs) showed a significant fertility decay of thawed sperm compared to that of fresh sperm (P < 0.01, n = 12 fish semen) when a discriminating 35·103 spermatozoa to egg ratio was applied. When 70·103 and 200·103 spermatozoa per egg were provided in the same experimental conditions, no significant difference appeared between the fertilisation rates of fresh and thawed sperm. In order to validate the procedure for production or cryobank purpose, a scaled-up protocol was established. Two and 50 mL batches of eggs (approximately 2·103 and 50·103 eggs, respectively) were inseminated in triplicate using either fresh or thawed individual sperms of 5 males with 200·103 spermatozoa per egg. The mean fertility decreased by 23.5 % due to cryopreservation. This decline was explained by the loss of fertility of only one sperm, and only in large-volume conditions, probably due to the delay of use after thawing.