Dietary influences on disease resistance factors in channel catfish

The effects of diet on selected disease resistance factors were studied in channel catfish (Ictalurus punctatus). Two commercial feeds and a "control," laboratory-prepared diet were compared. Macrophage function (phagocytosis and intracellular killing) was used to assess nonspecific disease resistance and serum antibody was measured as an indication of specific immunity. We measured the immune response to Edwardsiella ictaluri, a common bacterial pathogen of catfish, as well as the phagocytosis and killing of the bacteria. In the initial experiment fish were maintained on the experimental diets for 116 days, vaccinated and responses assayed 14 days later. Significant differences among the groups were observed in the phagocytic index as well as in circulating antibody. An additional study showed that even when fed the experimental diets for only 42 days there were significant differences in the ability of macrophages from both immunized and nonimmunized fish to kill E. ictaluri.