The dietary arginine requirement of channel catfish (Ictalurus punctatus) is influenced by endogenous synthesis of arginine from glutamic acid

Previous studies with young mammals have established that arginine synthesi s from glutamate-derived citrulline can be a major endogenous source of arg inine. Therefore, an experiment was conducted to re-assess the dietary argi nine requirement of juvenile channel catfish and to determine the metabolic effects of including glutamate or glycine to maintain isonitrogenous level s among diets. Two sets of diets were formulated to contain 24 g crude prot ein/100 g dry weight from casein/gelatin and crystalline amino acids with a rginine supplementation in 0.5 increments from 0.5 to 2.0 g/100 g diet. Ami no acid nitrogen was maintained equal, within sets, by replacing arginine w ith aspartate and either glutamate or glycine. Each diet was fed to apparen t satiation to triplicate groups of 12 fish initially averaging 11.4 g/fish for 8 weeks. Weight gain (WG), feed efficiency (FE), protein efficiency ra tio (PER), protein retention (PR) and survival were significantly (P < 0.05 ) affected by arginine. At the suboptimal level of dietary arginine, glutam ate appeared to contribute arginine through internally derived citrulline b ased on increased plasma citrulline and arginine concentrations. WG and pla sma amino acid concentrations of fish fed diets with glycine suggested that it does not serve as a precursor for citrulline. Based on WG and FE, juven ile channel catfish were found to require arginine at 3.3% to 3.8% of dieta ry protein, when glutamate was included in the diet. The requirement estima te was 33% higher when glycine replaced glutamate in the diet and was simil ar to the previously determined arginine requirement of channel catfish at 4.3 g/100 g of dietary protein. These results strongly suggest that dietary glutamate is used for endogenous synthesis of arginine in channel catfish, especially when arginine is deficient in the diet. (C) 2000 Elsevier Scien ce B.V. All rights reserved.