Two groups of sea bass (mean initial weight 78 and 250 g) were given for 23 weeks a commercial diet, whose composition was modified or not (control). The modified diet was: — supplemented with highly oxidized fish oil, — poorly supplemented with ascorbic acid, — not supplemented with butylated hydroxytoluene, DL-alpha-tocopheryl acetate and choline. At the end of the experiment, fish fed the modified diet displayed skeletal muscle degeneration, decreased red blood cell count, haemoglobin content and haematocrit, and increased crythrocyte fragility and plasma enzyme activity (aspartate aminotransferase and creatine kinase). Simultaneously, low DL-alpha-tocopheryl acetate levels and increased amounts of thiobarbituric acid-reactive substances were observed in muscle and liver. On the other hand, growth disorders, liver lesions, changed plasma enzyme activity (alanine aminotransferase, glutathione peroxydase), or altered conjugated dienes in perivisceral fat were not evidenced. The pathological observations were more pronounced on the smaller fish group, but the disease could already be detected by measuring haematological and biochemical criteria, the interest of which in the diagnosis of such nutritional disease is discussed.

Les poulamons de la rivière Sainte-Anne frayent dans un secteur de rapides, situé à environ 7 km de la confluence avec le fleuve Saint-Laurent, et probablement aussi dans un secteur d'accumulation de frasil généré par ces rapides. Les variations interannuelles dans la dérive des œufs et des larves de poulamon, à différentes stations dans la rivière, sont reliées aux conditions annuelles de température de l'air et de débit. Des températures et débits bas et stables ont causé la rétention des œufs et des larves dans la partie amont du secteur d'étude (1980–1981, 1981–1982); les températures et débits plus élevés et variables ont causé une dérive régulière au fleuve Saint-Laurent de janvier à avril (1982–1983). En 1980–1981, une hausse soudaine de la température et du débit a causé une avalaison massive des œufs au Saint-Laurent durant la seconde moitié de février. Des œufs de poulamon sont retenus et incubés dans le frasil, qui s'accumule en un barrage suspendu pouvant s'étendre, selon les années, sur plus de 3 km de rivière. Peu de temps après la fraye, la densité moyenne d'œufs par 2 l de ce substrat, sur l'ensemble du barrage suspendu, atteignait 228 en 1981 (19 janvier), 235 en 1982 (6 février), et 54 en 1983 (15 février). Les variations interannuelles dans la distribution spatiotemporelle des œufs dans le frasil concordent avec celles suggérées par les résultats de la dérive.

L'estimation de l'âge de Prochilodus nigricans Agassiz, 1829 est réalisée à partir de 840 poissons pêchés de 1983 à 1987 dans les principaux milieux du réseau hydrographique de la rivière Mamoré (Béni, Bolivie). Diverses préparations et observations de pièces calcifiées (écailles, otolithes, rayon épineux dorsal et os operculaire), ainsi que les comparaisons de plusieurs lectures, ont permis de choisir l'écaille et ses marques de croissance pour estimer l'âge. Les pertes d'écailles, entraînant la présence de très nombreuses écailles régénérées macrocentriques, paraissent dues à l'abondance des poissons lépidophages du genre Roeboides. Les marques principales de croissance sur les écailles microcentriques sont décrites, ainsi que les principales anomalies ayant engendré des difficultés de lecture. La validation des marques retenues est faite directement par la mesure de la distance séparant la dernière marque du bord de l'écaille, et indirectement, pour les jeunes nés dans l'année, par la comparaison de leur distribution de longueurs à la capture avec celle obtenue par rétrocalcul au moment de l'apparition de la première marque, Pour tous les groupes d'âge, la formation des marques principales de croissance sur les écailles est influencée par le niveau des eaux dans le Mamoré : la formation des annulus se produit une fois par an lors de l'étiage ou au début de la crue (septembre à décembre), sur une grande majorité des individus. La date moyenne de naissance étant fixée au 15 février, l'âge peut étre connu en général avec une précision de l'ordre du mois. Pour l'étude de l'âge chez une espèce inconnue, le choix préliminaire du type de pièce à prélever est orienté â la fois par les résultats des tests de lectures comparées et par des considérations pratiques.

Seasonal variability in the morphology of the digestive tubules was investigated by means of a morphometric procedure in a population of Littorina littorea (Mollusca, Gastropoda) collected from the Abra estuary (Bay of Biscay, Basque Country) at four different seasons September, December, May and July). Some biometric characteristics of the winkles were recorded throughout the study period. Size parameters did not change significantly but high values of flesh condition (wet weight of flesh in mg per wet shell weight in g) were recorded in December and the lowest values in May. The reproductive state was determined using a planimetric procedure to calculate the relative tissue volume of digestive gland, gonad and storage tissue in the visceral mass. The relative volume of the digestive gland was significantly reduced in May. Gonad tissue volumes were maximal in May and minimal in September. Reserve connective tissue reached a maximum value in September. The quantitative structure of the digestive tubules was also investigated. The following five parameters were used to quantify digestive tubule morphology: mean epithelial thickness (MET), mean diverticular radius (MDR), mean luminal radius (MLR), MLR/MET ratio and MET/MDR ratio. The seasonal changes in the tissue composition of the visceral mass do not affect significantly any of these parameters. Thus, reserve storage/consumption and gamete development did not appear to affect the morphology of the digestive tubules in winkles. Reduced MET and MET/MDR values and augmented MLR/MET values were, however, observed at the breeding-spawning period. Such changes resemble a general stress response which might be related to the high metabolic cost of this phase of the reproductive cycle.

Fish assemblage structure of 29 Brittany streams is examined. Catchment area, stream gradient, and distance from sources are significantly correlated with species richness. Addition of species with increasing stream size occurs for all streams with no evident longitudinal replacement, suggesting little discontinuity in the stream geomorphology or temperature. Total density of fishes decreases significantly with an increase in stream size but no relation was found between total biomass and catchment area. Headwaters are characterized by short-lived, solitary, and nocturnal feeding species, whereas downstream sites are characterized by long-lived, schooling, diurnal feeding species. Presence of solitary and nocturnal feeding species upstream could be related to predation and/or competition factors. Temporal variation of individual species density varies from an upstream-downstream gradient with the highest variation upstream. Species responsible for this variation were mostly small benthic ones relatively difficult to sample, therefore, the greater temporal variation in upstream areas could be attributed to a deficiency of the sampling methodology.

Les teneurs en mercure de plusieurs espèces de poissons sont expliquées en utilisant un modèle présenté antérieurement par Thomann (1981), basé sur le transport des contaminants en milieu marin et leur transfert à travers les chaînes alimentaires aquatiques. Il est montré en particulier que les facteurs environnementaux liés au processus de méthylation du mercure qui se déroule dans la colonne d'eau et à la surface des sédiments, peuvent être responsables des teneurs particulièrement élevées decertaines espèces. Notre interprétation originale de teneurs en mercure de nombreuses espèces de poissons de l'Atlantique pêchés entre 1971 et 1980, est accompagnée de la présentation de "concentrations de référence" qui peuvent être d'utilité pour établir des comparaisons avec d'autres valeurs comme par exemple les teneurs d'autres poissons capturés à une autre époque ou dans d'autres régions.

Ammonium and nitrite oxidizing bacteria were enriched in separate cultures using a primary inoculum of water from an enclosed shrimp rearing facility. Each enrichment was continued by transfer to increasing volumes of medium up to 151. Seventy four strains of heterotrophic bacteria were isolated; seventeen from each primary inoculum, and twenty from each of the 151 enrichments at the time when all the ammonium or nitrite had been utilized. All the isolates, described by 101 characters, were subjected to numerical taxonomy. During the enrichment for ammonium oxidizers, astrong selective pressure led to the disappearance of some strains, mostly enterobacteria. Two taxonomic groups composed of pseudomonads and asporogenous Gram positive rods were associated with the ammonium oxidizers. The population was characterized by an inability to use amino acids as carbon and energy sources. In contrast, the strains associated with nitrite oxidizers were able to use all the carbon and energy sources tested. Many of these strains were Gram positive, asporogenous aerobic rods, others were Gram negative pseudomonads.

The larval stages of Anguillicola crassus, a parasite of the swimbladder of eels, are described, using light and scanning electron microscopy. Second-stage larvae in copepods are characterized by a globular cephalic end and third- and fourth-stage larvae by an apical selerotized ornamentation consisting of two U-shaped median pieces. Third- and fourth-stage larvae are difficult to distinguish from each other using light microscopy because the third moult has never been observed and there are no obvious characters differentiating the two stages. Three characters, however, observed by using high magnification of light and scanning electron microscopy are considered as distinctive between the two stages, namely presence or absence of deirids and lateral alae and differences in the structure of the cuticle. These morphological characters will permit epidemiological studies at the larval level.

It is difficult to apply sanitary standards for mollusc contamination by paralytic shellfish poisoning to animals not consumed whole. This problem is illustrated by the 1990 embargo on a Japanese shipment of frozen scallop muscle and gonad: the sanitary threshold applied to digestive gland (in Japan) does not guarantee that muscle and especially gonad are toxin-free. Accordingly, we performed experimental contaminations of scallops (Pecten maximus) from Port-en-Bessin (Normandy, France) using a toxic Japanese strain of Alexandrium tamarense. During the contamination/decontamination experiment on different tissues (digestive gland, muscle, gonad), extracts were obtained using cold acetic acid 0.1 N to maintain the perfect integrity of the toxin profile. These initial trials indicated that with a daily concentration of 2 × 106 cells. 1-1 a maximum toxicity equivalent to 850 μg.100 g-1 of digestive gland meat was attained in 2 weeks. Concerning toxin profiles, it would appear that gonad can selectively accumulate gonyautoxins, particularly GTX2/GTX3, even though the relative amount of uptake always follows the order hepatopancreas > gonad > muscle. Morcover, studies of Japanese scallops imported in 1990 showed that 80% of the gonad and muscle samples included all or part of the kidneys and excretory organs, whose relationship with gonad toxicity need further clarification. Finally, the toxin profile of the different organs during decontamination revealed an inversion of the relative proportions of GTX2/GTX3 epimers, as noted by other authors. Confirmation of selective biological conversion between organs will require further study.