Dietary arginine requirement and effects of dietary arginine levels on the metabolism of Scophthalmus maximus

The purpose of this study was to investigate the arginine requirement and effects of dietary arginine levels on the growth and metabolism of turbot (Scophthalmus maximus). Turbots with an initial body weight of (43.07±0.10) g were selected as the research object. Five isonitrogenous and isolipid diets (51% crude protein and 12.5% crude lipid) were formulated with casein and gelatin as the main protein sources and fish oil and soybean lecithin as the lipid sources. The arginine contents of the diets were 1.92%, 2.65%, 3.40%, 4.17% and 4.88% of dry matter by adding crystalline amino acid mixture, respectively. (The corresponding diet number was 1, 2, 3, 4 and 5, respectively). The group fed 1.92% arginine level diet served as control group. Each treatment was set to 3 replicates, each containing 12 fish, and the breeding period was 10 weeks. The results showed that 3.40% to 4.88% arginine (6.66% to 9.52% of dietary protein) significantly improved the growth performance and feed utilization of turbot compared with the control group. According to the broken line regression analysis based on specific growth rate (SGR), the optimal dietary arginine requirement of turbot was estimated to be 3.17% of dry matter (6.21% of dietary protein). Appropriate dietary arginine levels significantly increased body protein content and plasma total protein level, while significantly decreased plasma glucose level. In addition, appropriate dietary arginine levels significantly enhanced the expression of genes related to fatty acid synthesis, fatty acid β-oxidation, glycolysis, tricarboxylic acid (TCA) cycle and oxidative phosphorylation, while significantly decreased the expression of genes associated with amino acid degradation in liver. The results demonstrated that 3.40% to 4.88% arginine (6.66% to 9.52% of dietary protein) can regulate the nutrient metabolism and promote the growth of turbot.