Effects of leucine on growth performance and liver glucolipid metabolism of Micropterus salmoides fed a high-carbohydrate diet

Carbohydrates (CHO) play an excellent role as both energy and carbon sources for animals. Therefore, it has been widely used in practical feed. However, unlike the case in mammals, it is generally acknowledged that carbohydrates cannot be fully and efficiently used by teleost fish. In fact, most fish species have been considered as “glucose intolerant”, and often display a prolonged postprandial hyperglycemia after glucose loading or the intake of carbohydrate-enriched diets. Until now, the underlying mechanisms are still poorly understood. Leucine, a chain amino acid, is an EAA required for the optimum growth of mammals and fish. Its supplementation could improve glucose tolerance and insulin sensitivity. However, the long-term effects of leucine on the growth performance and intermediary metabolism of fish fed a high-carbohydrate diet is still absent. In this study, a 12-week feeding trial was performed to fish (average body weight 5.35 ± 0.04 g) were randomly fed three diets, namely CON group (10% carbohydrate level), high-carbohydrate group (HC, 20% carbohydrate level), high carbohydrate + leu group (HCL, 20% carbohydrate level + 2.0% leucine). The results showed that fish fed the HC diet had a lower final fish weight, specific growth rate (SGR), weight gain rate (WGR), feed coefficient (FCR), as well as the expression of g6pase, pparα, cptIa and aco1 compared to those fed the CON diets, whereas plasma glucose, triglyceride (TG), advanced glycation end products (AGES) and glycosylated serum protein (GSP) levels, liver lipid content, as well as the expression of glut2, gk, pk, gs, srebp1, fas, acc1, chrebp and selp showed an opposite trend. FCR, the plasma glucose, AGES and GSP levels, liver lipid content, as well as the expression of foxo1, fbpase, and g6pase of HCL groups were significantly (P < 0.05) decrease compared to those of the HC groups, whereas the opposite was true for final fish weight, SGR and WGR, whole body lipid contents, as well as the expression of glut2, gk, pk, gs, srebp1, fas, acc1, chrebp, selp, pparα, cptIa and aco1. Overall, leucine could improve the growth performance and feed utilization of M. salmoides fed the high-carbohydrate diet through the stimulation of glycolysis, glycogenesis, lipogenesis and fatty acid oxidation coupled with the depression of gluconeogenesis. The data obtained here will facilitate our understanding of the underlying mechanisms by which leucine benefits the carbohydrate metabolism of fish.