Dietary arginine requirement of juvenile red sea bream Pagrus major

•Fish growth was significantly improved by increment of arginine up to 2.54%.•Whole-body and muscle compositions were significantly influenced by arginine levels.•Dietary arginine increment affected fish hematology and enhanced innate immunity.•Serum T-NOS activity was significantly increased at 3.08% arginine level.•Arginine requirement was estimated at 2.37% of diet for juvenile red sea bream.

A 9-week feeding trial was carried out to evaluate dietary arginine requirement of juvenile red sea bream. Six isonitrogenous and isocaloric diets (50% crude protein and 17.7 kJ g− 1 gross energy) were formulated to contain graded levels of arginine including 1.42, 1.88, 2.22, 2.54, 3.08 and 3.43% of diet (2.84–6.86% of dietary protein), and fed triplicate groups of fish (13.3 ± 0.2 g) to apparent satiation twice daily. At the end of the feeding trial, fish fed ≥ 2.22% arginine showed significantly (P < 0.05) higher growth than those fed 1.42% arginine. Significant improvement in protein productive value was found at dietary arginine level of 2.54% compared to the fish fed 1.42% arginine. Significant reductions in whole-body and muscle lipid contents were found by increment of arginine level and whole-body protein increased significantly in fish fed 2.22–2.54% arginine compared to those fed 1.42% arginine. Plasma total protein level significantly was increased in fish fed 2.54–3.08% arginine, and alanine aminotransferase activity and glucose level were significantly decreased in fish fed 2.22–2.54% and ≥ 1.88% arginine, respectively, compared to the group fed 1.42% arginine. Significant improvements in lysozyme and myeloperoxidase activities and total immunoglobulin level were obtained by dietary arginine increment. Also, significantly higher total nitric oxide synthase activity was recorded at 3.08% arginine level in comparison to 1.42% arginine. A broken-line regression analysis on weight gain showed that the optimum dietary arginine level is 2.37% of diet (4.74% of dietary protein).