Efficacy of a Live-attenuated Edwardsiella ictaluri Oral Vaccine in Channel and Hybrid Catfish

This study evaluated the efficacy of an oral live-attenuated Edwardsiella ictaluri vaccine against enteric septicemia of catfish (ESC) in channel and hybrid catfish. The vaccine was delivered one time orally by feeding fish a diet coated with an attenuated E. ictaluri isolate at four doses to deliver between 4x10(6) to 3.2x10(7) viable vaccine cells/g wet feed. Thirty-five days postvaccination, control and vaccinated fish were challenged with virulent E. ictaluri and mortality was examined for 30d postchallenge. Mortality of nonvaccinated hybrids (85%) and nonvaccinated channel catfish (73%) was similar but significantly greater than all groups of vaccinated fish. In channel catfish, a trend toward increasing mortality with decreasing dose was observed. Mortality of channel catfish vaccinated with the lowest dose (26.6%) was significantly higher than fish vaccinated with the highest dose (14.1%) but similar to fish vaccinated at the intermediate doses (17.5 and 19.4%). In contrast, mortality of four doses of vaccinated hybrid catfish was similar and ranged between 10.4 and 14.0%. The data demonstrate that the attenuated E. ictaluri vaccine at all four doses tested is effective at reducing ESC-related mortalities in hybrid and channel catfish.