Dietary arginine requirement of juvenile yellow grouper Epinephelus awoara

An 8-week feeding trial was conducted to determine the dietary arginine requirement of juvenile yellow grouper Epinephelus awoara. Six isonitrogenous and isolipidic diets (43% crude protein and 10% lipid) were formulated to contain six graded dietary arginine levels ranging from 2.01 to 3.27% (dry weight) in about 0.3% increments. In all diets, amino acid nitrogen contents were kept the same by replacing arginine with a non-essential amino acid mixture. Each diet was randomly assigned to triplicated groups of 20 juvenile fish (about 4.23 g) twice daily to apparent satiation. The results indicated that the specific growth rate and weight gain at different dietary arginine levels were all significantly different. Maximal weight gain and specific growth rate occurred at 2.83% dietary arginine, however, weight gain and specific growth rate did not significantly increase with further increase in dietary arginine from 2.83% to 3.27%. Feed efficiency and protein efficiency ratio were not significantly affected by the dietary arginine levels. No mortality was observed at any diets. The dietary arginine levels significantly affected condition factor and hepatosomatic index, however, viscerosomatic index and muscle ratio were not significantly influenced by the dietary arginine levels. Crude protein, crude lipid and ash content in the muscle and dry matter in the whole body were significantly affected by the dietary arginine levels; fish fed with the 2.83% arginine diet had a higher crude protein content than fish fed with the other diets. There were no significant differences in red blood cell count, hemoglobin content and hematocrit among all treatments. Total nitric oxide synthase, inducible nitric oxide synthase in liver, and total nitric oxide synthase in plasma were significantly influenced by the dietary arginine levels. The essential amino acid concentrations in the muscle were significantly affected by the dietary arginine levels; however, there was no significant difference in essential amino acid concentrations in the liver. Quadratic regression analysis on specific growth rate and weight gain against dietary arginine levels indicated that the optimal dietary arginine requirement was estimated to be 2.8% of the diet (corresponding to 6.5% of dietary protein on a dry weight basis). (C) 2012 Elsevier B.V. All rights reserved.