Arginine requirement of juvenile Japanese flounder Paralichthys olivaceus estimated by growth and biochemical parameters

Abstract

Growth performance and different biochemical parameters were evaluated to estimate the arginine requirement of juvenile Japanese flounder, by feeding purified diets containing 50% crude protein from casein, gelatin and l-crystalline amino acids (CAA). CAA were supplemented to correspond to the amino acid pattern found in the whole body protein of the Japanese flounder except for arginine. Diets with six graded levels of arginine (from 1.25% to 3.25% of diet) were fed to triplicate groups of the juveniles (1.85±0.05 g) twice a day for 40 days at 5% of body weight. To prevent leaching losses, CAA were pre-coated with carboxymethylcelloluse (CMC) and diets were further bound by both CMC and k-carrageenan. After the feeding trial, plasma-free arginine and urea levels, excreted ammonia–N and urea–N in the water and liver arginase activity were analyzed to compare the result of the growth studies. Percent survival, specific growth rate, feed conversion efficiency and apparent protein retention were significantly ( P<0.05) affected by dietary arginine concentrations. The arginine requirements of Japanese flounder based on broken-line analyses of percent weight gain and feed conversion efficiency were 2.04% and 2.10% of diet, respectively. Plasma urea level and arginase activities in the liver were also closely related to different levels of arginine intake by the Japanese flounder. The requirement values obtained from the biochemical parameters were similar to the estimated value based on growth data, but those estimated based on excreted ammonia–N and plasma-free arginine level gave a slightly higher requirement value (2.45% of diet) of the Japanese flounder.