Effects of elevated dietary arginine on resistance of channel catfish to exposure to Edwardsiella ictaluri

An experiment was conducted to assess the effects of elevated dietary argin ine on infection resistance to Edwardsiella ictaluri by juvenile channel ca tfish Ictalurus punctatus. Healthy channel catfish fingerlings were fed cas ein- and gelatin-based purified diets containing 28% crude protein and supp lemented with crystalline L-arginine at 0.5, 1, 2, or 4% of the diet. An in tact-protein diet containing 1.3% arginine also was included to investigate the effects of amino acid form (crystalline free amino acids versus intact protein). Each diet was fed to apparent satiation to triplicate groups of fish far 2 weeks. Subsequently, fish were exposed by immersion (1.3 x 10(8) colony-forming units/mL) to a virulent strain of E. ictaluri. Morbidity, m ortality, and cause of death were recorded during a 21-d period. Plasma ami no acid concentrations (14 h postprandial) 1 d before and 1 d after the bac terial exposure were analyzed via high-performance liquid chromatography. T he dietary concentration Of L-argainine significantly (P < 0.05) influenced mortality of fish because maximum survival after exposure to E. ictaluri o ccurred in fish fed the diet with 2% arginine. There was no additional impr ovement in survival rates after bacterial exposure by including a purified diet with intact protein. Circulating plasma amino acid concentrations indi cated an increased usage of arginine and glutamine in exposed fish. These r esults demonstrated a positive effect of an arginine-enriched diet on the r esistance of channel catfish to infection with E. ictaluri.