Associations between tissue fatty acid composition and physiological traits of performance and metabolism in the seabass (Dicentrarchus labrax).

Seabass were fed for 4 months with diets where the lipid was provided as either canola oil (CO), palm oil (PO) or fish oil (FO), to generate diversity in their tissue fatty acid (FA) composition and investigate how this influenced major traits of exercise performance, cardiac performance and respiratory metabolism. In particular, based upon previous observations, we investigated the hypothesis that enriching the fish tissues with oleic and linoleic acids (OA, 18:1n-9 and LA, 18:2n-6, respectively) from the CO and PO diets would improve maximum exercise and cardiac performance, and increase aerobic metabolic scope. This proved to be the case; exercise respirometry on bass fitted with cardiac flow probes revealed that those fed CO and PO diets had a significantly higher critical swimming speed (U(crit)) than those fed the FO diet. The improved swimming performance in the CO and PO groups was accompanied by a higher maximum cardiac output (Q) and net cardiac scope, and a higher active metabolic rate (AMR) and aerobic scope (AS) than in the FO group. Analysis of tissue FA composition revealed that the fish fed the CO and PO diets had accumulated significantly higher levels of OA and LA in their heart and muscle than the fish from the FO group, which had significantly higher levels of highly unsaturated FA of the n-3 series, such as EPA and DHA (20:5n-3 and 22:6n-3, respectively). Principal components analysis revealed significant positive associations between tissue OA and LA content and U(crit), maximum Q, the increase in Q during exercise, AMR and aerobic scope. There was a negative association between these physiological traits and tissue content of EPA. Therefore, diet composition is an environmental factor that can generate significant phenotypic diversity in major physiological traits of performance and metabolism in the seabass, with increased intake of FAs such as OA and LA leading to improved cardiorespiratory performance.

Carbohydrate production in relation to microphytobenthic biofilm development: an integrated approach in a tidal mesocosm.

Experiments were performed to evaluate short-term changes in sediment extracellular carbohydrates for a multispecific assemblage of benthic diatoms in relation to physiological status, endogenous migratory rhythms, and environmental conditions. For this purpose, a mesocosm was used, which simulated both tidal and dark: light alternating cycles under controlled conditions. Scanning electronic microscopy in combination with picture analyses indicated that natural diatom migration patterns were reproduced in the mesocosm. Two EPS fractions were operationally separated in colloidal carbohydrate measurements: alcohol-soluble EPS (termed "soluble EPS") and alcohol-insoluble EPS (termed "bound EPS"). Microphytobenthic biomass followed a logistic-type curve and converged toward a maximal value termed the "biotic capacity of the local environment." Both EPS fractions showed oscillations with production during photosynthetic periods and sharp decreases during night immersion periods. Productions of both EPS fractions increased with Chl a production during light periods suggesting a light dependence in relation to migratory patterns. The decreases in both EPS fractions, which occurred during night immersion periods suggest that carbohydrate hydrolysis and/or washaway affected both EPS fractions similarly in benthic environments. Our results confirm the theory according to which the two distinct fractions are under different metabolic controls. No change in soluble EPS release was obtained during the transition from logarithmic to stationary phase. On the other hand, a metabolism modification of microalgae, probably related to ammonium depletion, occurred when cells entered the stationary phase, since there was a high enhancement in bound EPS production. Mesocosm results can serve as a system of reference useful to characterize biofilm development in field investigations and to revisit the effective implication of each EPS fraction in sediment stability.

[Circadian variations in hemolymph lipids and lipoproteins and in hepatopancreatic lipids of the shrimp Penaeus japonicus]. / Variations circadiennes des lipides et lipoprotéines de l'hémolymphe, et des lipides de l'hépatopancréas, chez la crevette Penaeus japonicus.

Lipids content of the haemolymph and the hepatopancreas in the decapod Crustacean P. japonicus exhibits a bicircadian rhythm characterized by one maximum in the night and another one during the day. The maximal values in the haemolymph are approximately two and a half times greater (8 mg/ml) than minimal ones (3 mg/ml). Variations are less important in the hepatopancreas. A bicircadian rhythm of lipid classes in the haemolymph is observed very significantly in concentration of polar lipids and free sterols with maximal values (6.87 mg/ml and 0.59 mg/ml) and minimal values (2.63 mg/ml and 0.23 mg/ml) respectively. Polar lipids are the major lipid fractions in the haemolymph (87%). The electrophoretic behaviour of haemolymph lipoproteins is determined.