Effect of dietary L‐carnitine supplementation on growth performance and lipid metabolism in Rhynchocypris lagowski Dybowski fed oxidized fish oil

Lipid content of a diet is very susceptible to oxidation, which has many negative effects on farmed animals. Therefore, this study studied the protective effect of L‐carnitine (LC) on fish body stimulated by oxidized fish oil (OFO) from lipid metabolism. Lipid content of the diet was replaced by OFO in 0, 100 and 400 meq/kg. L‐carnitine was added to the diet in two levels, 500 and 1,000 mg/kg, giving a total of seven experimental diets. A total of 735 healthy Rhynchocypris lagowski Dybowski with an initial weight of 4.48 ± 0.14 g after 2‐week adaptation randomly divided into 15 glass aquariums. Fish were fed satiated three times daily. After 8 weeks, biometry was done to evaluate growth performance, and hepatopancreas and muscle samples were taken for biochemical analysis. The result showed that feeding with OFO had negative growth. However, in fish received both OFO and LC, growth indices improved slightly (p > .05). Feeding with OFO and LC, the content of EPA, DHA and PUFA in the muscle of R. lagowski was significantly higher than that in the control group (p < .05), which reached the maximum value in the OFO100 + LC500 group. The content of SFA, MUFA, ∑n‐6 and PUFA in hepatopancreas increased significantly (p < .05), and the content of SFA reached the maximum in OFO100 + LC500 group. Feeding with OFO increased hepatopancreas total cholesterol, triacylglycerol, HDL/LDL ratio, FAS and ACCα that involved in lipid synthesis enzymes, while reduced HL and HSLα enzyme activity and gene expression that associated with lipid decomposition. Dietary LC moderated the effects of OFO on lipid metabolism. According to the result of the present study, it can be argued that feeding of R. lagowski with OFO has negative effects on growth performance and lipid metabolism, whereas LC dosages used in this study have increased the oxidation rate of fatty acids in the hepatopancreas of R. lagowski and improved the accumulation of fat in hepatopancreas cells induced by oxidized fish oil.