Disease resistance and humoral antibody production in rainbow trout fed high levels of vitamin C

Young rainbow trout, Salmo gairdneri (1–10 g), fed test diets containing 1, 5, 10 and 20 times maximum growth requirements for L-ascorbic acid, and then challenged by injection or dip with Vibro anguillarum cultures, survived at varying rates, dependent upon the vitamin C intake. Significant differences appeared between dietary treatments in weight, growth rate, mortality and body vitamin C content. Resistance to bacterial infection and the humoral antibody production were assessed for the trout on various dietary treatments. Resistance to bacterial infection was directly related to vitamin C intake, and was reflected in improved survival of fish challenged and fed on 5, 10 or 20 times the normal vitamin C requirement for growth. Humoral antibody production was improved after 3–4 weeks on test, and persisted up to 10–12 weeks. Rainbow trout may survive bacterial challenge and improve humoral antibody production when fed 5 or 10 times growth requirement levels of vitamin C.