An estuary is an ecotone. It plays various vital roles in the functioning of the different fish species encountered. Each estuary has its own geographical, hydraulic, sedimentological and biological characteristics. These specific features influence the makeup and structure of the fish assemblages and the dynamics of the fish populations. The Gironde estuary is the biggest estuary in France and one of the largest in Europe. It is considered to be relatively unspoilt. The aim of this study is to provide an initial reference document on the specific composition of its fish assemblage. This study establishes a list of the fish species sampled by two different and complementary methods which have been regularly undertaken since 1979. A typology is recognized according to a series of ecological criteria. The relative proportion of fish species that spend all their life cycle in the Gironde estuary is very small. Moreover, the Gironde would appear to be the European estuary with the largest migratory amphihaline fish assemblage. Considering the study made by Elliott and Dewailly (1995), the Gironde estuarine fish population can be compared to those of 17 other European estuaries. The classification we obtained, raised a number of questions on the particularities of estuarine environment, with regard to ecological diagnostics and comparisons. Important points include the need for an inter-calibration of sampling practices, the relevance of taking into account the physical dimension of the environment (tidal range, upstream limit of saline intrusion, etc.), the degree of anthropogenic influence and its evolution.

La diversité spécifique est généralement considérée comme un facteur-clé de la résilience des écosystèmes en réponse à la pression anthropique et notamment à la pression de pêche. Dans cet esprit, on analyse ici l’impact de la pêche sur la diversité spécifique, à partir du cas des ressources démersales côtières de Guinée. Celles-ci ont la particularité d’avoir subi récemment un très rapide et important accroissement de la pression de pêche. En une quinzaine d’années, on est ainsi passé d’une situation dans laquelle les ressources démersales étaient considérées comme étant « à l’état vierge », à une surexploitation globale. Cette évolution mérite d’être considérée comme un « modèle accéléré » de l’histoire d’une exploitation. L’analyse se fonde sur les données de 18 campagnes scientifiques de chalutage démersal effectuées dans la zone côtière guinéenne entre 1985 et 1992. Le niveau de diversité spécifique, par campagne ou par trait de chalut, est quantifié par des indices synthétiques : la richesse spécifique, la diversité de Shannon et l’équitabilité. Les indices par trait de chalut sont analysés par les méthodes de modélisation en analyse de variance, afin de dégager une évolution temporelle des indicateurs. Les diagrammes rang/fréquence de chaque campagne sont également établis. On montre que les indices de diversité et d’équitabilité restent sensiblement constants, alors que l’abondance et la richesse spécifique diminuent significativement au cours de la période. Les espèces les moins abondantes et particulièrement des espèces de la communauté à Sparidés, tendent ainsi à disparaître des prélèvements. Enfin, l’année 1989 présente des indices de diversité faibles, liés à des conditions environnementales favorables pour certaines espèces entraînant un recrutement exceptionnel de celles-ci. La pertinence des indices utilisés est discutée.

We tested the hypothesis that along with gill Na+K+ATPase activity reduction, branchial energetic metabolism of brook charr (Salvelinus fontinalis) is altered during sexual maturation. Maturing and sterile fish were transferred from freshwater (FW) to seawater (SW). The activity of gill pyruvate kinase (PK), cytochrome C oxidase (COX), citrate synthase (CS) and lactate dehydrogenase (LDH) was measured at different intervals. Following 1 month in SW, twofold increases in Na+K+ATPase activity were recorded in all groups, while mean metabolic enzyme activities were sharply reduced (COX: 0.051 ± 0.029 to 0.036 ± 0.018; PK: 1.670 ± 0565 to 1.210 ± 0.340 LDH: 2.245 ± 0.690 to 1.642 ± 0.381 μmol mg–1 protein min–1). Interestingly, during this period, no mortality occurred. After 5 months, comparison of Na+K+ATPase:CS and Na+K+ATPase:LDH ratios of mature and sterile fish held either in FW or SW, indicated that the response of Na+K+ATPase largely exceeds the response of the metabolic enzyme apparatus in hyperosmotic conditions. Hence, the reduced iono-osmoregulatory capacity and higher mortality observed in SW-maturing fish during the reproductive season appears to be mainly attributable to Na+K+ATPase activity reduction rather than the alteration of gill metabolic capacity, since no concurrent increase of metabolic enzyme activity with Na+K+ATPase activity occurred.

The histological development of the digestive tract in hatchery-reared green sturgeon (Acipenser medirostris) larvae and the effects of food deprivation on the digestive system organization were studied from hatching until 31 days post-hatching (dph). At hatching, the larval digestive system consisted of two rudiments: a large endodermal yolk sac and a primordial hind-gut. During the endogenous feeding phase, the wall of the yolk sac differentiated into the stomach (glandular and non-glandular regions) and the anterior and intermediate intestine, while the hind-gut primordium differentiated into the spiral valve and rectum. At the onset of exogenous feeding (15 dph at 16 °C), the organization and cytoarchitecture of the digestive system in green sturgeon larvae was generally similar to those of juveniles and adults. Larvae deprived of food exhibited a progressive deterioration, with subtle pathological changes observed after 5-d starvation: shrinkage of digestive epithelia, tissue degeneration, and necrosis were observed at 10–15 d of starvation (30 dph). No changes were observed in the mucous secretion of different regions of the digestive tract of food-deprived larvae. The histological analysis of the larval digestive system may be used to evaluate the nutritional condition of larval green sturgeon in their nursery habitats in spawning rivers, which are affected by dams and flow diversions.

In Eurasian perch (Perca fluviatilis), females grow significantly faster than males. Moreover, gonadal development has a significant negative impact on somatic growth and fillet yield. In order to induce sterility, triploidy induction was attempted by subjecting fertilised eggs to heat shocks. Different combinations of temperature (28, 30, 34, 35 and 36 °C), duration (2, 5, 10 and 25 min) and time of shock initiation (TI = 3, 5 and 7 min post-fertilisation) were tested. Flow cytometry analysis was used to assess ploidy level of control and heat-shocked larvae. Low intensity (28–30 °C) and long duration (10 and 25 min) shocks lead to significantly higher survival (44 ± 26%) and triploidisation (71 ± 26%) rates than high intensity (34–36 °C) and short duration (2 and 5 min) shocks (17 ± 19% and 21 ± 26%, respectively). The most effective conditions for efficient triploidy induction were low intensity shock of 30 °C, applied 5 min post-fertilisation for 25 min. This treatment led to the production of all-triploid populations (100%) with up to 43% survival rate.

Among the gastropods, some muricid shells are composed of an inner aragonitic crossed lamellar layer and a calcitic prismatic outer layer. The analysis of the structure and composition of the two layers of Concholepas shows that the crossed lamellar layer is similar to those of other Mollusc taxa. Sr, Mg and S contents are low in both layers. According to infrared spectrometry, the organic content of the outer calcitic layer is higher than that of the aragonitic crossed lamellar layer. The study of the nanostructure allows for the proposal of a new 3D interpretation of the fine structure of the crossed lamellar layer. The calcitic prismatic layer is compared with the outer calcitic prismatic layer of an archaeogastropod genus: Haliotis.