Effects of dietary protein/energy ratio and water temperature on growth performance, digestive enzymes activity and non-specific immune response of spotted seabass (Lateolabrax maculatus)

This study investigated the effects of dietary protein/energy (P/E) ratio and water temperature on growth performance, blood biochemistry, digestive enzymes activity and innate immunity of spotted seabass (Lateolabrax maculatus). Six diets were formulated to contain two protein (440 and 470 g/kg) and three lipid levels (80, 110 and 140 g/kg) with P/E ratios of 22.31, 23.27, 23.47, 24.05, 24.35 and 25.55 g/MJ. Each diet was fed to two different sets of fish (2.67 +/- 0.01 g) kept at low temperature (27 degrees C; LT) or high temperature (33 degrees C; HT). Triplicate groups of fish were fed to apparent satiation three times daily for 8 weeks. The highest weight gain values were obtained at P/E ratios of 24.35 (470 g/kg protein and 110 g/kg lipid) and 23.47 (470 g/kg protein and 140 g/kg lipid) at LT and HT, respectively. Feed conversion ratio (FCR) was also significantly influenced by dietary P/E ratios where the lowest FCR was found in fish received the diet with P/E of 22.31 and kept at LT. Intestinal protease, amylase and lipase activities were neither affected by dietary P/E ratios nor water temperature. Significantly higher hepatic citrate synthase and succinate dehydrogenase activities were detected in LT groups. All serum innate immune parameters including lysozyme, complements 3 and 4, immunoglobulin and alkaline phosphatase were decreased by increasing water temperature. The findings in this study showed that optimal P/E ratios for spotted seabass at 27 and 33 degrees C are 22.31 and 23.47 g/MJ, respectively, and that high temperature induces retarded growth and suppressed immune function.