Annie Pastoureaud

Quantitative methionine requirement of juvenile sea-bass (Dicentrarchus labrax)

Abstract The methionine (MET) requirement of sea-bass was studied by the nutrient-response relationship using growth rate data and free MET levels in serum and whole blood after feeding. Two series of diets were employed, sharing a common basal diet. This basal diet contained a mixture of soybean, yeast and fish meals as protein source, and was formulated to be deficient in MET whereas the other essential amino acids levels corresponded to the pattern found in sea-bass muscle proteins. Graded levels of MET were obtained by supplementing the basal diet with crystalline MET (S series) or by substituting soybean and yeast meals by fish meal (F series). Fish were fed for 85 days on an optimal ration (1.5%/day). The MET requirement could be determined only with the F series diets using sigmoidal mathematical models. Inflexion points from curves obtained with the data for weight gain and for free MET in the blood were very similar. The MET requirement was estimated at about 1% of dry diet or 2% of dietary protein or 15 mg/day per 100 g live weight. The S series diets allowed us to determine, from growth data, the optimal level of MET supplementation: optimal growth rate occurred with 1.3% total MET content in the diet, with 0.6% in the crystalline form. Further supplementation depressed growth rate. Choices of types of diet, advantages of the biochemical method and use of sigmoidal models for computer fitting of experimental data are discussed.

Influence de la temperature et de la salinite sur la croissance et la composition corporelle d'alevins de Dicentrarchus labrax

Abstract Growth, food conversion, and body composition of sea bass fingerlings, Dicentrarchus labrax , exposed to different temperatures (15 and 22°C) and salinities (6, 11, 24 and 37‰) were studied. Temperature was found to have the more significant influence on these parameters. At the higher temperature, fingerlings grew faster in high and low salinities (6 and 37‰). At the lower temperature, growth was slightly faster at 11 and 24‰. Body composition was affected mainly by temperature; salinity had no significant effect. Trypsin-like activity in the digestive tract was very low at 6‰ and 15°C. Sea bass fingerlings seem to be very tolerant to changes in temperature and salinity of their environment. The results are discussed in the context of fish culture.

Influence of starvation at low temperatures on utilization of energy reserves, appetite recovery and growth character in sea bass, Dicentrarchus labrax

Abstract The effect of starvation at selected low temperatures was studied in sea bass,Dicentrarchus labrax. The work focused on proximate chemical constituents and blood glucose. Appetite and growth of starved, refed specimens were also examined. Two experimental sets were designed. In one set the fish were exposed to 3 °C, 7 °C and 11 °C and in the other to 3 °C, 8 °C and 13 °C. Survival of the fish in the experimental conditions was 99.7%. Appreciable loss in body weight occurred. The reduction was more marked in the first week. No significant difference in chemical composition occurred in the first two weeks of starvation. Prolongation of food deprivation resulted in decline of lipid content with a corresponding increase in water content. This trend was the more marked at high temperature. Liver glycogen was the most readily utilizable source of energy. Lipid yielded energy after which proteins were mobilized to save further loss of lipid. Lipid exerted a sparing role for glycogen. The preference for different energy sources depended on exposure temperature and duration of starvation, Lipid chiefly supplied the energy needs of the 3 °C test groups, whereas liver glycogen provided the calorific requirements of fish at 7 °C, 8 °C, 11 °C and 13 °C. In the 3 °C test groups gluconeogenesis occurred after 2 weeks. The products of lipid breakdown may have served as substrates for glycogen biosynthesis. High tolerance of sea bass to low temperature was attributed to high fat content and hyperglycemia. The study also pointed to the involvement of some organs other than liver in generating glucose from their glycogen stores following exhaustion of hepatic glycogen. Starvation stress at the lowest temperatures adversely affected the return of the fishs appetite and growth characters. Compensatory growth occurred in sea bass refed after starvation. The findings have implications for aquaculture management procedures.

Red coloration of oysters along the French Atlantic coast during the 1998 winter season: implication of nanoplanktonic cryptophytes

During a 4-week experiment on oyster grazing in coastal ponds (claires) near La Rochelle (France), a red coloration was observed in the digestive gland of oysters. This pigmentation was attributed to an intensive grazing on cryptophyte nanoflagellates. Three different techniques led to this conclusion, mentioning for the first time free-living cryptophytes as responsible for such a phenomenon. Spectrofluorometry was used to demonstrate that the red coloration was due to the presence of a phycoerythrin, characteristic of cryptophytes. Microscopic observations and accessory pigments analyses in water ponds confirmed that the source of this pigment was of cryptomonadal origin. Oyster grazing on these algae is evidenced by large differences in alloxanthin concentrations and flagellate abundances between the two experimental ponds. The winter occurrence of this phenomenon is of importance for oyster commercialization and a short-term depuration is suggested to remove the undesirable pigmentation.