Effect of dietary lipid levels on the anti-oxidant responses, initial immunity, and mTOR signaling in the liver of coho salmon (Oncorhynchus kisutch)

In the present study, we evaluated the effects of dietary lipid levels on the anti-oxidant responses, initial immunity, and mTOR signaling in the liver of coho salmon Oncorhynchus kisutch. The post-larval coho salmon were fed four isonitrogenous experimental diets with crude lipid levels of 6.6%, 10.56%, 18.91%, and 26.91% for 12 weeks, respectively. Compared to the control group (6.6% dietary lipid level), the activities of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), peroxidase (POD), glutathione peroxidase (GSH-PX), and total antioxidant capacity (TAC) were enhanced by 10.56% and 18.91% dietary lipid levels in the liver of coho salmon. However, no significant difference was observed on these anti-oxidant enzyme activities when the fish were fed 26.91% lipid level diet. Compared to the control group (6.6% dietary lipid level), the content of hydrogen peroxide (H2O2) and malondialdehyde (MDA) as well as the generation of hydroxy radical (.OH) and superoxide anion (O-2(center dot-)) were decreased by 10.56% and 18.91% dietary lipid levels. In addition, the gene and protein expression level of PI3K, Akt, and mTOR was induced by 10.56%, 18.91%, and 26.91% dietary lipid levels. The gene expression level of IL-1 beta, IL-6, and TNF alpha was also increased with the increase of dietary lipid levels. The result of hepatic tissue sections showed that the cellular morphology of liver was affected by the higher dietary lipid levels. In conclusion, the dietary lipid levels affected the anti-oxidant responses, initial immunity, and mTOR signaling in the liver of post-larval coho salmon.