Effects of dietary arginine and lysine levels on growth performance and biochemical parameters of juvenile Japanese flounder Paralichthys olivaceus

To investigate the effects of disproportionate levels of dietary arginine and lysine on juvenile Japanese flounder Paralichthys olivaceus, growth performance and biochemical parameters were evaluated by feeding five test diets, comprising different levels of arginine and lysine, to triplicate groups of juveniles (initial bodyweight 1.85g) for 40 days. Crystalline amino acids were supplemented to test diets to correspond to the amino acid pattern found in the whole body protein of the Japanese flounder, except for arginine and lysine. After the feeding trials, plasma arginine, lysine and urea levels, excreted ammonia-N, and liver arginase activity were analysed. Survival, specific growth rate, feed conversion efficiency, and apparent protein retention were adversely affected (P<0.05) by the deficiency in dietary arginine or lysine concentrations. An excess of either lysine or arginine in the diet did not depress growth when the diets contained adequate levels of either arginine or lysine, proving that there is no evidence for an arginine-lysine antagonism. Results for plasma arginine, lysine and urea levels, excreted ammonia, and liver arginase activity also demonstrated that Japanese flounder juveniles are not sensitive to excess dietary levels of lysine and arginine.