Effects of Elevated Dietary Arginine on Resistance of Channel Catfish to Exposure to Edwardsiella ictaluri

Abstract

An experiment was conducted to assess the effects of elevated dietary arginine on infection resistance to Edwardsiella ictaluri by juvenile channel catfish Ictalurus punctatus. Healthy channel catfish fingerlings were fed casein- and gelatin-based purified diets containing 28% crude protein and supplemented with crystalline L-arginine at 0.5, 1, 2, or 4% of the diet. An intact-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 for 2 weeks. Subsequently, fish were exposed by immersion (1.3 × 10⁸ colony-forming units/mL) to a virulent strain of E. ictaluri. Morbidity, mortality, and cause of death were recorded during a 21-d period. Plasma amino acid concentrations (14 h postprandial) 1 d before and 1 d after the bacterial exposure were analyzed via high-performance liquid chromatography. The dietary concentration of L-arginine significantly (P < 0.05) influenced mortality of fish because maximum survival after exposure to E. ictaluri occurred in fish fed the diet with 2% arginine. There was no additional improvement in survival rates after bacterial exposure by including a purified diet with intact protein. Circulating plasma amino acid concentrations indicated an increased usage of arginine and glutamine in exposed fish. These results demonstrated a positive effect of an arginine-enriched diet on the resistance of channel catfish to infection with E. ictaluri.