Addition of L-carnitine to formulated feed improved growth performance, antioxidant status and lipid metabolism of juvenile largemouth bass, Micropterus salmoides

L-carnitine is essential for fatty acids transportation from cytosol into the mitochondrial matrix, and promotes the beta-oxidation of long-chain fatty acids to provide energy for fish. The aim of this study was to research the effect of dietary L-carnitine on the growth performance, antioxidant capacity and lipid metabolism in juvenile largemouth bass, Micropterus salmoides. Four formulated diets (Diet 1, Diet 2, Diet 3 and Diet 4) were supplemented with graded levels (0, 0.1, 0.2 and 0.3 g/kg) of L-carnitine. The results showed dietary supplementation of 0.1 g/kg L-carnitine significantly increased weight gain, while 0.3 g/kg L-carnitine supplementation decreased viscerasomatic index and intraperitoneal ratio of largemouth bass. The Plasma high density lipoprotein cholesterol (HDL-C) content of the fish which fed Diet 2 and Diet 4 were significantly higher than the fish fed Diet 1. Fish fed Diet 1 had significantly lower hepatic glutathione peroxidase (GSH-Px) activity and mRNA expression than fish fed Diet 2, Diet 3 and Diet 4. Contrary, fish fed Diet 1 had significantly higher hepatic fatty acid synthetase (FAS) activity and the mRNA expression than fish fed Diet 2, Diet 3 and Diet 4. Fish fed Diet 2, Diet 3 and Diet 4 had significantly increased the activity of hepatic carnitine palmitoyltransferase (CPT1), but no significant effect on the expression of hepatic CPT1 gene than fish fed Diet 1. In conclusion, these results confirmed that dietary supplemented of L-carnitine was beneficial for promoting growth in largemouth bass and could improve the antioxidant capacity. Furthermore, L-carnitine could play an important role in fatty acids metabolism.