Enteric Septicemia Resistance in Blue Catfish and Three Channel Catfish Strains

Seven full-sib families in each of three strains of channel catfish Ictalurus punctatus (mean weight, 10.7 g; SD, 2.6 g) and one family of blue catfish I. furcatus (mean, 10.9 g; SD, 0.4 g) were challenged by immersion with the bacterium Edwardsiella ictaluri, the causative agent of enteric septicemia, to evaluate variation in disease resistance. Blue catfish were resistant to infection and had only 0.7% mortality. Significant (P < 0.001) variation in channel catfish resistance was found among strains, families, and body weights. Red River strain channel catfish were the most resistant (14.9% mortality), followed by Mississippi-select fish (67.1%) and Mississippi-normal fish (72.3%). Mean family mortality of channel catfish ranged from 1.3% in a Red River family to 95.3% in a Mississippi-select family. Although weight had a significant effect on survival, the regression slope of survival on weight was −0.10 (SE, 0.02). Sources of variation in channel catfish mortality adjusted for weight were 67.3% from strains, 29.7% from families, and 3.0% from replicate tanks. The mechanism for differential resistance presently is unknown. Results indicate considerable potential for reducing disease losses by using E. ictaluri-resistant catfish strains in aquaculture and for genetic improvement in resistance via selective breeding programs.