Abstract
P>To quantify the optimum dietary arginine requirement of fingerling Indian major carp, Labeo rohita (4.10 +/- 0.04 cm; 0.62 +/- 0.02 g), an 8-week growth trial was conducted in eighteen 70-L indoor circular aqua-coloured troughs provided with a flow-through system at 28 +/- 1 degrees C. Isonitrogenous (40 g 100 g-1 crude protein) and isocaloric (4.28 kcal g-1 gross energy) amino acid test diets containing casein and gelatin as intact protein sources with graded levels of arginine (0.5, 0.75, 1.0, 1.25, 1.50 and 1.75 g 100 g-1 dry diet) were fed to triplicate groups of fish to apparent satiation at 07:00, 12:00 and 17:30 hours. Growth performance of fish fed the above diets was evaluated on the basis of absolute weight gain (AWG), specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency ratio (PER), protein retention efficiency (PRE) and energy retention efficiency (ERE). Maximum AWG (2.61), SGR (2.80), best FCR (1.35), highest PER (1.85), PRE (37%) and ERE (76%) were recorded at 1.25 g 100 g-1 dietary arginine. Maximum body protein (18.88 g 100 g-1) and RNA/DNA ratio (5.20) were also obtained in a 1.25 g 100 g-1 arginine dry diet. Except for the reduced growth performance in fish fed arginine-deficient diets, no other deficiency signs were apparent. Based on the broken-line and second-degree polynomial regression analysis of the AWG, SGR, FCR, PER, PRE and ERE data, the optimum arginine requirement for fingerling Labeo rohita was found to be in the range of 1.22-1.39 g 100 g-1 of the dry diet, corresponding to 3.05-3.47 g 100 g-1 of dietary protein.