By-catch of 0-group flounder, Platichthys flesus L. 1758, in the Loire glass-eel fishery was estimated for 1987 and 1988. Samples were taken throughout the estuary but the by-catch mainly occurred in the Central area. This pattern was observed in both surveys despite different hydrological conditions. The overall by-catch was 41 million animals for 1987 and 7 million for 1988. This difference was not only a consequence of a lowered fishing effort, it also suggests a difference in year-class strength. Recause of the great variability of postlarval distribution the accuracy of the estimates was very poor and only orders of magnitude can be discussed.

The general characteristics of the main salmon (Salmo salar L.) stocks in the Massif armoricain (Brittany and Lower Normandy), in the Loire-Allier and in the Adour-Gaves-Nive have been summarized. Due to the poor quality of the previous fishing statistics, there is no clear picture of the historical evolution of the salmon stock. However, a dramatic decrease in the endemic range of Atlantic salmon in France can be shown since the mid-18th century and more particularly during the last 50 years. The lack of precise informations describing the size of the catches and the levels of exploitation at sea and in the estuaries make it impossible to estimate the impact that exploitation has led on the evolution of salmon stocks. The mean age of salmon in freshwater ranges from 1 to 1.5 years. The Loire-Allier basin is characterized by a relatively high proportion of large salmon (3 fish) in the rod catches. Fish native to Brittany and Lower-Normandy (Massif armoricain) have lover growth rates than those from the Loire-Allier and Adour-Gaves-Nice Basins. A greater proportion of the early grilse stocks (migration May-July) are males than compared with fish running later. The sex ratio of the multi-sea-winter salmon is biased towards females.

The availability of various dietary carbohydrate sources for juvenile giant freshwater prawn, Macrobrachium rosenbergii, was evaluated according to weight gain and body composition. Different carbohydrate sources, α-potato starch, soluble starch, dextrin, sucrose, glucose and glycogen were separately included in a purified diet. After 60 days the greatest weight gain was achieved in the groups fed potato starch or soluble starch. The group receiving glucose as the carbohydrate source had low weight gain. Food conversion efficiency and the protein efficiency ratio were higher in the group receiving soluble starch as the dietary carbohydrate source. Muscle lipid consisted mainly of phospholipids and partial glycerides; midgut gland lipids were composed of triglycerides and phospholipids. A change in dietary carbohydrates had a minor influence on muscle lipid levels but caused variations in lipid class composition of the midgut gland. Comparatively high levels of free fatty acids and phospholipids were found in the midgut gland of groups fed soluble starch and potato starch, respectively. No major differences in fatty acid compositions were apparent. Soluble starch and potato starch were efliciently utilized by the prawn as dietary carbohydrate sources.

Tetraploidy was induced in embryos of Ruditapes philippinarum by treating the eggs with cytochalasin B (CB). Two treatment times were found to be effective in inducing tetraploidy: 0 to 10 minutes after insemination (before formation of the first polar body) and 45 minutes after insemination (just before the first cleavage). Treatments, started 5 and 45 minutes after insemination, produced $64.4\pm7.8{\%}$ and $28.3\pm2.3{\%}$ tetraploid embryos, respectively, after 6 hours (on the average over 3 experiments). However, no tetraploids were detected in 4-month-old spat. Sperm entry delayed by the CB could be involved in induction of tetraploidy by early treatment.

Entre marzo de 1986 y junio de 1987 se estudió et contenido de hierro, zinc y manganeso en partes duras y hierro, cobre, zinc y mercurio en gónadas del erizo de mar Echinometra lucunter, collectado en sitios del litoral rocoso habanero son diferente grado de contaminación metálica. Se obtuvieron variaciones estacionales y los resultados procesados mediante el análisis de varianza y el de clasificación automática, mostraron diferencias entre los sitios estudiados, que permiten considerar a este organismo como capaz de reflejar la contaminación por hierro y mercurio en sus gónadas y por los tres meules estudiados en sus partes duras.

Shell malformations and histological effects of environmental concentrations of TBTF (2, 13.1 and 64.8 ng/l) were assessed on adult oysters Crassostrea gigas during a 1-month experiment, including both an exposure and a depuration phase. The results showed that the digestive gland is the primary target organ. Recoverable modifications were observed at the lowest concentration. Limited necrosis was observed at the highest concentration and a longer exposure could have led to extensive and irreversible tissue lesions. Shell malformations (chambering) were observed during the depuration phase. Finally the authors suggest that safe TBT levels in mariculture waters should be lower than 2 ng/1.

About 60 papers and reports dealing with heavy metal contents in different eel species were reviewed in order to document various patterns of uptake, elimination and accumulation of these metals and to underline their detrimental effects (lethality, histo-pathology). Two main toxicological topics were considered: observations on contaminant levels in eels taken from the wild, mainly from contamined waters, and experimental studies under laboratory conditions.