Measurement of total body electrical conductivity (TOBEC) recently has been used to estimate the body composition of several fish species in a noninvasive manner. The present study was conducted to evaluate the use of TOBEC in estimating body composition of largemouth bass (Micropterus salmoides). A total of 85 largemouth bass weighing 154 to 3245 g were measured for electrical conductivity after which their proximate composition was determined by chemical means. Significant linear relationships existed between the natural logarithm of whole-body ash, lean body mass, lipid, protein, and water content and the natural logarithm of length and/or weight with r2 values ranging from 0.860 to 0.999. Inclusion of the TOBEC value did not significantly improve the prediction accuracy of these models. Equations were developed to allow the prediction of body composition of largemouth bass based on length and weight measurements. Prediction models including only length and weight as variables provided estimates of body components of an independent set of fish that were not significantly different from chemically derived measurements of these components. These models should allow the rapid, nondestructive estimation of body composition of largemouth bass varying in size and condition without the added cost and processing time associated with measurement of TOBEC, although large prediction errors might prevent the detection of ecologically significant differences in body composition. However, with additional data involving narrower fish-size ranges and constant temperatures for the development of prediction equations, TOBEC may improve the prediction accuracy of body composition estimates for largemouth bass.

Analyse des écailles de truites acclimatées aux îles Kerguelen, archipel du domaine subantarctique, a permis de démontrer la périodicité annuelle des anneaux par différentes méthodes donnant des résultats convergents (analyse des fréquences de longueur, marquage-recapture, chronologie de l'apparition des anneaux sur la marge des écailles). Après un long arrêt de croissance hivernal, l'anneau apparaît sur la marge de l'écaille en octobre-novembre, lors de la reprise de croissance. Les critères objectifs d'identification de l'anneau sont identiques pour les truites de mer et pour les truites non migratrices; ils mettent en évidence un arrêt complet de croissance plutôt qu'un changement de rythme correspondant à un ralentissement de cette dernière. Les basses températures hivernales (5 mois à moins de 3 °C) alliées à une faible disponibilité de faune endogène expliquent l'arrêt de croissance. Malgré les faibles variations saisonnières des facteurs environnementaux (températures moyennes estivales ne dépassant pas 10 °C en eau douce et 7 °C en mer), on constate une grande variabilité de la croissance scalaire entre individus. En conclusion, les écailles peuvent être utilisées pour les étudesdémographiques, sous réserve de validation des déterminations à tous les âges.

Virtual population analysis (VPA) is often used for assessing freshwater and marine fisheries resources. One important component in VPA is to calibrate abundance estimates with a time series of abundance indices. One of the commonly used calibration processes usually includes simultaneous estimation of cohort sizes across all ages and years. This reduces the flexibility of the model in accounting for age- and year-effects, in particular in the presence of an age-specific curvilinear relationship between abundance index and stock abundance. In this study, we compared this simultaneous method tuning approach with a stepwise approach which calibrates abundance age by age in tuning VPA. The simulation study suggests that the stepwise procedure tends to perform better with no obvious retrospective errors in the estimated stock biomass compared with the simultaneous method which tends to have large positive retrospective errors. In applying the stepwise procedure and simultaneous method to a cod fishery data set, we found large differences in the stock sizes estimated for the most recent year using these two methods, with the current stock size estimated using the stepwise method being substantially smaller than that estimated with the simultaneous method. Considering the likelihood of the presence of curvilinear relationship between abundance index and stock abundance, we conclude that the stepwise method yields more reliable results, and is less risk-prone in using VPA for fisheries stock assessment.

Males of Myleus ternetzi, at various maturation stages were netted in a French Guyana river. Testes were histologically and ultrastructurally analysed. Leydig cells were always present in large numbers. In mature or almost mature testes, they were characterized by a large spherical nucleus and an extensively developed smooth endoplasmic reticulum (SER) composed of very narrow tightly packed tubules. In regressed testes, most of the Leydig cells had a smaller nucleus with an irregular shape, a disorganized SER and the fine structure of the mitochondria was greatly affected. These changes would reflect different phases throughout a metabolic cycle in relation to spermatogenesis.

The use of an image analysis microsystem with a specially developed software enabled scale image processing, outline extraction and computation of features which are not available in the conventional approach of scale analysis. Those parameters (shape factors, moment invariants and elliptic Fourier coefficients) were introduced into a discriminant analysis process to test their usefulness in stock identification. The method was applied to European stocks originating from Norway (Etne river) and France (Elorn river). The low misclassification rate obtained indicates that this approach is particularly promising.

Fish Farming enriches the water column in dissolved organic and inorganic material. These materials excreed by the fish, elutriate from uneaten food and derive from other polluting substances. Ratios of the organic/inorganic forms of substances (for example N and P) are thus modified. Such perturbations in turn affect phytoplankton development. From in vitro analyses and tests of water taken from a turbot rearing tank, we show the changes in seawater chemical composition produced as well as the way growth was modified in three phytoplankton species: the diatom, Chaetoceros gracile, and the dinoflagellates, Gymnodinium cf. nagasakiense and Alexandrium minutum. Elutriates from the granules used for feed (0.1 to 100 mg.l−1) were found to be stimulating, particularly for Gymnodinium. Alexandrium was strongly inhibited both by turbot-tank water diluted 10-fold with coastal seawater and by diluted faeces elutriates. Urea added at low concentrations (1 to 2.5 µmol.l−1) inhibited growth in Alexandrium and Chaetoceros, but at 1 µmol.l−1 it stimulated growth in Gymnodinium. The antibiotic, Oxytetracycline was complex in its effects, with growth inhibition being observed in Chaetoceros and Gymnodinium, but stimulation in Alexandrium (at 0.2 mg.l−1). In general, we found fish farming to allow phytoplankton growth, except for Alexandrium in a few cases. Additions to the water from fish farming may regulate growth in some species. As such additions act differently on growth in different species, fish farming is likely to markedly modify species composition in its vicinity.

The fatty acid profile of four different genetic strains of Clarias gariepinus: gold (G), Netherlands (N), RAU (K) and Wild (W) were evaluated. Fertilised eggs and larvae of the four strains were maintained under identical environmental conditions. After nine weeks, the two faster growing strains (G and W) had less total body lipid than the others (N and R). The total saturated (SFA), monounsaturated (MUFA) and polyunsaturated (PUFA) fatty acids of the four strains were: G – 32.1; 26.8 and 37.9%; N – 33.5; 27.8 and 35.5%; R – 32.7; 29.0 and 35.4%; W – 32.9; 27.7 and 36.8%, respectively. The major fatty acids that showed statistically significant differences between strains were: C16:0, C18:1ω9, C22:5ω3 and C22:6ω3. The G strain had a significantly higher ω3/ω6 ratio (2.2) compared to that of the other strains (N – 1.9; K – 1.9 and W – 1.9). In a second trial, juveniles of strain G were fed an artificial diet for 60 days containing no lipid (A, control), or the following lipids at 10% of the diet, sunflower oil (B. a high level of C18:lω9 and C18:2ω6), cod liver oil (C, a high level of 20 and 22 Cω3 fatty acids) and tallow (D, predominantly SFA and MUFA). Muscle total lipid composition was strongly influenced by diet and contained the following SFA, MUFA and PUFA percentages, and a ω3/ω6 ratio of: A – 35.9; 45.3; 15.0% and 0.5; B – 30.6; 33.4; 33.6% and 0.1; C – 33.2; 37.2; 23.6% and 1.8; D – 38.7; 45.3; 12.1% and 0.4, respectively.

Le présent travail est consacré à l'étude de la maturation sexuelle d'une cohorte née en 1977 d'Eledone cirrosa dans le golfe du Lion en Méditerranée. Plusieurs indices de maturation tel que le rapport gonado-somatique, l'indice de Guerra pour les deux sexes, l'indice du pénis pour les mâles ainsi que l'indice de la glande de l'oviducte sont examinés en vue de choisir le meilleur moyen d'exprimer numériquement les différents stades de maturation de l'espèce pour des études de populations. Dans ce but, l'on suggère d'utiliser l'indice de Guerra pour les mâles et l'indice de la glande de l'oviducte pour les femelles pour lesquels trois phases de maturation (immature, intermédiaire et mature) peuvent être différenciées. Les clefs numériques correspondant à trois phases de maturation avec les indications des observations du développement de la gonade sont établies.

Reliable data on tilapia nutrition and feeding are scarce. In the best documented field, that of protein requirement, current data show good agreement with available information on coldwater and warmwater fishes. Various feedstuffs have been used to satisfy the protein needs, but the effects of variations of their quality have not been sufficiently studied. The main problem lies in the assessment of the effects of natural food in open rearing structures; thus there are some discrepancies with the results obtained in laboratory. More insight on in situ nutrition of pond fish, as well as the management of the feedstuffs and feeding practices is needed.

Two specific Enzyme Linked lmmunosorbent Assays (ELISA) for vitellogenin were developed using two different antisera anti-plasma vitellogenin purified by SDS polyacrilamide gel electrophoresis and electroelution. Purified vitellogenins migrated as single bands under SDS conditions with an apparent molecular mass of 154 and 152 kDa for Chrysichthys nigrodigitatus and Heterobranchus longifilis respectively.The ELISA was performed on 96 well microtiter plates using specific antibodies raised on rabbits and a second antibody (Goat anti-rabbit) labeled with peroxidase. Parallel displacement curves were obtained between purified vitellogenin and female plasma as well as plasma from estradiol treated fish. Both antibodies cross-reacted with the heterologous vitellogenin but the curves were not parallel, indicating different antigenic structures of the two vitellogenin molecules from the two catfish species. The reliability and the specificity of these assays allowed us to quantify vitellogenin in plasma samples during vitellogenesis of the two species. The annual vitellogenin plasma levels presented a good correlation with mean oocyte diameter and reproduction period in Chrysichthys nigrodigitatus. In Heterobranchus longifilis the mean oocyte diameter is almost constant all year round, but vitellogenin levels presented significant variations with higherlevels corresponding mainly to the low gonado-somatic index values observed during the dry seasons.

The occurrence of new phytoplankton species in a coastal area may be explained by the import of shellfish containing whole live algal cells in their digestive tracts. Indeed, shellfish containing toxic algal cells can induce both primary contaminations in safe areas (initially free from toxic microalgae), and secondary contaminations of other shellfish growing in the same area via the faeces of the imported animals. To mitigate this problem, shellfish need to be placed in a separate holding tank and their intestinal content purged. For a deeper understanding of the risks associated with transferring contaminated shellfish, oysters (Crassostrea gigas) and mussels (Mytilus edulis) were purposely fed either Alexandrium minutum or A. catenella (Dinophyceae) or Pseudo-nitzschia calliantha (Bacillariophyceae) toxic algae for 2 h. They were then transferred into individual tanks where they were continuously fed with a non-toxic alga, Tetraselmis suecica. Biodeposit production, faeces composition, and filtration rates were monitored for the shellfish over a 6-h period. The effect of temperature differences and different initial toxic algae concentrations were compared. This study revealed a relationship between temperature and cell lysis in the oyster digestive tract. It also indicated that toxic algae concentration did not seem to influence gut passage time in oysters, while a significant effect was observed in mussels, and confirmed the existence of a difference between oyster and mussel feeding patterns.

The application of a simple, fast and reliable volumetric microrespirometric method to assess respiration of bivalve larvae is discussed. As a model, C. gigas larvae of various sizes were used. Metabolic activity of veliger larvae was assessed by measuring respiratory rate for use in ecophysiological modelling. As an example of the application of this approach, additional measurements of veliger respiratory rates were carried out to assess the effect on larval metabolism of different concentrations of leachate from wood treated with chromated copper-arsenate (CCA).Veligers of Crassostrea gigas (length from 95 to 331 µm) were fed with a mixture of Isochrysis galbana and Chaetoceros pumilum cells. Experiments were performed in a 20 °C constant seawater temperature. The wet and dry weight of four length (L, in µm) classes of larvae were obtained from which the relationship between total dry weight and veliger length was derived {DW = e (3.27+L×0.0154)} (R 2 = 99%). Moreover, tissue dry weight (TDW; in ng) was calculated according to Gerdes (1983). Since the mathematical model between larval length and respiratory rate explained 88% of the total variability, a more conservative approach using oyster larval dry meat weight (in ng) and respiratory rate (in µl O2 h−1) was developed to establish a linear model explaining 94.5% of the variability: Resp. = -3.849 × 10-4 + 5.211 × 10-6 × TDW. These experiments provided updated figures of C. gigas larval respiratory rates for use in ecophysiological models. The relationship between tissue dry weight and respiratory rate was close to previous estimates obtained by Gerdes (1983) and Hoegh-Guldberg and Manahan (1995) at 25 °C and 20 °C respectively. Our experiments demonstrate that volumetric microrespirometry is suitable for assessing larval respiratory rate and therefore can be used to assess impacts of pollutants on an early larval stage. Oysters exposed to leachates from chromated copper arsenate (CCA) treated timber at 5 kg m−3 showed initially highly variable respiratory rates while those rates decreased drastically for a 15 kg m−3 CCA treatment exposure. Among bioindicators using physiological response to assess pollutant effects, swimming activity and respiratory rates can be compared, the later showing a significant response at a lower pollutant concentration.

L'association d'un prédateur à l'élevage de tilapias pour en contrôler la reproduction indésirable est aujourd'hui effectuée par un nombre croissant de pisciculteurs africains. Dans ce cadre, les Siluriformes (Clarias ou Heterobranchus sp.) sont souvent considérés comme ayant une double fonction : prédation et polyculture. Les résultats d'élevage associés Clarias gariepinus-Oreochromis niloticus montrent qu'un nombre important d'individus de Clarias gariepinus est nécessaire au contrôle total de la reproduction des juvéniles d'O. niloticus mis en charge et qu'ils exercent une compétition vis-à-vis des ressources alimentaires disponibles (aliment et/ou engrais) dans l'étang. Pour contrôler une population de 1 200 tilapias (mâles et femelles) en étang de 10 ares, une population de 260 Clarias gariepinus de poids moyen initial supérieur à 150 g est nécessaire et la croissance des tilapias est inférieure à celle d'un élevage identique dans lequel C. gariepinus est remplacé par un prédateur strict (Hemichromis fusciatus). Ces résultats, confirmés avec un autre Siluriforme, Heterobranchus isopterus, conduisent à privilégier dans le Centre Ouest de la Côte d'Ivoire la pratique d'une polyculture basée sur 3 espèces: O. niloticus, un prédateur strict (Hemichromis fasciatus ou Parachanna obscura) et un siluriforme, Heterohranchus isopterus dont la vocation n'est pas de contrôler la reproduction des tilapias mais de contribuer quantitativement et qualitativement à la production finale. H. longifilis, quant à lui, présente un taux de croissance trop élevé pour ce type d'association, entraînant rapidement un écart de taille avec les tilapias mis en charge sur lesquels il exerce une prédation de même que sur les carnassiers stricts sans contrôler efficacement la prolifération d'alevins de tilapias. Les rendements en H. isoprerus (0,l individu.m−2) peuvent atteindre 1 t.ha−1.an−1 et un poids moyen de 500 g après un cycle de 6 mois d'élevage. Sur la base de ces résultats, obtenus en vraie grandeur, cette logique de polyculture s'est déjà imposée auprès de nombreux pisciculteurs ivoiriens et semble pouvoir constituer un système d'élevage à vulgariser pour l'avenir.

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.

Gaps in our knowledge of basic fish ecology have provided impetus for development of novel “ecology tags” to detect and quantify hard to observe behaviors such as spawning, schooling and feeding. The acoustic environment is one source of potentially useful information about these behaviors. We implanted an acoustic recording tag (Bioacoustic Probe) into the gut cavity of a blacktip reef shark to determine whether an implanted tag could successfully record external and internal sounds. The tag successfully recorded reef fish vocalizations, boat engine noise, the sound of the shark feeding and unidentified rhythmic sounds that may derive from shark tail beats. Technical challenges remain, but sound recording tags have the potential to provide novel insights into shark and fish ecology.

This study performed in the Patapédia River (Québec, Gaspésie) was designed to examine the space utilization and mobility patterns of individual Atlantic salmon parr over short time scales with frequent detections of position. In August 2004, n = 7 radio-tagged Atlantic salmon parr were located every 20 min during 10 tracking periods chosen to take into account the dawn, day, dusk and night periods. Parr showed important inter individual variability in space utilization and mobility patterns, occupying large home ranges (123 to 5602 m2) and sometimes migrating 2 km upstream in the river. No differences were observed in the mean distance travelled among the four daily periods by individual fish, but the estimated home ranges utilized during the four daily periods overlapped only partially, demonstrating that parr partly occupy different areas of the river during different parts of the daily cycle. The results suggest that an intense survey on a small number of fish may contribute to a complementary comprehension of space utilization and mobility patterns of Atlantic salmon parr when viewed in association with results from studies surveying larger number of fish at lower frequency.

La tolérance aux basses températures des gamétophytes de l'algue alimentaire Undaria pinnatifida est examinée selon différentes méthodes de cryoconservation. La conservation à -80 °C dans une solution glycérolée à 28 % et celle à −196 °C dans une solution en eau de mer de glycérol à 5 ou 10 % ne permettent que des survies de, respectivement, 9 et 4 jours. Par ailleurs, la viabilité n'est pas affectée par un refroidissement de 5 °C/min et une conservation de 15 minutes à −15 °C sans milieu de cryoprotection mais est fortement diminuée par un stockage de 15 minutes à −30 ou −196 °C, même en présence de DMSO. La réduction de la survie des gamétophytes se traduit morphologiquement par une dépigmentation et/ou une contraction des cellules.