Dietary oleic acid supplementation improves feed efficiency and modulates fatty acid profile and cell signaling pathway in European sea bass (Dicentrarchus labrax) juveniles fed high-lipid diets.

Diets with high-lipid levels may reduce fish growth, feed intake and increase fat deposition, jeopardizing fillet quality and shelf-life, which may be of major concern for the final consumer. To mitigate these potentially harmful effects, several nutritional strategies have been applied, including the use of functional ingredients. In this study, European sea bass (initial body weight 21.4 g) were fed six isonitrogenous (45% crude protein) diets with 16% and 22% lipid levels and supplemented with oleic acid (OA) at 0, 1, and 2% as a functional ingredient. Increasing dietary lipid levels did not affect fish growth performance, feed intake, and feed utilization. Independently of lipid level, dietary OA supplementation decreased feed intake and increased feed efficiency and Nitrogen (N) retention (% N Intake). Whole-body composition, hepatosomatic and visceral somatic indexes were not affected by dietary composition. The liver and muscle lipid contents were also not affected by dietary composition. The liver fatty acid profile was not affected by dietary lipid level, but monounsaturated fatty acid (MUFA) content decreased while polyunsaturated fatty acid (PUFA) content decreased with dietary OA supplementation. In the muscle, PUFA content decreased with dietary lipid levels, particularly C18:2n-6 (LA) and C20:2n-6. Dietary OA supplementation increased muscle MUFA, particularly OA (C18:1n-9), and reduced PUFA content. Compared to fish fed with 1OA diets, fish fed with 2OA diets presented a decreased area covered by lipids in the liver. Dietary OA supplementation increased hepatic glucose-6-phosphate dehydrogenase (G6PDH) activity and decreased malic enzyme (ME) activity, while no differences were observed in the activity of fatty acid synthase (FAS) and enzymes related to β-oxidation. Moreover, dietary OA supplementation decreased mechanistic target of rapamycin (mTOR) protein levels, while protein kinase B (Akt) and the phosphorylated state levels of both Akt and mTOR were not affected by dietary composition. Overall, dietary OA supplementation decreased feed intake and improved feed efficiency, without affecting growth performance, contributing to mitigate the potentially harmful effects of high-lipid diets in European sea bass. • Growth performance and feed utilization were not affected by dietary lipid levels. • OA supplementation decreases FI and improves FE and NR (% NI). • Dietary OA supplementation increased MUFA but decrease PUFA content in the liver. • Dietary OA supplementation decreased mTOR protein levels. [ABSTRACT FROM AUTHOR]