A 110-day feeding trial was conducted to determine the effects of dietary arginine levels on growth performance, amino acid metabolism, immune response, and disease resistance of abalone Haliotis discus hannai (initial weight: 15.70 +/- 0.03 g). Seven isonitrogenous (about 32% of crude protein) and isolipidic (about 3% of crude lipid) diets with 1.17% (the control), 1.36%, 1.68%, 2.19%, 2.47%, 2.82% and 3.43% of arginine were formulated. Each diet was randomly assigned to triplicate cages (5 layers, each layer was 40 cm x 35 cm x 14 cm) with 80 abalones per cage. At the end of the feeding trial, abalones were fasted for 72 h and anesthetized with 5% alcohol. Results showed that final body weight and biomass gain (BG) increased first and thereafter decreased, where the breakpoints (34.11 g and 934.41 g, respectively) were found in the 1.68% dietary arginine group. Based on the brokenline regression analysis of BG, the optimal dietary arginine level for abalone was estimated to be 1.64% of dry diet. Abalone fed with 2.47% of dietary arginine showed higher crude protein content in the soft body (17.59% wet weight) than other groups. The crude lipid content had a decreasing trend (from 2.02 to 1.28% wet weight) with increasing dietary arginine. The concentration of total free essential amino acids in hemolymph was significantly higher in 1.68% (207.30 mu g/mL), 2.19% (199.17 mu g/mL) and 2.47% (216.30 mu g/mL) dietary arginine groups than that in the control group (P < 0.05). Activities of alanine aminotransferase, total nitric oxide synthase, total anti-oxidative capacity, lysozyme, and the contents of nitric oxide, total protein and albumin were significantly increased as dietary arginine levels increasing from 1.17% to 1.68% and then decreased (P < 0.05). In the digestive gland, the genes expression of nuclear factor erythroid 2-related factor 2, catalase, glutathione peroxidase and Cu/Zn superoxide dismutase were significantly increased in 1.68% dietary arginine group compared with that in the control group (P < 0.05), while the gene expression of kelch-like ECH-associated protein 1 showed an opposite trend. Meanwhile, the gene expression of tumor necrosis factor-alpha was decreased in 1.36% to 2.82% dietary arginine levels, and the gene expression of Arginase-I was increased in the 1.68% dietary arginine group. The cumulative mortality of abalone challenged with Vibrio parahaemolyticus (1.0 x 107 cfu/mL) for seven days was significantly decreased in the 1.68% dietary arginine group (36.67%) compared with those in the other groups except for the group with 2.19% of dietary arginine. In conclusion, dietary arginine level (1.68%) improved the growth, anti-oxidative capacity, immunity and disease resistance of abalone.
