Response to Challenge with Edwardsiella ictaluri by Channel Catfish, Ictalurus punctatus, Selected for Resistance to E. ictaluri

Abstract

Kansas strain channel catfish, "Ictalurus punctatus," is the oldest and most disease resistant domesticated strain of channel catfish. Kansas select line (selected for increased growth rate for two generations) was exposed to "Edwardsiella ictaluri," which caused an epizootic of enteric septicemia of catfish (ESC). Survivors were grown to sexual maturity. Their offspring were compared to offspring from Kansas select and Kansas random fish which had not been exposed to "E. ictaluri" (no ESC mortality had been observed in the parental fish that had been raised in a separate location) for their resistance to "E. ictaluri." The group selected for resistance to ESC and the two controls were challenged with "E. ictaluri" in two experiments (mean body weight of 38.9 g for test fish in experiment 1 [Kansas select controls] and 13.7 g in experiment 2 [Kansas random controls]) by bathing the fish in 1.1 X 10⁶ and 9.8 X 10⁷ "E. ictaluri" cells/ml for 1-2 hours in experiments 1 and 2, respectively. The two groups were challenged both communally and separately. The mortality of the F₁ selected fish and the F₁ controls (86.7% and 92.1% in experiment 1 and 51.4% and 44.3% in experiment 2, respectively) were not different (P > 0.05). The antibody titers prior to the initiation of the experiment were higher for the control groups than in the selected line. One generation of selection for resistance to ESC did not improve resistance to ESC in Kansas strain channel catfish. Mean antibody titer differences between the two groups prior to initiation were not correlated to resistance to "E. ictaluri."