Effects of dietary lysine levels on growth performance and antioxidative capacity in channel catfish Ictalurus punctatus

A feeding trial was performed to investigate the effects of dietary lysine levels on growth performance and antioxidative capacity of channel catfish Ictalurus punctatus. Five isonitrogenous and isoenergetic diets with 19.3 (the control), 20.5, 22.1, 23.1 and 24.4 g kg(-1) of lysine were formulated. Results showed that compared with the control, 23.1 g kg(-1) dietary lysine increased the weight gain rate (WGR) and specific growth rate (SGR), and decreased the feed conversion ratio (FCR; p < 0.05). Based on the quadratic regression analysis of SGR and FCR, the optimal dietary lysine level was 22.2 and 21.9 g kg(-1), respectively. As dietary lysine levels increasing from 19.3 to 24.4 g kg(-1), the catalase activity increased significantly, while the malondialdehyde content decreased (p < 0.05). The mRNA levels of antioxidative genes in liver were markedly upregulated with the increase of lysine levels (p < 0.05). Meanwhile, the mRNA levels of target of rapamycin (TOR), kelch-like ECH-associated protein 1 (Keap1) and nuclear factor erythroid 2-related factor 2 (Nrf2) were increased (p < 0.05). In conclusion, 22.2 and 21.9 g kg(-1) dietary lysine could improve the growth performance of channel catfish. Besides, 24.4 g kg(-1) dietary lysine enhanced antioxidative capacity via the TOR/Keap1/Nrf2 signalling pathway.