Responses of Channel Catfish Fed Organic and Inorganic Sources of Zinc toEdwardsiella ictaluriChallenge

Abstract

Young-of-year channel catfish Ictalurus punctatus were fed an egg-white-based purified diet supplemented with serial concentrations of zinc from organic (zinc methionine, ZnMet) or inorganic (zinc sulfate heptahydrate, ZnS) sources for 10 weeks and subsequently challenged with Edwardsiella ictaluri by 24-h immersion (106 cells/mL, 24 ± 1°C). Maximum weight gain occurred when fish were fed diets with 5 mg of Zn/kg from ZnMet or 30 mg of Zn/kg from ZnS, and maximum bone zinc deposition occurred with diets containing 30 mg Zn/kg from either source. All fish fed the diet without zinc died following E. ictaluri challenge, whereas fish fed a sufficient amount of zinc showed 25–30% mortality. The amount of zinc required for maximum survival was 5 mg of Zn/kg of diet from ZnMet or 30 mg Zn/kg from ZnS. The zinc requirement for maximum antibody titer against E. ictaluri by channel catfish was 15 mg/kg from ZnMet or 30 mg/kg or more from ZnS. This study showed that dietary zinc influences the resistance of channel catfish to E. ictaluri challenge and that ZnMet is three to six times more potent than ZnS in protecting channel catfish against this pathogen.