| The amino acid arginine has important nutritional and physiological roles, and it is indispensable in the diet of many fish species. Studies with other animal species have indicated that renal synthesis of arginine can be a major endogenous source of this amino acid. Arginine is also used by macrophages, the main phagocytic cells, to synthesize nitric oxide, which has cytotoxic actions on various pathogenic organisms.; In aquaculture, infectious diseases frequently occur and result in substantial economic losses. Current methods of disease control are expensive, highly regulated and not always effective. In this study the dietary manipulation of arginine was evaluated as an alternative to control infectious disease in channel catfish. Four separate experiments were conducted to reevaluate the dietary arginine requirement of channel catfish and examine endogenous arginine synthesis, as well as to evaluate the effects of dietary arginine levels on nitric oxide production of macrophages and disease resistance of fish after challenge with the pathogenic bacteria Edwardsiella ictaluri .; Based on weight gain and feed efficiency, the minimum dietary requirement of channel catfish for arginine was found to be similar to the previously determined requirement at 4.3% of dietary protein. At suboptimal levels of dietary arginine, dietary glutamate but not glycine appeared to contribute arginine through internally derived citrulline based on weight gain and plasma amino acid concentrations. Dietary glutamate was able to spare up to 30% of the requirement for arginine in channel catfish.; Cultured catfish macrophages synthesized nitric oxide in response to bacterial lipopolysaccharide at different rates depending upon composition of culture media. Nitric oxide production was increased when arginine, citrulline and arginine plus glutamine were used as substrates; arginine plus glutamine gave the most significant increase. Macrophage nitric oxide generation was inhibited by NG-monomethyl-L-arginine, suggesting an arginine-dependent metabolic pathway for production of nitric oxide in catfish. In addition, dietary arginine at a level twice that required for optimal growth, enhanced survival of catfish after challenge with E. ictaluri. Thus, results from these experiments provide fundamental information which may be useful in refining dietary formulations for better growth and survival of cultured channel catfish. |
