Brown trout and rainbow trout (average weight 100 g) were reared in fresh water at 12 °C under the same conditions before transfer of brown trout to sea water, in order to compare nitrogen utilisation in the two species. Apparent protein digestibility (ADC), nitrogen (ammonia and urea) excretion, protein productive value (PPV) and actual observed nitrogen mass balance were determined. Rainbow trout raised in fresh water had a higher growth rate (1.1 vs 0.8%.d−1), better food conversion ratio (0.7 vs 1.0), better ADC (91 vs 85%) and PPV (45 vs 35%) and lower ammonia excretion rates than brown trout reared in fresh water. Transferring brown trout to sea water induced lower PPV (30%) and ammonia and urea excretion. Salinity did not modify metabolic efficiency in brown trout. Fat content was higher in brown trout (7.7-8.9% ww) than in rainbow trout (5.7-7.6% ww). Nitrogen mass balance indicated that compounds other than ammonia and urea were produced in higher quantities by seawater brown trout. Behaviour, less domestication and specific ability to utilise protein could explain the differences between the two species.

A study of microhabitat use by fourteen abundant fish species was undertaken in the lower Ntem River Basin in Cameroon (Africa). Seventy-one microhabitats including pools, raceways and riffles were studied twice during the 1994 and 1995 dry season. Results obtained by Canonical Correspondence Analysis (CCA) showed a good niche separation along the ordination axes I (λ1 = 0.37) and II (λ2 = 0.20). Microhabitat selection by these species reflects response to several physical factors including width, depth, current velocity and substrate type. However, a substantial part of the variation in species segregation was explained by both instream (% leaves, woods and roots, and aquatic plants) and bankside (% mean canopy closure)cover. A striking pattern encountered during this study was the frequent size-related variation in habitat use displayed by many species. For example, smaller individuals of Brycinus longipinnis, Barbus camptacanthus, Distichodus notospilus, and D. hypostomatus, occurred more often in faster flowing waters than did their larger conspecifics. The association displayed by CCA was high (0.957 and 0.938, respectively for the first and second axis), and Monte Carlo test (99 permutations) revealed that these associations were significantly different from random (p = 0.01). The implications of these results for habitat management are discussed.

Un modèle écophysiologique déterministe de la croissance, de la reproduction et des interactions entre le bivalve et son environnement estuarien a été élaboré pour l'huître japonaise Crassostrea gigas. Pour fonctionner, le modèle a besoin de la température de l'eau, des concentrations en matière en suspension, matière organique particulaire, matière minérale particulaire, chlorophylle-a, phéopigments, protéines, lipides et glucides particulaires. Les fonctions de filtration, consommation, ingestion, absorption et respiration ainsi que les efficacités de rétention, sélection et absorption sont modélisées à l'aide de variables endogènes (poids sec de l'animal, allocation d'énergie entre la croissance et la reproduction) et exogènes (température, quantité et qualité de la nourriture). Le modèle simule l'évolution temporelle de deux compartiments : somatique et réserves-gonades. L'énergie provenant de la nourriture absorbée est allouée au compartiment somatique jusqu'à un maximum de croissance somatique. Ce maximum décroît avec l'âge du bivalve et ne dépasse jamais 0,02 g.j−1.individu−1. L'énergie en excès est alors attribuée au compartiment réserves-gonades. Cette représentation permet d'identifier les périodes de stockage de réserves et de gamétogénèse ainsi qu'une bonne simulation de l'intensité des pontes.Le modèle tient compte d'une efficacité de sélection plus importante pour les microphytes que pour les particules détritiques. L'efficacité d'absorption a été représentée en fonction du pourcentage de matière organique dans la fraction ingérée afin de tenir compte de la dilution de la nourriture par les particules minérales. L'efficacité d'absorption des microalgues varie de 20 à 60 %, tandis que pour les particules organiques détritiques, le modèle simule des valeurs négatives pour tenir compte des pertes fécales métaboliques. Ces formulations permettent de suivre l'évolution temporelle des quantités de microphytes et de matières détritiques rejetées sous la forme de pseudofèces et de fèces.

The effect of fish farming on dissolved amino acid concentrations, bacterioplankton abundance and exoproteolytic activity was assessed in 3 experimental marine ponds. Different standing stocks of fish were introduced (semi-intensive pond: 250 g.m−2, semi-extensive pond: 50 g.m−2, control pond: 0). Sea bass farming increased dissolved combined amino acid (DCAA) concentrations only in the semi-intensive pond. Bacterial standing stock was unaffected by fish food supply. However, bacterial exoproteolytic activity was strongly stimulated by aquaculture intensification; the average maximal rate of dissolved protein hydrolysis (Vm) increased with intensity (control pond: 1 500 nM.h-1; semi-extensive pond: 2 600 nM.h−1; semi-intensive pond: 5 100 nM.h−1). DCAA fluxes through bacterial exoproteolytic activity ranged between 16 (semi-extensive) and 11% (semi-intensive) of the daily nitrogen input by fish food. Bacterial exoproteolytic activity allowed a substantial part of the increased supply of dissolved amino nitrogen to be incorporated into bacterial biomass, then available for transfer to higher trophic levels within the ponds. It also significantly decreased dissolved organic nitrogen export from the ponds to the surrounding environment.

Fluxes of nutrients (NH4+, NO3-, PO43- and Si(OH)4) were studied on an intertidal mudflat in Marennes-Oléron Bay, France, at two different seasons and at different times of the emersion period. Fluxes through the sediment-water interface were both calculated from vertical profiles of nutrient concentration in pore-water (diffusive fluxes, JD) and measured in light and dark benthic mini-chambers (measured fluxes, J0). Results indicate that ammonia was mainly released in summer while nitrate was mainly taken up in late winter. This uptake from the overlying water was probably due to the coupling of nitrification-denitrification within the sediment. The J0/JD ratio further indicates that bioturbation likely enhanced ammonia release in summer. Concerning phosphate, the comparison of diffusive and measured fluxes suggests that PO43- could be assimilated by the biofilm in winter while it was released in summer at a high rate due to both bioturbation and desorption because of the relative anoxic conditions in summer. Silica was always released by the sediment, but at a higher rate in summer. Statistically significant differences in measured fluxes were detected in dark chambers at different times of low tide, thus suggesting a short-term variability of fluxes. Microphytobenthos preferred ammonia to nitrate, but assimilated nitrate when ammonia was not available. It also turned out that benthic cells could be limited in nitrogen during low tide in late winter. In summer, ammonia was not limiting and microphytobenthic activity significantly decreased the measured flux of NH4+ in the middle of low tide when its photosynthetic capacity was highest.

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 study of abundance of small-bodied species of fish such as minnow is important because these species play an important role in the food-web dynamics of small streams. In this work, we propose the use of an Artificial Neural Network (ANN) to the modelling and prediction of abundance in minnow Phoxinus phoxinus using 10 environmental microhabitat variables: distance from the bank, percentage of boulders, pebbles, gravel, sand, mud, marl, cover respectively, depth and velocity. A total of 372 points were randomly chosen from a total of 465 electrofished point samples to establish a ANN model. A validation holdout of the training of the ANN was undertaken with testing on 93 other sampling points. On the test set, the prediction performance was 92%. Our study showed the advantages of the back-propagation procedure of the neural network in the field of stochastic approaches to ecology of coarse fishes. The limitations of the neural network approaches as well as statistical and ecological perspectives are discussed.

Wild Atlantic mackerel, Scomber scombrus, were kept in net cages and fed a high energy salmon diet rich in (n–3) polyunsaturated fatty acids for 8 months. Analyses of whole body and muscle were performed at regular intervals on 1 and 2-year-old fish. The percentage of lipid and dry matter increased in whole body and muscle as the fish weight incrcased from catch to market size over the course of the following year. In all groups of fish examined the sum of fatty acids (n–3) as the percentage of total lipid in muscle decreased from 33 to 26%, while the sum of monoenoic acids increased with 10% from 39 to 49%. Vitamin E concentration of muscle increased substantially during feeding. The oxidation status of the fish muscles was very good at the end of the feeding period, with thiobarbituric acid values of less that 3 µmol kg−1. At theend of the feeding experiment large fish to be sold at market were starved for two weeks. Analyses of the nutritional and oxidative state of muscle showed that transport, slaughter and storage did not affect the lipid content or the fatty acid composition. Low and stable thiobarbituric acid values were observed, while vitamin E content significantly decreased during processing and storage at −30 °C, which indicates that vitamin E was an effective antioxidant in mackerel muscle.

Vitellogenin (VTG) levels were measured in the plasma of 143 female skipjack tuna, Katsuwonus pelamis caught in the Western Indian Ocean. These levels were correlated with the gonadosomatic index (GSI) and with plasma 17β-estradiol (E2) levels during the reproductive cycle. VTG and E2 levels were measured using a competitive enzyme-linked immunosorbent assay (ELISA) and a radioimmunoassay (RIA), rcspectively. VTG was purified from a pool of plasma obtained from females with high GSI using a double chromatography method (gel filtration and ion exchange). A specific antibody was obtained in rabbits. The VTG immunoenzymeassay developed gave an assay detection limit (90% binding) of 15 ng.ml-1. Mean VTG levels ranged from 1.2 mg.ml−1 to 4 mg.ml−1. Mean monthly VTG values remained relatively elevated during the resting periods (1.2 mg.ml−1 in April and 1.9 mg.ml-1 in September), while maximum levels reached only 4 mg.ml−1 during the reproductive season. The highest GSI values were observed from November to March during the major reproductive season corresponding to the North monsoon and from early June to late August during the minor reproductive season corresponding to the East monsoon. Lowest GSI values were found in April-May and September-October. Mean E2 levels exhibited considerable variability among all females sampled ranging from 700 pg.ml−1 to 9 ng.ml−1. This study demonstrated that the sexual maturation was correlated with the monsoon seasons and that there was a positive correlation between monthly variations of GSI, VTG and E2 levels in the skipjack tuna population from the Western Indian Ocean.

Ce travail analyse l'aire de répartition marine actuelle de l'esturgeon européen Acipenser sturio à partir de 179 déclarations de captures accidentelles (dont 125 recaptures) correspondant à la période 1980–1994. Cette espèce menacée se rencontre du sud du golfe de Gascogne jusqu'à la Scandinavie et dans l'ensemble des îles Britanniques. Il est démontré que cette aire de répartition est bien celle de la population se reproduisant dans le bassin versant Gironde-Garonne-Dordogne. Les captures sont faites sur des fonds de moins de 100 m, sur des substrats variés et de façon équivalente par des chaluts de fond, des filets maillants et des filets tramails à l'occasion de la pêche de poissons ou de crustacés benthiques. Les esturgeons capturés sont surtout des immatures mesurant en moyenne 113 cm (min. 35 cm, max. 244 cm). Les captures ont principalement lieu durant les 6 premiers mois de l'année et sont en phase avec celles observées dans l'estuaire interne de la Gironde. Ce type de données, malgré des limites liées à leur naturemême, permet dans le cas d'espèces rares et/ou migratrices d'obtenir des informations intéressantes et inaccessibles par ailleurs sur leur écologie marine.

Long-term effects of constant exogenous ammonia concentrations were investigated in two different batches of turbot juveniles (53 and 73 g) under controlled environmental and feeding conditions. Over the 84-day experiments, ambient un-ionized ammonia (UIA-N, NH3) concentrations were steady (coefficient of variation, 12-16%) and water pH range was 7.88-7.99. Survival was maximum up to 0.33 mg.l−1 UIA-N and at 0.73, 50% mortalities were observed on day 52 (73 g) or day 77 (53 g). No-growth concentration was 0.73 mg.l−1 UIA-N in the two groups and the 84-day lowest-observable-effect oncentration range 0.14-0.33 mg.l−1. In the most tolerant group (53 g), the 84-day no-observable-effect concentration was 0.14 mg.l−1 UIA-N. The estimated 28-day efficient concentration that gave 50% of the specific growth rate of controls ranged from 0.60 to 0.75 mg.l-1 UIA-N. Specific growth rate to ambient ammonia concentration patterns were different in the two groups for the lowest concentrations (0.14-0.34) and similar to food intake to ammonia pattern. Food efficiency was negatively correlated to ambient ammonia concentration, with major changes in food conversion ratio, and protein utilisation observed above 0.33-0.70 mg.l−1 UIA-N. The main change in body composition was an increase in water content in all ammonia-exposed fish. A significant increase in urea-N excretion rate was also observed over 0.33 mg.l−1 UIA-N. Thresholds for growth were affected by exposure duration. Turbot juveniles growth capacity may be depressed by usual ambient ammonia concentrations under intensive farming conditions.

This is an overview of the hormones which may be involved in food intake control in fish, and some hypothetical pathways of their action are given based on mammalian knowledge. Most of the observed effects of these hormones may result from four types of mechanisms, each hormone acting by one or several as follows: (1) hormones could have a direct effect on central nervous system centres, associated with food intake behaviour or via vagal afferent neurons; (2) an indirect effect may occur via the gut which slows gastrointestinal transit, thus resulting in stomach distention which activates vagal afferent neurons; (3) they could have an indirect effect, acting directly on intermediary metabolism via glucose, free fatty acids or amino acids mobilization or storage; (4) the last possible pathway is an indirect effect by modifying directly or indirectly secretions of other hormones involved in food intake control. Some of these hormones (CCK, PYY, glucagon, adrenalin) act as short-term factors which regulate meal ingestion and are generally inhibitory factors. On the other hand, other hormones (GH, TH, and leptin) require more time to modify foodintake behaviour, and appear as stored calorie regulators. However, the orientation of hormones to short-term or to long-term action is not always clear as it has been noted for insulin and glucocorticoids, and may depend on the hormonal and metabolite environment.

La dynamique de production du rotifère Brachionus calyciflorus en conditions contrôlées et sa qualité nutritive en tant que source alimentaire pour les larves de poissons d'eau douce sont évaluées après une détermination du taux de développement de cet organisme sur l'algue Dictyosphaerium chlorelloides. Ces aspects sont examinés par le biais d'une série d'études portant sur la dynamique de population (taux de production journalier, durée de développement embryonnaire et temps de génération minimum, fécondité des femelles amictiques) et sur la composition biochimique de ces organismes. La durée de développement embryonnaire, fortement dépendante de la température, varie entre 7 et 13,4 h. Les rotifères atteignent leur meilleur taux de reproduction à 25 °C, soit en moyenne 22,1 œufs par femelle. L'origine des femelles utilisées (jeunes femelles amictiques ou femelles précultivées sur D. chlorelloides) influence les résultats de production en masse, avec des densités atteignant, en fin de production, respectivement 245 et 188 rotifères par ml. En ce qui concerne la qualité nutritionnelle des rotifères, la teneur en protéines brutes varie peu au cours du cycle de production (53,5–54,1 % de la matière sèche). Parmi les acides gras, l'acide linoléiqueC18:2n-6 est le plus abondant dans les rotifères, et représente, en fin de cycle de production, 42 % des acides gras identifiés chez les femelles précultivées sur D. chlorelloides.

The proportion of vibrio E, dominant in healthy turbot larvae, was artificially increased in the rotifer enrichment medium. The main effect of this vibrio enrichment was to improve the resistance of larval turbot challenged with a pathogenic strain of Vibrio splendidus, vibrio P. The improvement of the survival rates was significant with 1.5 × 106 CFU of vibrio E added per ml of enrichment medium, and it was still maximum at the highest dose tested (5 × 107 CFU.ml−1; 80 ± 2% of survivors after 48 h of challenge, versus 50 ± 2% for the control group).

Further in vitro characterisation showed that vibrio E was able to grow in the presence of the chelating agents EDDHA and EDTA, while producing siderophore, as revealed by chrome azurol S dyeing. The pathogenic vibrio P did not grow on iron-depleted medium, and it did not seem to produce siderophore. Consequently, a second experiment attempted to appraise the role of iron availability in the interaction between the pathogenic and probiotic vibrios. To this end, turbot larvae were fed with rotifers treated by the bacterial siderophore deferoxamine. This treatment significantly increased the resistance of larvae chal-lenged with vibrio P in comparison with the control group, but to a lesser extent than the group enriched with vibrio E. There was also an increase of the growth rate due to either the siderophore treatment or thevibrio enrichment, as well. No further improvement was observed when the rotifers were simultaneously both treated and enriched. It was concluded that the probiotic effect of vibrio E may be at least partly due to competition for iron with the pathogen.

A physiological model has been developed to provide a simulation of scope for growth responses of cockles Cerastoderma edule to environmental factors such as temperature and seston parameters. As in previous treatments, model structure consisted of a series of equations representing the vanous physiological processes which are integrated in the energy balance of filter-feeders. Unlike these treatments, however, the present model was designed to give account of the separate processing of phytoplankton and detritus, as components of suspended food that are submitted to differential selection and absorption. In this way, effect of quality indexes based on phytoplankton abundance on growth rates could be explored. Subsequently, we have applied this model to: (a) simulating scope for growth under conditions subjected to variation in the estuarine media, and (b) predicting growth variability as a function of food regime, by comparing two particular estuaries with contrasting seston characteristics.

L'étude de la maturation et de la ponte de l'huître creuse Crassostrea gigas, s'intègre dans une large problématique visant à comprendre les causes de mortalité qui surviennent épisodiquement dans le bassin de Marennes-Oléron au printemps et en été. Un conditionnement thermique et alimentaire des élevages permet d'obtenir simultanément des huîtres à tous les stades de maturité sexuelle. Le calcul des taux de filtration, consommation, absorption et respiration permet d'estimer le potentiel de croissance, et donne le bilan énergétique des huîtres aux différents stades sexuels. Les réponses physiologiques sont semblables pour des huîtres mâles ou femelles. La filtration de 2,4 à 2,6 1.h−1, passe à 1,8 1.h−1 à un stade de maturation avancée. La prise de poids liée au développement des gonades ne semble pas avoir d'effet sur le taux de filtration. Les huîtres de 2,5 ans présentent un bilan énergétique déficitaire (–15 J.h−1) à un stade de maturation avancée. Ce déficit est confirmé (–90 J.h−1) sur des huîtres de 1,5 ans au même stade de maturation. En revanche, les huîtres immatures, en début de maturation ou en post-ponte, ont un potentiel de croissance compris entre 110 et 170 J.h−1 . Le déficit énergétique observé au stade de maturation avancée relève essentiellement de la fonction d'absorption qui chute de façon importante en période de forte gamétogenèse. L'étude de la respiration permet de définir une allométrie particulière à la croissance gonadique avec un coefficient d'allométrie de 0,574. La faiblesse physiologique des huîtres, observée à un stade de maturation avancée, doit être prise en compte dans la recherche des facteurs responsables des mortalités printanières et estivales affectant les cheptels en élevage dans le bassin de Marennes-Oléron.

The capability of turbots to use self-feeders was studied using 3 groups of 100 juveniles. Feeding activity reached a plateau after 20 days. Almost all feeding activity was observed during the photophase, and the acrophase was associated with dawn. The proportion of nocturnal demands was the highest in the replicate with the lowest feed efficiency, suggesting that feed waste was mainly occurring during nocturnal feeding activity. During the last 30 days of the experiment, demands were only rewarded during two periods of 2.5 h.day−1. Feed efficiency was improved and was homogeneous between the three tanks, but the voluntary feed intake was reduced. It is concluded that turbots are able to use self-feeders but they do not adapt quickly, and they are not able to compensate a reduction of feed access by increasing demand activity during the access period.

In mollusc hatcheries and nurseries, live microalgae are traditionally used as feed for bivalves. Despite recent improvements in efficiency, such intensive culture of microalgae represents major cost factors in the production of bivalve larvae and spat. In an attempt to provide cost-effective alternatives and to simplify hatchery-nursery procedures, non-living algal food has been developed over the past few years. Substitution products such as bacteria, yeast, vitamin or docosahexaenoic acid enriched powders, dry and concentrated microalgae and microcapsules have been tested and evaluated on an experimental scale. The present article reviews major research aimed at developing non living diets in mariculture, which generally resulted in lower growth and higher mortalities than that recorded for controls fed live microalgae. At the present time, concentrated and dried microalgae appear to be the best alternative products for bivalves, for juveniles essentially, while microcapsules provide an excellent research tool to study their nutritional requirements.

If recovery programmes are to be initiated in England and Wales, it is very important to obtain information on how genetic variation is partitioned between the remaining populations for the endangered species Austropotamobius pallipes pallipes. A survey of the mtDNA genome, using 12 restriction enzymes revealed 3 haplotypes in 4 British populations. The study reveals a low level of genetic variation amongst four geographically distant populations. Moreover, the most widespread haplotype found in the British populations is also similar to those found in French populations; one of the rare haplotypes found in one English population is also widespread in French populations. Management of crayfish stocks may be possible at a national level however, a more extended study of mtDNA variation is needed to prove this conclusively.