Effects of dietary lysine on regulating GH-IGF system, intermediate metabolism and immune response in largemouth bass (Micropterus salmoides)

Carnivorous fish have a high requirement for lysine to get optimal growth and health status. However, the mechanisms of lysine in regulating growth, intermediate metabolism and immune response have not been fully revealed in fish species. In this experiment, largemouth bass ( Micropterus salmoides ), a popular carnivorous fish, was chosen to explore the molecular response after the fish fed with lysine control diet (LC diet), low lysine diet (LL diet) and lysine supplementation diet (LS diet) for 8 weeks, respectively. Results showed that compared with the LC diet, the LL diet led to a reduction of plasma nutrients concentration and hypoactivated growth hormone-insulin like growth factor (GH-IGF) signaling pathway which further impaired lipogenesis and lipolysis. Lysine supplementation to the LL diet had effective effects on alleviating the repression of GH-IGF pathway and nutrient anabolism. Furthermore, the LL diet significantly activated kidney pro-inflammatory and anti-inflammatory responses. Lysine supplementation significantly suppressed these effects to the control level. The present study demonstrated that dietary lysine levels led to distinct GH-IGF response, which in turn regulated the lipid me-tabolism, pro-inflammatory and anti-inflammatory response. Our results provide a molecular basis for using lysine to improve nutrients metabolism and immune response in fish species.