Effects of dietary arginine levels on growth, immune function of physical barriers and serum parameters of spotted seabass (Lateolabrax maculatus) reared at different water temperatures

Abstract

A growth experiment was conducted to investigate the effects of dietary arginine levels on growth, immune function of physical barriers and serum parameters of spotted seabass (Lateolabrax maculatus) reared at different water temperatures (27°C and 33°C). Six iso‑nitrogenous and iso‑lipid diets were formulated with 1.16%, 1.65%, 2.04%, 2.44%, 2.98% and 3.36% arginine, respectively. Growth of fish reared at 27°C was significantly higher than that of fish reared at 33°C (P < 0.05). Weight gain (WG) increased first and then decreased with the increase of arginine levels, and the maximum value was obtained in fish fed the diet with 2.04% arginine at 27°C or 33°C. As for immune function of physical barriers, activities of antioxidant enzymes (GPx and SOD) and expression of genes related to tight junction (ZO-1, Occludin and Claudin b) were significantly higher in the gills of fish reared at 27°C than those of fish reared at 33°C (P < 0.05). Furthermore, activities of GPx and SOD and the mRNA expression of ZO-1, Occludin and Claudin b reached the maximum values in the gills of fish fed the diet with 2.44% or 2.04% arginine at 27°C among all treatments. The mRNA expression of MAPK p38 and MyD88 and contents of pro-inflammatory cytokines (IL-1β, IL-6 and TNFα) were significantly lower in the intestine of fish reared at 27°C than those of fish reared at 33°C (P < 0.05). Regardless of water temperature, contents of IL-1β, IL-6 and TNFα as well as the mRNA expression of MAPK p38 and MyD88 reached the minimum values in the intestine of fish fed the diet with 2.04% or 2.44% arginine at 27°C among all treatments. As for serum parameters, the activity of iNOS as well as contents of NO, complements 3 and 4 were significantly higher in fish reared at 27°C than those of fish reared at 33°C (P < 0.05). Regardless of water temperature, serum activities of TNOS and iNOS reached the maximum values in fish fed the diet with 2.04% or 2.44% arginine among different arginine supplementation groups. The activity of lysozyme reached the maximum value in fish fed the diet with 2.04% arginine level at 27°C among all treatments. Those results showed that a water temperature of 33°C decreased growth, immune function of physical barriers and serum parameters of fish. Growth and immunity were maximized when the arginine requirement of spotted seabass was met. Second-order polynomial regression analyses of WG and lysozyme activity showed that the arginine requirement of spotted seabass was 2.47% and 2.53% of the dry diet (5.49% and 5.62% of dietary protein) at 27°C as well as 2.40% and 2.37% of the dry diet (5.33% and 5.27% of dietary protein) at 33°C, respectively.