High-lipid diets are attributed to excessive lipid deposition and metabolic disturbances in fish. The aim of this experiment was to investigate the effects of steroidal saponins on growth performance, immune molecules and metabolism of glucose and lipids in hybrid groupers (initial weight 22.71 ± 0.12 g) fed high-lipid diets. steroidal saponins (0%, 0.1% and 0.2%) were added to the basal diet (crude lipid, 14%) to produce three experimental diets, designated S0, S0.1 and S0.2, respectively. After an 8-week feeding trial, no significant differences were found between the S0 and S0.1 groups in percent weight gain, specific growth rate, feed conversion ratio, protein efficiency ratio and protein deposition rate (p > 0.05). All those in the S0.2 group were significantly decreased (p < 0.05). Compared to the S0 group, fish in the S0.1 group had lower contents of serum triglyceride and low-density lipoprotein cholesterol and higher high-density lipoprotein cholesterol and glucose (p < 0.05). The activities of superoxide dismutase, catalase and glutathione peroxidase were significantly higher, and malondialdehyde contents were significantly lower in the S0.1 group than in the S0 group (p < 0.05). Hepatic triglyceride, total cholesterol and glycogen were significantly lower in the S0.1 group than in the S0 group (p < 0.05). Activities of lipoprotein lipase, total lipase, glucokinase and pyruvate kinase, and gene expression of lipoprotein lipase, triglyceride lipase and glucokinase, were significantly higher in the S0.1 group than in the S0 group. Interleukin-10 mRNA expression in the S0.1 group was significantly higher than that in the S0 group, while the expression of interleukin-6 and tumor necrosis factor-α genes were significantly lower than those in the S0 group. In summary, adding 0.1% steroidal saponins to a high-lipid diet not only promoted lipolysis in fish livers, but also activated glycolysis pathways, thus enhancing the utilization of the dietary energy of the groupers, as well as supporting the fish’s nonspecial immune-defense mechanism.

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An 8 weeks feeding trial was conducted in leopard coral grouper to observe the effects of dietary arginine (Arg) level on growth and skin health about development, pigmentation, antioxidant ability, immune capacity. Fish were feed five iso-lipidic and iso-proteic diets containing the Arg 2.4%, 2.9%, 3.4%, 3.9%, 4.4%, respectively. Results shown that the optimal dietary Arg value for best growth of leopard coral grouper was 3.72% of dry matter (corresponding to 6.73% of dietary protein) based on weight gain rate. The epidermis thickness of back skin and abdomen skin in Arg3.4, Arg3.9 and Arg4.4 groups was significantly higher than Arg2.4 and Arg2.9 groups. The SOD, carotene and astaxanthin in Arg4.4 group were significantly higher than Arg2.4 and 2.9 groups. Key genes in nicotinate and nicotinamide metabolism, gluconeogenesis, pentose phosphate, glutathione synthesis and ceramide synthesis pathways were significantly upregulated in Arg3.4 than Arg2.4 group, the synthesis genes of immune factors were significantly upregulated in Arg3.4 than Arg2.4 group. Suitable dietary Arg level can promote the morphological development, improve the antioxidant ability, enhance the immune capacity and reduce the consumption of pigment of skin. The results supported that Arg is an effective skin health enhancer for leopard coral grouper.