COOL WEATHER FEEDING INFLUENCES RESPONSES OF CHANNEL CATFISH TO EDWARDSIELLA-ICTALURI CHALLENGE

A pond study was conducted from November 1 through April 30 with young (age 0; average size, 43 g) and market-size (age-2; average size, 660 g) channel catfish Ictalurus punctatus to compare three management re gimens: no feeding, partial feeding (no feeding in December, January, and February), and continuous feeding according to fish size and water temperature. Weight change, feed conversion ratio, and responses to e xperimental challenge with Edwardsiella ictaluri were evaluated. No si gnificant difference in weight gain occurred between partially fed and continuously fed fish in either age-group; average weight increase fo r fed age-0 fish was 99% and for fed age-2 fish was 38%. The nonfed ag e-0 fish lost 12.3% and the nonfed age-2 fish lost 78 of their initial weight. Feed conversion ratios were significantly lower in partially fed fish than in continuously fed fish in both age-groups. Mortality f rom E. ictaluri challenge among age-0 fish was significantly higher in the nonfed fish, but among the age-2 fish, mortality was significantl y lower in the nonfed fish. No difference in mortality rate occurred b etween partially fed and continuously fed fish in either age-group. St arvation induced lower antibody production against E. ictaluri antigen in the age-0 fish but higher antibody production in the age-2 fish. P hagocytic index was lower in nonfed fish than in fed fish from both ag e-groups. This study indicates no benefit from feeding age-0 and age-2 channel catfish during December, January, or February if feeding is r eintroduced in March and continued through April. Although starvation was immunosuppressive in small channel catfish, it enhanced resistance to bacterial infection in larger fish. However, more research informa tion is needed before reduced feeding can be recommended to enhance re sistance of channel catfish to E. ictaluri.