Does dietary n−3 highly unsaturated fatty acids level influence the European sea bass ( Dicentrachus labrax) capacity to adapt to a high temperature?

Abstract

Triplicate groups of European sea bass juveniles (60 g) were fed for 84 days two experimental diets containing either vegetable or marine oil (0.4 and 2.2% n−3 highly unsaturated fatty acid [ n−3 HUFA] dry matter in LD and HD, respectively) and held at 22 or 29 °C (LD-22, LD-29, HD-22 and HD-29 groups). Significant differences in mass gain between the two diets and temperatures were observed from day 28 onwards, and on day 84, weight was 18% higher in the HD-29 group than in the LD-22 group (the highest and lowest values, respectively). Over the 84-day period, SGR was significantly affected both by temperatures and diets ( P=6×10 −4 and 2×10 −4 respectively), averaging 1.01 and 1.07 in the HD-22 and HD-29 groups compared to 0.92 and 1.0 in the LD-22 and LD-29 groups. Differences in growth rate between the experimental conditions were mainly explained by differences in feed intake (FI). FI was more affected by temperature than by diets (in fish fed HD, it was 1.7% day −1 at 29 °C and 1.4% day −1 at 22 °C, and 1.7% day −1 and 1.3% day −1, respectively, with LD). Feed conversion ratio (FCR) was significantly affected by temperature and diets; days 0–84 FCR was on HD and LD 1.6 and 1.7 at 29 °C and 1.4–1.5 at 22 °C. Considering growth and feeding parameters, no interaction between dietary concentration in n−3 HUFA and temperatures were observed. In acclimated fish, MO 2 on routine metabolism was the highest at HD-29 (396 mg O 2 kg −1 h −1) as it was dependent on FI. There was no major difference in fish whole body composition, and protein retention was more affected by temperature than by diets. Diets and temperature affected polar lipid fatty acid content, without interaction; n−3 HUFAs were lower at 29 °C than at 22 °C. Fatty acids of total and neutral lipids (NL) were mainly affected by dietary fatty acids, while some low but significant influences of temperature were observed. Interactions between the two studied factors concerned particularly n−3 HUFAs content, lower at 29 than at 22 °C only in fish fed vegetable oil (LD). This study demonstrated that in high-quality sea bass juveniles, a 3-month deficiency in dietary n−3 HUFA did not drastically impair fish capacity to adapt to a high temperature, 29 °C.