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Water quality assessment is a key factor in the environmental management of freshwater networks, especially those including fish farms, which need cost-effective operational tools to monitor and control their waste output. In France, current legislation specifies limits in concentrations of dissolved compounds and suspended solids at fish-farm outlets. Despite the development of mass-balance modelling tools, chemical analysis of water (hydrological method) remains the most widely used method. To understand better the environmental impact of trout farms on aquatic ecosystems and to compare waste assessment methods, we monitored 20 commercial flow-through trout farms for 24 h, and we compared data obtained with the two methods (hydrological method and mass balance modelling) by linear regression. For total nitrogen and total phosphorus, the correlation between the two methods was high; thus, considering the uncertainty of both methods, this study was not able to determine which was more accurate. The high correlation between observed ammonia concentrations and predicted total nitrogen emissions provides a coefficient for estimating ammonia emissions at the farm level. The same approach is proposed for the evaluation of phosphate emissions. In conclusion, this study confirms the utility of simulation modelling for assessing nutrient release from fish farms.

International audience; Fractional factorial design is a practical approach for studying multiple factors, with a minimum of experimental units. The objective of this work was to study the simultaneous effects of nutritional and environmental factors on both growth and flesh quality of common perch (Perca fluviatilis), a new inland aquaculture species. This study sought answering the two following questions: (i) which combinations of factors allow improving growth, food efficiency, and technological, sensorial and nutritional qualities? (ii) is it possible to simultaneously improve growth performances and flesh quality? In a first experiment, twelve factors (7 nutritional and 5 environmental factors) were each tested at 2 levels in a fractional factorial design in 24 independent recirculating 500 L tanks. The best 4 combinations identified in this first experiment were then validated in a second experiment. The first phase of the multifactorial approach used here allowed revealing emergent information: i) there is a combination of factors that allows reducing both the heterogeneity of the production and the losses of nitrates and phosphates, while preserving good characteristics of growth and quality of fillets; ii) it is possible to improve the quality of the aquatic production system, without decreasing significantly growth efficiency; iii) the effect of a given factor, even such an important one like diet, temperature or target biomass, depends on the levels of the other rearing factor levels, thus the usual reference optimum used for a given factor has no meaning theoretically and can be questioned according to the levels of the other factors which act altogether on the functioning of the rearing system. The input factor combinations resulting in a significant enhancement of single output variables or several output variables were identified (e.g. improvement of feed efficiency, and/or fillet docosahexanoic acid content). Our results clearly demonstrate a strong interdependence of input factors into the animal rearing system, particularly between nutritional and environmental ones.

Fish schools are aggregative structures encountered in all types of aquatic environments but have as yet been little studied in freshwaters except at small spatial scales. This study represents the three dimensional description of juvenile fish schools (Perca fluviatilis and Rutilus rutilus) in a lake environment using high resolution multibeam sonar system operating at a frequency of 455 kHz, composed of 60 beams of 1.5 degrees allowing a 90 degrees observation plane. The in situ diurnal schooling behaviour of young-of-the-year fish of both species is confirmed. The morphological, energetic and spatial variables of these schools are described and related to one another. The structures described are of the same order of magnitude as those described in the marine environment. The school shape is elliptical, they are shallow and they display a temporal and spatial stability over the Course of a day but a highly variable morphology. The number of vacuoles, a descriptor of the internal morphology of the schools, was found to be significantly (p < 0.01) correlated with the volume of the school, and showed two distinct relationships, with proportions similar to the percentage occurrence of both species sampled by a pelagic trawl. The relation may be efficient for fish species discrimination by 3-D acoustics methods in this lake with two main aggregative fish species.

International audience; The development of acoustics tools and methods for monitoring anthropized ecosystems represents a new field for the application of acoustics. Monitoring such an environment was not possible with single vertical echo sounders, due to the fact that the artificial structures and the natural targets were not distinguishable. Monitoring data were collected along the French Mediterranean coastline, during five short surveys of mussel culture longline areas. Both the Reson Seabat 6012 multibeam sonar (455 kHz) and the Simrad SR 240 omnidirectional sonar (23.75 kHz) were used for target detection. The former tools allow accurate allocation of the different types of echoes to artefacts, fish schools and scattered fish. The school characteristics collected included morphological, geographical (GPS, school location), and behavioural (connections with the longlines). An acoustic survey undertaken with the same hardware near the study area allowed the comparison of fish schools and the TS distribution of individual fish in the open sea and in the mussel area. These data permitted us to evaluate the ecological impact of a mussel culture on the ecosystem, in a context of predation behaviour of fish on these longlines. Finally, the acoustic data revealed the configuration of each concession and the level of charge of each line. We discuss the applicability of this technology for in situ real time monitoring for joint management of such ecosystems. The information can allow littoral cooperative management or incorporating it into an ecosystem approach.

Apparent digestibility coefficients (ADCs) of macro- and micronutrients and energy of two diets were measured with common carp Cyprinus carpio reared at two water temperatures (18 and 25 °C). Two diets containing either soy protein concentrate (SPC) or Norwegian herring meal (FM) as a major protein source were formulated. Dicalcium phosphate was incorporated at a level of 4 % of the former diet. Duplicate groups of 20 fish (body weight: 55 g) were fed by hand twice a day to apparent satiety. After a 7-day conditioning period, faecal collection was made over 10 days using an automatic faeces collector. ADC of dry matter was not different (P > 0.05) between fish fed the two diets at 18 °C, but at 25 °C, we observed a higher ADC value in fish fed the FM diet than in those fed the SPC diet. ADC of protein was higher in fish fed the SPC diet than in the FM groups at either temperature. ADC of lipids was not different between the two groups at 25 °C but was found to be higher in fish fed the SPC diet than in the FM group at 18 °C. ADCs of energy and ash of the two fish groups remained constant at both water temperatures. Availability of phosphorus was significantly higher (P < 0.05) from fish meal based diets than from SPC based diets at both temperatures. A more striking effect of dietary protein source was found in the availability of calcium, which was lower in carp fed SCP based diets.

Chantier qualité GA; Sex ratios in farmed European sea bass are highly biased towards males (75 to 95%), which is problematic for aquaculture. In this mini-review, we re-analyse fisheries literature data about sex ratios in wild sea bass from 13 population samples, representing altogether 4889 individuals covering the major part of the distribution range of the species. We find that as a whole, the sex ratio of wild populations is biased towards females (59.4% females, p < 0.001), but that the sex ratio of the younger fish (

This preliminary study assessed genotype _ diet interaction in late growth of European sea bass (Dicentrarchus labrax) fed with either a ￠sh meal (FM)- or a ￠sh oil (FO)-based diet (M) or an all-plant-based (PB) diet. Atotal of 550 ￠sh from 224 families were reared together and tagged. DNAwas sampled and microsatellites were used to assign parentage. When ￠sh weight was 192 _ 54 g, two tanks were fed with M (FM: 100%; FO: 100%) and two others with PB (FM: 0% and FO: 0%). Body weight (BW), fork length (FL) and ￠llet lipid content (CorrFat) were analysed with a linear model and with REML methodology.We observed no signi￠cant di!erences between groups, but a slightly lower (P50.03) daily growth coe⁄cient in sea bass fed PB than in those fed M. Heritability estimates of BWdi!ered signi￠cantly from zero (PB: 0.37 _ 0.18; M: 0.47 _ 0.24). Sire _ diet interactions were signi￠cant and genetic correlations ranged between 0.51 and 0.87, showing genotype _ diet interaction for BWand CorrFat. For the ￠rst time, genetic parameters in the context of total replacement of marine ￠shery by-products were estimated in European sea bass, showing re-ranking of family performances with extremely contrasted diets.

Initiatives for the sustainable development of aquaculture have so far focused on the production of codes of conduct, of best management practices, of standards etc., most of which have been developed by international organisations, the industrial sector and non governmental organisations. They were, to a large extent, produced using a “top down” process and inspired by models from intensive industrial shrimp and sea fish farming (mainly salmon). However, most of global aquaculture production comes from small- and medium-sized farms, essentially in Asia which contributes 92% of the total world aquaculture production volume. The objective of this article is to define the contours of systemic typologies that are able to express the sustainability conditions of aquaculture systems. The proposed approach builds on surveys of aquaculture systems which differ in terms of their biogeographical nature (temperate/tropical and north/south countries) or their farming techniques and their governance systems. This work is a prerequisite to any attempt at an individualised and comparative evaluation of specific aquaculture systems from either global or territorial viewpoints. In order to go beyond the cleavage of a typology based on the differentiation between developed and developing countries, three typologies were produced. These typologies allow for discriminatory variables to be identified such as for example the marketing methods or the pace of innovation: a structural typology, a functional typology and a systemic typology. Finally, the representations of aquaculture activity and of its sustainability that producers have of the 4 different types that emerge from the systemic typology were recorded and analyzed., Les initiatives de développement durable de l’aquaculture ont jusqu’à présent surtout consisté dans la production de codes de conduite, de guides de bonnes pratiques, de standards, etc., élaborés pour la plupart d’entre eux par des organisations internationales, le secteur industriel et des organisations non gouvernementales. Ces documents ont largement été produits selon un processus de type « top down » et principalement inspirés par les modèles issus de l’aquaculture industrielle intensive de crevettes et de poissons marins (saumon principalement). Cependant, l’essentiel de la production de l’aquaculture mondiale provient d’exploitations de petite et moyenne taille, en Asie principalement qui contribue pour 92 % au volume total de la production aquacole mondiale. Cette étude vise précisément à définir les contours de typologies globales aptes à rendre compte des conditions de durabilité des systèmes piscicoles. La démarche proposée s’appuie sur des enquêtes réalisées sur des systèmes de production différenciés tant sur les plans de la biogéographie (pays tempérés et tropicaux, du nord et du sud) que des techniques d’élevage mises en œuvre et des modes de gouvernance de ces systèmes. Ce travail constitue le préalable à toute tentative d’évaluation à la fois individualisée et comparative de la durabilité de systèmes aquacoles spécifiques tant sur les plans systémique que territorial. Afin de dépasser le clivage d’une typologie basée sur la différenciation entre pays développés et en développement, trois typologies ont été produites. Elles permettent l’identification de variables discriminantes telles que par exemple le mode de commercialisation de la production ou le rythme des innovations mises en œuvre: une typologie structurelle, une typologie fonctionnelle et une typologie globale. Enfin, les représentations de l’activité piscicole et de la durabilité de celle-ci que se font les producteurs des 4 différents types ressortant de la typologie globale ont été recueillies et analysées.

International audience; This paper presents a non invasive, rapid and reliable way to quantitatively assess fin erosion in sea bass (Dicentrarchus labrax). The method is based on a visual assessment of fin profile and area loss of all fins except the anterior dorsal, on a scale from 0 to 4 in comparison with a perfect fin. The effects of stocking density (SD) and temperature on fin damage were investigated under experimental conditions (100-250 g fish). Over a 4-month period, mean erosion index (mean erosion level of all fins) was 10 times higher at 120 than at 20 kg m(-3), where most fins were undamaged. Damage was also dependent on time and oxygen concentration (35% lower at 53% O(2) saturation than at 105%). Fin condition was also affected by temperature: mean erosion index was 0.22-0.25 at 13-16 degrees C, but five times higher at 25 degrees C. Caudal and dorsal fins were always the most eroded. Fin damage was then monitored in a large land-based farm using high SD, and in a small sea cage farm operating at low SD. At the first site, 6 batches of two market size groups were examined: L (850-930 g, 50-80 kg m(-3)) and S (375-400 g, 42-60 kg m(-3)). Fin condition was good in all batches (mean erosion index, 1.1-1.3) and lowest at the highest SD. At the second site, four batches of large fish (350-890 g, 26-24 kg m(-3)) and four other groups below market size (100-270 g, 8-16 kg m(-3)) were examined. Fin erosion was the highest in large fish (mean erosion index, 1.1-1.2) and in the sea cages most exposed to climatic disturbances. In both sites, the most eroded fins were the caudal and dorsal. Differences in other external injuries were also observed between the two sites (less necrosis and more scale injuries in sea cages). The causes of fin damage are discussed in relation to metabolic and/or behavioral adaptations to rearing conditions and the main actions that could be taken to improve fin condition are discussed.

Heat shocks effective for the production of triploid brown trout (Salmo trutta ) were optimized: 28 °C shocks lasting 10 to 15 minutes and applied 5 minutes after fertilization induce very high rates of triploidy (close to 100%) without causing much mortality; they can therefore be proposed for mass production of triploid brown trout. Female homogamety in that species is also demonstrated from analysis of gynogenetic progenies and progenies of sex-inverted females. Although the efficiency of masculinizing hormonal treatments requires further improvement, production of all-female sterile populations is now possible in this species promising for European sea-farming.

International audience; An 84-day experiment assessed the combined effects of two fresh water quality levels (H: 1.71 +/- 0.15 mg O(2)l(-1) and 0.28 +/- 0.01 mg l(-1) total ammonia nitrogen (T-AN), L: 5.15 +/- 0.07 mg O2l(-1) and 0.54 +/- 0.01 mg T- AN l(-1)) and 3 stabilized stocking densities: 24.8 +/- 0.2, 74.2 +/- 0.5 and 120.0 +/- 0.9 kg m(-3)) on rainbow trout. Fish were fed using demand feeders with rewards proportional to stocking density. Mass increase was significantly affected by water quality and stocking density, being highest in H water and the lowest at 120 kg m(-3). There was no significant difference in final weight between 25 and 74 kg m(-3), but at 120 kg m(-3) it was 27% and 19% lower in H and L water respectively than at 25 kg m(-3). Feed intake (FI) from day 0-85 was significantly affected by water quality, 1.5% in H compared to 1.1-1.0 in L, but there were no significant differences in apparent feed conversion (AFC). FI was not significantly affected by stocking density but AFC was impaired, it increased with stocking density. Marked changes in fish morphology and composition were related to water quality: Condition K factor and fillet fat content were significantly higher in H than in L groups. Dorsal and pectoral fin condition was affected by stocking density and water quality: fins were significantly longer and less eroded in L groups and at low stocking density. Physiological measures were within the usual ranges, but differed between treatments. Changes in plasma osmolarity, hydromineral balance (Na(+)) and acid base balance (HCO(3)(-)) showed that fish were more affected by water quality than by stocking density. There was no sign of acute stress in acclimated fish as cortisol and glycemia were similar under all experimental conditions. This study highlights the importance of water quality and feeding conditions when considering the effects of stocking density on fish welfare.

The change in catches and mean size of one-year-old perch (Perca fluviatilis) in Lake Geneva was studied between 1957 and 2005, and related to trophic changes and average temperature. The status of Lake Geneva, assessed on the basis of total phosphorus concentrations, switched from being oligotrophic before 1960 to eutrophic, with total phosphorus concentration reaching nearly 90 µ gL −1 in 1976-1979. In response to management measures, the trophic status then returned to mesotrophy in the early 2000s. Zooplankton is the main food consumed by young perch, and quantities present (annual biovolumes of zooplankton) were recorded throughout the study period. The lake water tem- perature was also recorded. Data obtained from perch catches and perch spawns enabled eleven strong cohorts of perch to be identified. Strong cohorts dominated the stock for three years, until they were massively caught by fishermen. Yields have fluctuated widely, increasing rapidly until 1975, and subsequently decreasing, with an exceptional decline between 1976 and 1981. During the period 1977-1981, unfavourable climatic conditions in spring were probably the main cause of this fall in perch yields. For the other periods, perch yields and the mean size of one-year-old perch were significantly correlated with trophic parameters, total phosphorus concentration and zooplankton biovolume. Correla- tions are higher if only strong cohorts are taken into account. As a result of the re-oligotrophication process, perch growth has been progressively reduced, age at first maturity delayed and strong cohorts become less frequent; the mean size of 0+ individuals in strong cohorts is significantly smaller than in the other cohorts, suggesting a population density effect in the context of a limited supply of zooplankton. During the study period, trophic changes in Lake Geneva have had more impact on perch growth and yield than has temperature, since no significant correlation could be detected between water temperature and perch growth.

International audience; At the onset of sexual maturation, European eels Anguilla anguilla exhibit high locomotor activity which may correspond to migratory restlessness. We measured activity of captive eels and determined whether it correlated with downstream runs of silver eels as well as changes in environmental factors. Groups of eels at different stages of the silvering process (yellow to silver stage) were tagged and placed in separate tanks supplied with either river or tap water. Activity was measured by means of a flat-board antenna placed vertically in the middle of the tank at the surface of the water.Wild migrating silver eels were caught in the nearby river. Activity of eels in the river water tanks increased 1 to 2 days before downstream migrating eels were caught in the trap, and concurrently with a rise in turbidity and a decrease in conductivity. Activity of eels in the tap water tank showed a different pattern, which did not correspond to downstream runs. A peak in activity corresponded to a drop in tap water pH. It is concluded that eels do show periods of high locomotor activity at the onset of migration and this could be used to predict downstream migration. Movements are triggered by changes in water composition (as opposed to changes in discharge, atmospheric pressure and lunar cycle) measured using turbidity and/or conductivity as proxies. If eels are able to detect such small changes in water conductivity (80 μS cm−1), they may use it to find their way to the estuary.; Au tout début de leur maturation sexuelle, les anguilles européennes, Anguilla anguilla, présentent une forte agitation qui pourrait correspondre aux premiers mouvements migratoires. L'objectif de cette étude est de déterminer si ces périodes d'activité correspondent aux pics de dévalaison d'anguilles argentées en rivière et si elles peuvent être associées aux variations de certains facteurs environnementaux. Plusieurs lots d'anguilles (stades jaune et argenté) ont été marqués et placés dans des bassins séparés, alimentés soit en eau de la rivière, soit en eau de ville. L'activité des anguilles est mesurée par l'intermédiaire d'une antenne de détection située verticalement au milieu du bassin, près de la surface. Un piège de dévalaison permet de capturer les anguilles en migration dans la rivière. L'activité des anguilles en bassins alimentés par la rivière ont une activité accrue 1 à 2 jours avant la capture d'anguilles de dévalaison dans le piège et ces périodes correspondent à une augmentation de la turbidité et à une diminution de la conductivité. Les individus dans le bassin eau de ville présentent un comportement différent et l'unique pic d'activité correspond à une baisse du pH. En conclusion, les anguilles montrent bien des périodes d'activité intense au moment de la dévalaison et ceci pourrait être utilisé pour prévoir les pics de dévalaison. Les mouvements sont déclenchés par des variations dans la composition de l'eau de la rivière (par opposition à des variations de débit, de pression atmosphérique et au cycle lunaire) visibles à travers les changements de turbidité et/ou de conductivité. Si les anguilles sont capables de percevoir des variations aussi faibles de conductivité (80 μS cm−1), ceci pourrait constituer un signal pour l'orientation vers l'aval.

International audience; Fin condition was examined in 100–500 g hatchery-reared rainbow trout sampled in a large range of environmental conditions of an experimental farm. A method that is simple to use, requires little training, and does not need costly sophisticated equipment or reference to a model is proposed to assess fin erosion (defined as a decrease in size and profile alteration of fins). A procedure to reliably measure the length of the longest ray present in two selected fins (dorsal and pectoral) is described. Fin general profile is assessed using five levels of erosion based on the precise rank of intact or eroded rays to limit subjective bias. The suitability of the two descriptors of fin erosion under laboratory, farm or field conditions is discussed

The objective is to study different factors of variations in the body shape of trout (Salmo trutta ) belonging to the Mediterranean lineage (indigenous trout) or Atlantic lineage (introduced trout), and their hybrids. Using thin plate-spline (TPS) method by pointing landmarks, it made possible to provide a graphical representation of the characteristic conformation of the individuals. The characteristics of form highlighted let appear – that the male trout have a dorsal part more prominent than that of the female trout and a larger head – the existence of a general curvature of the body related to the size of trout, independently of the sex. In addition, characteristics of form provide satisfactory results to distinguish the Mediterranean lineage from the Atlantic lineage. The recognition of hybrid trout is more random because very near to Mediterranean trout. The existence of a sexual dimorphism could be established in spite of the absence of information on the sex. Comparative with the sexual dimorphisms in spawning period reveals morphological transformations during the reproduction, mainly for the males. Independently of the genotypic and sexual dimorphisms, a general curvature of the body related to the size was detected.

Lack of genetic differenciation between anadromous and resident sympatric brown trout (Salmo trutta) in a Normandy population. Aquatic Living Ressources

Evaluating the ecological impact of an oil spill is a complex issue requiring coherently articulated examination of the sequence of interactions that link the cell, where contaminants exert their effects, to the ecosystem, where interactions with human activities arise. This sequence of interactions traverses the frontiers between scientific disciplines (chemistry, toxicology, physiology, and fisheries ecology). Using the common sole (Solea solea L.) as a model species for the coastal habitats polluted by the "Erika" oil spill, our research project attempted to define indices of functional integrity that characterised the consequences of fuel exposure at the different biological levels. The coupling of field observations with experimental laboratory work revealed how functional alterations which are readily observable within individuals and their organs are progressively obscured as investigation progresses towards more complex organisational levels. Some of the approaches and indices are proposed as instruments for evaluating the impact of contamination by hydrocarbons., L'évaluation des conséquences écologiques d'une marée noire est un problème complexe qui requiert un examen articulé et cohérent de la chaîne d'interactions qui relie l'échelle cellulaire, à laquelle agit le contaminant, à l'échelle écosystémique, où se situent les interactions avec les activités humaines. Cette chaîne d'interactions traverse les frontières des disciplines scientifiques (chimie, toxicologie, physiologie, écologie halieutique). En prenant la sole (Solea solea L.) comme espèce cible - espèce caractéristique des habitats côtiers pollués par l'"Erika" - le programme de recherche ECTOPHY est une première tentative de mise en place d'une approche multidisciplinaire visant à définir, valider et mettre en relation des indicateurs d'intégrité fonctionnelle caractérisant les différents niveaux biologiques. Le couplage d'observations in situ avec des expositions en milieu contrôlé a montré que des pertes de fonctionnalité évidentes et durables à l'échelle de l'individu sont masquées à l'échelle de la population. Certaines des approches (in situ ou expérimentale) et certains des indicateurs testés peuvent être proposés comme instruments utilisables dans le cadre d'évaluation d'impact de pollutions par des hydrocarbures.

indexedcc; International audience; The Gambia Estuary is one of the last estuaries in West Africa not to have been affected by strong environmental changes and adverse human disturbances. In order to describe the spatio-temporal change in fish biomass in this estuary, and the seasonal changes in fish size classes, five research surveys have been conducted at characteristic periods in the river's water regime and meteorological seasons. The fish assemblages were sampled by two vertical echosounding protocols: mobile surveys (zigzag transects) in the estuary and moored stations. The two sampling methods produced a similar image of the fish assemblages in terms of the distribution of total biomass and target strength distributions. Large fish aggregations were detected in the most marine area at the end of the wet season, and fish biomass increased through the dry season in the upstream zone. Fish were smaller at the beginning of the wet season and they were always larger in downstream areas.

International audience

The individual growth variability of passive integrated transponder tagged sea bass was studied using data sets from two different experiments. In experiment 1 (n = 485), fish submitted to different photoperiod regimes were held in fourteen groups of individual weight of 88 ± 13 g (mean ± SD). In experiment 2 (n = 748, initial weight 243 ± 30 g) fish were held in fifteen groups and had either free or restricted access to diets with three lipid levels. After adjustment for treatment and tank effects, individual growth curves were analysed using multivariate analysis (principal component analysis and clustering) and were modelled using the summary statistics technique. Different growth profiles where characterized. All of them appeared to be curvilinear. They differed in their level (initial and final weight), slope (slope, specific growth weight, gain) and especially the ratio of males, which showed sexual growth dimorphism. The fish with similar initial weight proved to have very different growth performances, regardless of the treatment effect. Within the same sex, part of the variability between the growth profiles could be explained by differences in the social interactions and in the genetic potential of growth among individuals., La variabilité individuelle de croissance chez le bar est étudiée à partir de données provenant de deux expérimentations où les poissons ont été marqués individuellement avec des transpondeurs passifs. Dans l'expérimentation 1 (n = 485), les poissons, dont le poids initial était de 88 ± 13 g (moyenne ± écart type), sont soumis à différents régimes photopériodiques. Dans l'expérimentation 2 (n = 748, poids initial moyen = 243 ± 30 g), les poissons élevés dans quinze bacs reçoivent une alimentation soit en accès limité, soit en accès libre, combinés à trois taux de lipides alimentaires. Après ajustement des données de l'effet traitement et de l'effet bac, une typologie des courbes individuelles de croissance est réalisée par analyse de données multidimensionnelle (analyse en composantes principales et classification ascendante hiérarchique). Les courbes-types de croissance sont modélisées par la technique des variables résumées. Différents profils de croissance sont caractérisés. Ils sont tous curvilinéaires et diffèrent par leur niveau (poids initial et final), leur pente (pente, taux de croissance spécifique, gain de poids) et leur proportion de mâles, montrant ainsi un dimorphisme sexuel de croissance. Des groupes de poissons ayant un poids initial de même ordre de grandeur peuvent avoir des performances de croissance très différentes. Intra sexe, une partie de la variabilité entre profiles types de croissance peut être expliquée par des phénomènes de dominance et par des différences de potentiel génétique de croissance entre individus.

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The application of fisheries acoustics in shallow waters opens new fields of observation and allows new methods for abundance estimates. In this paper we deal with echocounting of migrating fish crossing the Beaucaire-Vallabregues lock, the first obstacle encountered on the Rhone, using a SIMRAD EY500 split-beam sounder, 70 kHz frequency. Two transducers sampled a section of water and evaluated approximately 35% of the lock section, based on a calibration sphere. The number of fish crossing the lock was calculated for each fish lock. Crossing data for the fish were recorded (dates, position, exit time). The present analysis did not allow the identification of the two major species that cross the dam: shad (Alosa fallax) and mullet (Mugil cephalus). The number of fish counted was positively correlated with the catches per unit effort (CPUE) by recreating fishermen below the dam and with increasing water temperature. © 2000 Ifremer/CNRS/INRA/IRD/Cemagref/Editions scientifiques et medicales Elsevier SAS hydroacoustic / target strength (TS) / Alosa fallax / Mugil cephalus / Rhone river / migrating fish / lock

The effects of dietary medium-chain fatty acids (MCFA) on survival, growth and fatty acid composition of first-feeding carp larvae were investigated in two 21-day feeding trials. In trial 1, one diet CO was supplemented with 10% coconut oil, two diets, M1 and M2 with 1.7 or 4.2% interesterified medium-chain triacylglycerols (MCT), and two other diets T1 and T2 with 1% tricaprylin and 0.7% tricaprin, or 2.5% tricaprylin and 1.7% tricaprin. The five diets were made isolipidic (18% of dry diet) with triolein and compared to a control diet without MCFA. With a low dietary level (1% of dry diet) of caprylic acid (C8:0), final survival and mean weight of larvae fed CO, M1 and T1 were not significantly different from those of control (68 +/- 6% and 62 +/- 8 mg, respectively). In contrast, with a high dietary C8:0 level (2.5% of dry diet), final survival and mean weight of larvae fed M2 and T2 were markedly decreased (23 +/- 2% and 40 +/- 8 mg, respectively), without effect of the form of supply. In trial 2, larvae were fed six diets with graded tricaprylin contents (from 0 to 10% in diet). Survival was not significantly affected but growth was decreased by C8:0 levels higher than 2% of dry diet. Fatty acid composition of larval total lipids revealed high levels of lauric and myristic acids in larvae fed coconut oil. Deposition of C8:0 and capric acid (C10:0) was low after MCT feeding, but depended of the form of supply, being higher with pure than with interesterified MCT. Relatively high amounts of C8:0 and C10:0 were recorded in total lipids of larvae fed 10% tricaprylin. It is concluded that high levels of caprylic acid decrease growth but that low levels are well utilised by carp larvae, irrespective of the form of supply., Les effets des acides gras à chaîne moyenne (AGCM) sur la survie, la croissance et la composition en acides gras des larves de carpe ont été étudiés dans deux expériences d'alimentation de 21 jours. L'expérience n°1 a testé un régime supplémenté avec 10% d'huile de coprah, deux avec 1,7 ou 4,2% de triglycérides à chaîne moyenne (TCM) inter-estérifiés et deux autres avec 1% de tricapryline et 0,7% de tricaprine, ou 2,5% de tricapryline et 1,7% de tricaprine. Les régimes ont été rendus isolipidiques (18% de l'aliment sec) avec de la trioléine et comparés à un témoin sans AGCM. Avec des faibles teneurs alimentaires (1% de l'aliment sec) d'acide caprylique (C8:0), les survies et croissances n'ont pas été différentes de celles du témoin. En revanche, avec un niveau élevé de C8:0 (2,5% de l'aliment sec), les performances ont été diminuées quelle que soit la forme d'apport. Dans l'expérience n°2, les larves ont été nourries avec six régimes ayant des teneurs croissantes en tricapryline (de 0 à 10%). La survie n'a pas été affectée alors que la croissance a été diminuée par des taux de C8:0 supérieurs à 2% de l'aliment sec. La composition en acides gras des larves a été affectée par la taille des larves et l'aliment distribué. L'huile de coprah a entraîné un dépôt important d'acide laurique et myristique dans les larves. Les dépôts de C8:0 et d'acide caprique (C10:0) consécutifs aux TCM ont été faibles mais néanmoins plus importants avec des TCM homogènes qu'avec des TCM inter-estérifiés. Des proportions de C8:0 et de C10:0 relativement importantes ont été retrouvées dans les larves nourries avec 10% de tricapryline. Des niveaux élevés d'acide caprylique dans l'aliment diminuent la croissance mais des niveaux plus faibles sont bien utilisés par les larves de carpe.

The effect of feeding time was studied in rainbow trout fed different dietary levels of fat. Fish were fed either 1 h after light on in the morning or 1 h after light off in the evening with a low energy diet (LE, 6 % lipid) or a high energy diet (HE, 23 % lipid). Regardless of the diet, apparent digestibility and post prandial protein synthesis were higher in fish fed in the morning than in those fed at the beginning of the night. In fish fed the LE diet in the morning, growth performance and nutrient retention efficiency tended to be higher than in those fed at the beginning of the night. In contrast, fish fed the HE diet in the morning had lower protein growth rate, protein content and protein retention efficiency than those fed in the evening. These results suggest that protein metabolism might be involved in the effect of feeding time on growth and that there is an interaction between the time of feeding and dietary level of fat on growth., L'effet de l'heure d'alimentation a été étudié chez la truite arc-en-ciel nourrie à différents taux de lipides alimentaires. Les poissons étaient alimentés soit le matin une heure après le début de la phase d'éclairement, soit le soir une heure après l'extinction de la lumière. Deux aliments étaient utilisés, l'un avait un taux d'énergie bas (LE, 6 % de lipides), l'autre un taux d'énergie élevé (HE, 23 % de lipides). Indépendamment de l'aliment, le coefficient de digestibilité apparente et le taux de synthèse protéique post-prandial était plus élevé chez les poissons nourris le matin que chez ceux nourris le soir. Chez les poissons nourris avec l'aliment LE le matin, la croissance et la rétention des nutriments avaient tendance a être plus élevés que chez ceux nourris en début de nuit. Inversement, les poissons nourris avec l'aliment HE le matin avaient une plus faible croissance protéique, un plus faible taux protéique corporel final et une plus faible efficacité de rétention protéique que ceux nourris le matin. Ces résultats suggèrent que le métabolisme protéique est impliqué dans l'effet de l'heure d'alimentation sur la croissance, et qu'il y a une interaction entre l'heure d'alimentation et le taux de lipides alimentaires sur la croissance.

International audience

The common dentex (Dentex dentex) is a sparid fish which is considered a suitable candidate for Mediterranean aquaculture. A seven-weeks feeding trial was conducted over the summer period with common dentex, sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax). All three species were fed to visual satiety with two practical diets with varying crude protein and crude fat levels (55 % protein, 9 % lipids; 46 % protein, 17 % lipids). The initial body weights were 8.2, 11.6 and 17.3 g for common dentex, sea bass and sea bream, respectively. In all cases, specific growth rates were not significantly affected by dietary treatment, but they varied among species (sea bass 1.7-1.8 %; sea bream 2.1-2.3 %; common dentex 3.1-3.2 %). When comparisons between fish species were made, we observed that the increase in growth rates was linked to a decrease of the whole body fat content, as a consequence of a greater utilisation of dietary lipids as energy substrates. Furthermore, in common dentex, the 17 % lipid diet was able to improve protein retention, but this diet effect was less significant in sea bream and sea bass. In contrast to sea bream, the 17 % lipid diet did not up-regulate plasma GH levels in common dentex, which provides additional evidence for a more efficient utilisation of dietary lipids., Le dentex est un sparidé reconnu comme ayant un potentiel aquacole en Méditerranée. Une étude comparative de croissance entre le dentex, la daurade et le bar a été réalisée. Les trois espèces (poids moyen initial: 8,2; 11,6 et 17,3 g respectivement pour le dentex, le bar et la daurade) ont été nourries à satiété avec deux régimes expérimentaux (55 % de protéines brutes avec 9 % de lipides ou 46 % de protéines brutes avec 17 % de lipides). Chez chacune des espèces, le taux de croissance spécifique (TCS) n'a pas varié en fonction du régime alimentaire. En revanche, une différence significative interspécifique a été observée (bar 1,7¿1,8 %; daurade 2,1¿2,3 %; dentex 3,1¿3,2 %) avec également une différence significative dans le dépôt lipidique corporel, reflétant des différences dans l'utilisation des apports énergétiques d'origine lipidique. L'effet de rétention de protéines par des lipides a été plus important chez le dentex que chez les deux autres espèces. Par ailleurs, contrairement à ce qui est observé chez la daurade, le régime riche en lipides n'induit pas une régulation de la sécrétion de l'hormone de croissance chez le dentex, indiquant aussi une meilleure utilisation des lipides alimentaires.

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 x 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 stockrecruitment relationship., Le modèle élaboré pour cette étude a pour objectif de mettre en évidence l'importance de l'échelle spatiale dans la détection de relations de densité-dépendance chez des populations de poissons à savoir si des relations stock-recrutement existant à un niveau local peuvent également être observées à une plus grande échelle. Pour cela, une population de poissons géniteurs a été simulée dans un environnement artificiel composé de 20 x 20 cellules hexagonales, la cellule représente l'échelle locale et l'environnement l'échelle globale. Cinq comportements migratoires ont été modélisés au cours de simulations successives: i) les géniteurs ne changent pas de cellule et se reproduisent dans la cellule où ils sont apparus ; ii) ils se déplacent vers une des huit cellules voisines ; leur choix étant aléatoire ; iii) ils se déplacent vers la cellule voisine la moins peuplée ; iv) ils se déplacent vers la cellule voisine la plus peuplée ; et v) ils se déplacent d'abord vers une des cellules voisines, puis vers la cellule voisine la plus peuplée. Quand tous les géniteurs ont migré, ils se reproduisent et meurent. Le recrutement a lieu à l'échelle locale. Dans chaque cellule, le nombre de recrues est déterminé par la même fonction stock-recrutement de Ricker qui prend en considération le nombre de géniteurs présents dans la cellule au moment de la reproduction. Les migrations aléatoires et les migrations vers la cellule voisine la moins peuplée permettent d'avoir une distribution homogène de géniteurs dans l'environnement. Cette homogénéisation entre les cellules induit une synchronisation entre les différentes populations locales et la possibilité d'observer une relation stock-recrutement à l'échelle de l'environnement entier. En revanche, pour les trois autres modes de migration, les géniteurs ne sont pas répartis de façon homogène. Les simulations montrent que les relations de densité-dépendance définies à un niveau local ne sont pas toujours détectables à un niveau global. Ces résultats prouvent que l'étude d'un système passe en premier lieu par une bonne définition de l'échelle spatiale d'étude.

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.

Des campagnes d'estimation du stock de poissons, utilisant des méthodes acoustiques, ont été réalisées dans la zone côtière du Sénégal sur des fonds inférieurs à 15 m, à partir d'un bateau de pêche sportive, au moyen d'un sondeur à faisceau scindé utilisé en mode vertical. Sur une courte échelle de temps, les structures spatiales des populations de poisson semblent stables. La quantité de poisson détectée est variable, mais on observe une relative stabilité des distributions des indices de réflexion des poissons individuels. L'utilisation des méthodes acoustiques dans ces zones peu profondes, les conséquences des comportements de fuite des poissons, ainsi que les stratégies d'échantillonnage sont discutées. (Résumé d'auteur)

The incorporation of various bulk agents by substitution of an equivalent amount of the basal mixture was studied in terms of protein digestibility, growth performance and body composition in European seabass (Dicentrarchus labrax) juveniles. During the growth trial, triplicate groups of 40 seabass (mean initial weight: 7.0 g) were grown in seawater (salinity: 35; temperature: 18 degrees C) over 60 days. Fish were hand-fed, three times a day, one of seven experimental diets. Bulk agents tested at 10 or 20 % level of incorporation were silica, cellulose and a natural zeolite (chabamin). Feeding rates were adjusted in proportion to the percent dilution of the control diet without bulk incorporation. The incorporation of the bulk agents, at a 10 and 20 % level, did not affect protein digestibility or growth performance. Dietary bulk incorporation reduced feed efficiency values, particularly at the 20 % incorporation level. However, this reduction was mostly caused by the dietary nutrient dilution of the bulk-incorporated diets, rather than by a negative effect of the bulk agents as dietary ingredients. In comparison to the control treatment, bulk incorporation at 10 and 20 % level did not affect protein retention values. When compared with the control diet, 20 % bulk agent incorporation changed the evacuation profile of faeces and increased faecal egestion time., L'effet de l'incorporation de divers agents liants alimentaires sur la digestibilité protéique, les performances de croissance et la composition corporelle sont étudiés chez le juvénile du bar (Dicentrarchus labrax). La croissance pondérale est suivie pendant 60 jours, durant lesquels des lots de 40 poissons (poids moyen initial: 7,0 g) sont élevés en eau de mer (salinité: 35; température: 18 °C). Les poissons sont nourris à la main, trois fois par jour. Des agents liants sont testés selon deux taux différents d'incorporation dans l'aliment (10 et 20 %): la silice, la cellulose et une zéolithe naturelle (chabamin). Les taux de rationnement ont été ajustés en proportion au pourcentage de dilution du régime témoin, sans incorporation de liants. L'incorporation à 10 et 20 % des divers liants n'a pas affecté la digestibilité des protéines ou les performances de croissance. L'utilisation des agents liants a entraîné une diminution de l'efficacité alimentaire, notamment avec les régimes comprenant 20 % de liants. Cependant, cette réduction est surtout due à la dilution des nutriments des aliments avec les liants et non à un effet négatif des liants proprement dits. La composition corporelle des poissons entiers, à la fin de la période expérimentale, n'est pas significativement affectée par les différents régimes alimentaires. Par rapport au régime témoin, l'incorporation à 20 % des divers agents liants a changé le profil d'évacuation des fèces et a augmenté le temps de transit digestif.

7 graph.; National audience

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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, flee 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 food intake 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., Cette synthèse donne un aperçu des hormones pouvant être impliquées dans le contrôle de la prise alimentaire des poissons et propose des voies d'action hypothétiques en se basant sur les connaissances acquises chez les mammifères. La plupart des effets observés résulteraient de quatre types de mécanismes, chaque hormone agissant par le biais d'un ou de plusieurs d'entre eux : (1) les hormones peuvent agir directement sur les noyaux du système nerveux central associés au comportement alimentaire, ou via les afférents du nerf vague ; (2) elles peuvent agir indirectement via le tube digestif en ralentissant le transit gastro-intestinal, ce qui conduit à une distension de l'estomac activant les afférents du nerf vague ; (3) elles peuvent agir indirectement au niveau du métabolisme intermédiaire via la mobilisation ou le stockage du glucose, des acides gras libres ou des acides aminés ; (4) elles peuvent modifier directement ou indirectement sur la sécrétion d'autres hormones impliquées dans le contrôle de la prise alimentaire. Certaines de ces hormones (CCK, PYY, glucagon, adrénaline) agissent à court terme en régulant le niveau d'ingestion et sont généralement inhibitrices. D'autres hormones (GH, TH et leptin) demandent plus de temps pour modifier le comportement de prise alimentaire et apparaissent comme des régulateurs du stockage énergétique. Cependant, les actions à court ou à long terme de ces hormones ne sont pas toujours très claires, comme cela est observé pour les glucocorticoïdes et l'insuline, et semblent dépendre de l'environnement métabolique et hormonal.

The objective of the study was to evaluate the capacity of rainbow trout to discriminate diets containing micro-granulated or powdered novel fluoroquinolone in comparison with a positive (containing sulfamerazine sodium) and a negative control (placebo). In a first trial, groups of trout had access to a self-feeder containing the placebo feed for 10 days, and then to one of the four feeds during another period of 10 days. Fish reduced their voluntary feed intake (VFI) by more than 50 % when they had access to the positive control, and by more than 20 % when they had access to feed containing micro-granulated premix. There was no significant decrease in VFI when the fish had access to feed containing powdered premix, but in this latter case, an increase in feed refusals was observed. In a second trial, the capacity of the trout to discriminate between two self-feeders containing different feeds was tested. During a first period of 10 days, all the feed hoppers were loaded with the placebo feed, to determine the feeder preference relative to any dietary-independent factor. In the following period of 10 days, fish had access simultaneously to the two medicated feeds. During a third period of 10 days, a validation of the results was attempted, using the placebo feed or the positive control in one of the feeders. It was shown that trout were able to discriminate between the two medicated feeds and that micro-granulated premix was better accepted than powdered premix. In addition, an increase in feed refusals was observed when the preferred feeder was loaded with feed containing powdered premix. It is concluded that this tested fluoroquinolone could decrease significantly VFI. The powdered premix was more detectable by the fish than the micro-granulated premix and led to some refusals., L'objectif de ce travail est d'évaluer la capacité de truites arc-en-ciel à distinguer deux aliments contenant une nouvelle fluoroquinolone incorporée sous forme de micro-granules ou de poudre en comparaison avec un aliment témoin (contenant de la sulfamérazine) ou un contrôle (aliment placebo). Dans une première expérimentation, des groupes de truites ont accès à un distributeur à la demande contenant l'aliment placebo durant 10 jours, puis à l'un des quatre aliments durant une période successive de 10 jours. Les poissons réduisent leur consommation volontaire d'aliments de plus de 50 % lorsqu'ils ont accès à l'aliment témoin, et par plus de 20 % lorsqu'ils ont accès à l'aliment contenant l'antibiotique préparé sous forme de micro- granulés. Il n'y a pas de diminution significative de la demande d'aliments lorsque celui-ci contient l'antibiotique en poudre, mais dans ce cas la quantité d'aliments non consommés augmente. Dans une seconde expérimentation, la capacité des truites à différencier deux distributeurs d'aliments contenant les deux différentes formulations d'aliments médicamenteux a été testée. Durant une première phase de 10 jours, tous les distributeurs contenaient de l'aliment placebo, afin de déterminer la préférence éventuelle des distributeurs en relation avec des paramètres indépendants de l'aliment lui-même. Puis durant une seconde période de 10 jours, les poissons ont accès simultanément aux deux aliments médicamenteux. Enfin, durant une ultime période de 10 jours, une validation des résultats est tentée, en utilisant l'aliment placebo ou l'aliment témoin dans l'un des deux distributeurs. On montre ainsi que les truites sont capables de distinguer les deux aliments médicamenteux, et que l'incorporation de l'antibiotique sous forme de micro-granules est mieux acceptée par ces dernières que l'incorporation sous forme de poudre. De plus, une augmentation des aliments refusés est observée lorsque le distributeur d'aliments le plus utilisé par le groupe de truites est utilisé pour l'aliment contenant l'antibiotique incorporé sous forme de poudre. En conclusion, la fluoroqui- nolone diminue significativement la consommation volontaire d'aliments, et la préparation en poudre est plus facilement détectable par le poisson que la préparation sous forme de micro-granules.

High energy extruded diets were formulated to contain the same level of protein supplied either by soy protein concentrate (SPC) or fish meal. Three experiments were performed in order to measure voluntary feed intake and feed waste, faecal losses and soluble losses of nitrogen and phosphorus in rainbow trout (average body weight: 100 g). Voluntary feed intake and growth performance of fish fed with demand feeders were not different when diets contained 0, 50 or 75 % SPC instead of fish meal. Total replacement of fish meal by SPC led to a significant decrease in feed intake and resulted in poor growth. This was partly due to methionine deficiency in the SPC based diet. With the addition of crystalline DL-methionine in the diets, an improvement of feed intake and growth performance was apparent. Protein digestibility was high, regardless of the protein source. Excretion of ammonia and urea increased with the level of SPC in the diet. Nitrogen losses decreased when methionine was added to the diet containing only SPC as a protein source. Availability of phosphorus increased with the level of SPC in the diets. Daily soluble losses were not affected by the dietary treatments but the pattern of phosphorus excretion after feed intake was modified. The rise in soluble phosphorus in water occurred later when fish were fed diets with soy protein whatever the dietary level of soy protein concentrate., L'objectif de l'étude était d'évaluer les effets du remplacement partiel ou total de la farine de poisson par du concentré protéique de soja sur la consommation volontaire de nourriture et les pertes fécales et métaboliques d'azote et de phosphore chez la truite arc-en-ciel (poids moyen: 100 g). La consommation d'aliment et les performances de croissance des poissons nourris par des distributeurs d'aliment à la demande n'ont pas été affectées jusqu'à un taux de substitution de 75 %. Le remplacement total de la farine de poisson par le concentré protéique de soja a conduit à une faible croissance résultant d'une baisse significative de la consommation d'aliment. La supplementation en DL-méthionine sous forme cristalline a permis d'améliorer les performances de croissance grâce à une augmentation de l'ingestion d'aliment. La digestibilité des protéines était élevée pour tous les régimes, quelle que soit la source protéique. L'excrétion d'azote ammoniacal et d'azote uréique a augmenté avec le taux de concentré protéique de soja dans l'aliment. La supplementation en methionine de l'aliment contenant le concentré protéique de soja comme seule source de protéine a permis de réduire les pertes métaboliques d'azote. La disponibilité du phosphore a augmenté avec le taux de concentré protéique de soja de l'aliment. Le remplacement partiel ou total de la farine de poisson par le concentré protéique de soja n'a pas affecté la quantité de phosphore soluble excrété par jour; en revanche, le profil postprandial d'excrétion a été modifié.

Nutritional strategies and management of aquaculture waste; International audience

Short-term storage over several days as well as cryopreservation of turbot (Scophthalmus maximus) sperm were studied. Two extenders, Ringer 200 and artificial seminal liquid (ASL2), are suggested for semen collection in order to avoid the deleterious effect of urine contamination, and for the purpose of short-term storage between 0 and 15 degrees C. Oxygen atmosphere is not suitable for turbot sperm storage. Turbot spermatozoa undergo cryopreservation with a high rate of success especially in a sucrose solution with 10% dimethyl sulfoxide (DMSO) and 10% egg yolk.

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.

The incorporation of an attractant mixture by substitution of an equivalent amount of basal dietary mixture was studied in terms of feed intake and growth performance in European seabass juveniles (mean initial weight : 17 g) fed plant-protein rich diets during 21 days. Three diets had as main protein sources; fish meal, or one of two soy protein concentrates (S and E). To the basal mixture of these last two diets, as well as to a corn-gluten based diet, an attractant amino acid mixture was added at a 2.5% level. Daily feed intake was measured throughout the experimental period. Feed intake and weight gain were highest in seabass fed the fish meal based diet. In those fed the soy protein concentrate diets, the addition of the attractant mixture improved growth significantly; voluntary feed intake and feed efficiency were also ameliorated in these groups. In terms of growth, feed intake and protein utilisation, lowest values were found in fish fed with the corn-gluten rich diet, supplemented with the amino acid mixture.

L'efficacite de differents analogues du GnRH et/ou du pimozide pour induire l'ovulation chez l'omble chevalier est etudie a deux temperatures: 5°C, une temperature propice pour l'ovulation spontanee de l'omble chevalier et 10°C, une temperature inhibant l'ovulation chez l'omble chevalier. A 5°C tous les differents analogues du GnRH etudies sont capables d'induire et de synchroniser les ovulations. A 10°C, une preparation a diffusion prolongee du D-Trp 6 LH-RH a 20 μg.kg -1 et une forme a diffusion instantanee du D-Arg 6 sGnRH a 100 μg.kg -1 sont capables d'induire l'ovulation chez 80 % des femelles en une quinzaine de jours (contre 2 % chez les temoins). Le pimozide seul ou associe a une faible dose de D-Arg 6 sGnRH est capable d'induire quelques ovulations a 10°C, suggerant qu'une inhibition de type dopaminergique de la secretion gonadotrope puisse sc produire a 10°C. La survie des oeufs provenant des poissons traites au GnRHa a 5°C est comparable a celle des temoins (73 % ) excepte dans le groupe des poissons traites avec du GnRHa associe a du pimozidc (45 %). A 10°C, la survie des oeufs est significativement inferieure a celle des temoins a 5°C, sauf dans le groupe de poissons traites uniquement au pimozide. Aux deux temperature, la survie des oeufs de chaque ponte est correlee negativement avec la teneur en gonadotropine plasmatique de la femelle genitrice (valcur maximale observee dans les quatre jours suivant le traitement), sauf dans les groupes recevant la preparation a diffusion prolongee du D-Trp 6 LH-RH.

Le sperme testiculaire et celui contenu dans les canaux deferents, divises en trois ou quatre parties, ont ete collectes sur 4 a 6 mâles de truite arc-en-ciel de souche hivernale, environ toutes les deux semaines pendant trois mois (Janvier a Mars). Le volume de sperme, le spermatocrite, la motilite des spermatozoides, les concentrations en 11-ketotestosterone (11-KT) et en 17α-hydroxy,20β-dihydroprogesterone (17,20P), ainsi que la composition ionique, ont ete determines. Les deux steroides et les ions ont aussi ete mesures dans le plasma sanguin. Les concentrations en K + et en steroides dans le fluide seminal de chacune des parties des canaux deferents n'ont pas varie significativement pendant la periode etudiee. Dans deux parties sur trois des canaux deferents, les concentrations en Na + (parties I et III), en Ca 2+ (parties I et III) et en Mg 2+ (parties I et II) etaient significativement plus elevees a la fin Mars que deux mois plus tot. La motilite des spermatozoides testiculaires etait maximale (42%) a la mi-Fevrier, tandis que celle des spermatozoides des canaux deferents restait stable pendant les trois mois (80 a 100%). Il a ete confirme que le fluide seminal et le plasma sanguin sont isotoniques (300 mmol/kg). Les concentrations en K + , Na + , Ca 2+ , 11-KT et 17,20P dans le plasma sanguin et le fluide seminal differaient significativement (respectivement 0,3 et 34 mmol, 134 et 116 mmol, 3,4 et 2,0 mmol, 87 et 17 a 39 ng/ml, 11 et 3 a 13 ng/ml). Les concentrations en Na + et en steroides dans les deux milieux etaient correlees. L'osmolarite et les concentrations en Cl - , Na + , K + , Mg 2+ and Ca 2+ restaient constantes tout au long du tractus genital. Par contre, le spermatocrite et les concentration en 11-KT et en 17,20P diminuaient progressivement des testicules a la partie posterieure des canaux (respectivement 97 a 49%, 39 a 17 ng/ml, 13 a 3 ng/ml), alors que la motilite des spermatozoides (pourcentage de cellules mobiles et duree de la motilite) augmentait (74 a 96% et 41 a 51 s). Il n'a pas ete trouve de correlation significative entre la motilite des spermatozoides et les parametres physicochimiques du fluide seminal.

Les Siluroidei sont connus pour avoir, en milieu naturel, une activite trophique essentiellement nocturne. Ceci a ete confirme au cours d'experiences realisees en conditions d'acces constant a une source de nourriture, ou encore a l'aide de distributeurs d'aliments a la demande. Cependant, en conditions limitantes en temperature ou en oxygene, l'activite trophique de certains Siluroidei devient dependante de ces deux facteurs, et n'est plus synchronisee par l'alternance jour/nuit. Le rythme nycthemeral d'activite trophique des especes etudiees presenterait donc une acrophase preferentiellement nocturne, mais possederait une certaine plasticite. L'existence d'un controle d'origine endogene de ce rythme est aussi discute. Rares sont les poissons Siluroidei qui refusent de s'alimenter lors de distributions diurnes d'aliments. Il convient d'evaluer les consequences que pourraient avoir sur la croissance des horaires d'alimentation non synchrones avec les rythmes alimentaires. L'effet de l'heure des repas sur les performances de croissance montrent une tendance generale a une croissance superieure chez les animaux nourris de nuit par rapport aux animaux nourris de jour. Cependant, le mode de distribution choisi (en repas ou en continu) semble avoir plus d'influence que l'heure de distribution sur les performances de croissance. Certains auteurs ont aussi montre une augmentation de l'adiposite des poissons lorsqu'ils n'etaient pas nourris en phase avec leur rythme alimentaire.

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