Effect of dietary lipid level on growth, lipid metabolism and oxidative status of largemouth bass, Micropterus salmoides

This study was conducted to evaluate the effect of dietary lipid levels on growth, body composition and liver oxidative stress of largemouth bass, Micropterus salmoides. Fish were fed isonitrogenous (crude protein 45%) practical diets with five lipid levels (3.3%，8.2%，13.2%，18.1% and 23.3%, respectively) for 60 days. The results showed that weight gain (WG) and protein efficiency ratio (PER) were all significantly improved by dietary lipid levels up to 18.1% and then levelled off beyond this level. Both feed intake (FI) and feed conversion ratio (FCR) showed a decreasing trend with dietary lipid increased. Body lipid content, liver lipid content, total n-3 and n-6 PUFA content in muscle, and triglyceride (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) contents in plasma significantly increased with increasing dietary lipid levels. However, body protein content, and HDL-C/TC and HDL-C/LDL-C values significantly reduced. The carnitine palmitoyltransferase I (CPT-1), lipoprtein lipase (LPL), glucose-6-phosphatase (G6Pase), phosphoenolpyruvate carboxykinase (PEPCK) and fructose-1,6-bisphosphatase (FBPase) activities in liver increased significantly as dietary lipid levels increased, whereas both fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC) activities showed the opposite trend. Moreover, higher superoxide dismutase (SOD), catalase (CAT) and oxide synthase (NOS) activities, and nitric oxide (NO) concent in liver were recorded in fish fed diets with 18.1% lipid, while the malondialdehyde (MDA) content in liver increased as dietary lipid levels increased. Results indicated that high dietary lipid level (23.3%) inhibit weight gain and induce oxidative stress, which affect the health status of largemouth bass. Based on WG, a dietary lipid level of 18.42% was optimal for growth performance of juvenile largemouth bass.