An ultrasonic tagging program for tuna was conducted in 1988 and 1989 within the Regional Tuna Project of the Indian Ocean Commission. Three yellowfin and six skipjack tuna were tagged with temperature or depth sensitive transmitters in the North-western part of the Mozambique Channel (12°S-44°E) around Anjouan island (Comoros Archipelago) where several fish aggregating devices (FADs) were previously moored. The horizontal and vertical movements observed during 8 tracks (3 yellowfin and 5 skipjack tuna) whose duration was between 3 and 24 hours, are analysed in terms of swimming depth, temperature encountered and position of the tracked tuna relative to the FAD or coast line. Comparison between recorded depth of tracked tuna and echo sounded fish indicated tracked tuna were schooling. Two of the 3 tagged yellowfin tuna displayed a behaviour of association with FADs. The optimal distance between 2 anchored FADs, to avoid adverse interference in the attraction of tuna, is estimated as 11 nautical miles. A very small percentage of time is spent by yellowfin tuna near the surface. The mean swimming depths encountered in the daytime by yellowfin tuna are much deeper (70-110 m) than they are at night (40-70 m). The relative homogeneity in the observed behaviour of yellowfin tuna and the fair general agreement with previous results obtained in the Pacific Ocean, should allow application of ultrasonic tagging results to fishing and prospecting purposes in the future. The movements of the 5 tracked skipjack tuna do not indicate a behavioural association with FADs, and do not present marked differences between the swimming depths encountered by night and during the daytime. The high variability observed in the behaviour of the different tracked skipjack tuna, and the bad agreement with previous results obtained in the Atlantic and in the Pacific Oceans have to be emphasized. A high turnover of the skipjack tuna concentrated around FADs due to an intense and pelmanent migratory flow through the area of Comoros Islands could partly explain these apparent discrepancies.

Il est bien connu des pêcheurs que les monts sous-marins, nombreux dans l'Atlantique tropical est, concentrent parfois de fortes biomasses de thons. Cette association thons et monts sous-marins n'a paradoxalement fait l'objet d'aucun programme de recherches. Le présent article fait un bilan des captures de thons réalisées par les flottilles thonières internationales sur les monts sous-marins connus dans l'Atlantique tropical est durant les années récentes (période 1980 à 1987). La prise annuelle de thons sur certains monts sous-marins peut atteindre plusieurs milliers de tonnes. Les statistiques de pêche thonière montrent que certains monts sous-marins sont riches en thons, alors que d'autres semblent pauvres en permanence, bien qu'ils soient situés dans des zones prospectées par les pêcheurs. Les particularités biologiques de ce type de pêche sont analysées : les captures sont en général plurispécifiques; albacores (Thunnus albacares), listaos (Katsuwonus pelamis) et patudos (Parathunnus obesus) sont pêchés en proportions voisines avec des individus de tailles relativement petites en comparaison des zones voisines. Des hypothèses sont développées sur les causes et sur la dynamique de l'agrégation des thons autour de ces hauts-fonds en utilisant les statistiques de pêche journalières et les résultats de marquages classiques et par marques émettrices réalisés sur un mont sous-marin. Les perspectives de recherches sur l'association sous-marins et thons et sur l'exploitation rationnelle de ces micro-structures sont discutées. Les positions et les profondeurs des monts sous-marins étant actuellement facilement repérées grâce aux satellites à radar altimétrique, la localisation systématique de ces structures est possible et revêt pour les pêcheurs un intérêt potentiel évident pour réduire les temps de prospections des thoniers.

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.

The results of preliminary experiments in the development of a hatchery brood stock of whitefish of Lake Geneva, Coregonus shinzi palea Cuv. and Val. (lavaretus), are described. Factors likely to influence the date of spawning and the quality of eggs were studied by reference to the performance of wild spawners from the Lake Geneva. Fish were reared in tanks and the ovulation of females occurred spontaneously at the same spawning time as in wild spawners from the lake. Reared females have produced 30 000 eggs/kg against 45 000 in wild fish. The survival rate of a domestic egg was about 10% less than that of wild females. Since the overripening of the ova was rapid it was necessary to check the ripe females twice a week. The exposure of fish to long days in autumn delayed spawning by two months and permitted the synchronization of hatching under optimal conditions of growth. The ovulations were spread over a period of 3 months when the fish were subjected to long days until spawning. In contrast, termination of the long day regime in December induced a synchronization of the ovulations over just one month.

This paper presents a summary of information on reproduction biology in the scallop, Pectenmaximus, which is required for the successful reseeding and intensive aquaculture programs developed in France since 1982. Data are presented on the following subjects: environmental factors that sustain gametogenic activity and the time of year this activity occurs; biochemical changes that are associated with gametogenesis; the consistency of egg quality; and development of a simple test to predict egg quality.

The purpose of this study was to adapt the ethoxyresorufin O-deethylase (EROD) assay to the microplate technique. In addition to showing the practical advantages related to the intrinsic properties of such systems, we wished to demonstrate their potential value for biological monitoring of contamination in natural environments. A simpliffed procedure was developed for the preparation and fluorimetric assay of EROD activity using only basic laboratory equipment. The use of plate readers allows measurements to be done rapidly and provides numerous advantages in comparison with traditional methods. Within the context of our study; this test could be substituted to advantage for the enzymelinked immunosorbent assay (ELISA).