Effect of dietary starch level on growth, metabolism enzyme and oxidative status of juvenile largemouth bass, Micropterus salmoides

A 60-day feeding trial was conducted to investigate the effect of dietary carbohydrate level on the growth performance, body composition,plasma biochemical indices and antioxidant capacity of largemouth bass, Micropterus salmoides. Six isonitrogenous and isolipidic diets containing graded levels of starch (0%, 5%, 10%, 15%, 20% and 25%) were fed to juvenile largemouth bass. The weight gain (WG), specific growth rate (SGR) and protein efficiency ratio (PER) decreased with increasing dietary starch levels (P < .05), whereas feed conversion ratio (FCR) showed the opposite trend. Feed intake (FI) was found to be not significantly related to the dietary starch levels (P < .05). However, liver lipid, hepatic glycogen and muscle glycogen contents increased significantly with dietary starch levels. There were significant differences in hepatic glucose metabolism enzymes in fish fed diets with different dietary starch levels. The hexokinase (HK), glucokinase (GK), and pyruvate kinase (PK) activities in liver increased significantly as dietary starch levels increased, whereas fructose-1,6-bisphosphatase (FBPase), phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) activities in liver showed the opposite trend. Moreover, the superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and inducible nitric oxide synthase (iNOS) activities, nitric oxide (NO) concent in liver decreased significantly as dietary starch levels increased, while the malondialdehyde (MDA) contents in liver increased. Results demonstrate that the starch levels may affect growth performance and metabolic changes in hepatic intermediary metabolism, which suggest that starch diets were inefficiently used as an energy source by M.salmoides juveniles.