Protective properties of egg yolk IgY containing anti‐Edwardsiella tarda antibody against paracolo disease in the Japanese eel, Anguilla japonica Temminck & Schlegel

Immunized hens are known to contain a high level of immunoglobulin Y (IgY) in their egg yolk. In this study, the present authors obtained anti‐ Edwardsiella tarda IgY (containing 20% specific IgY, agglutination titre, 1:128) from hens vaccinated by injection with formalin‐killed bacterin. The IgY was stable against eel digestive factors, and therefore, was orally administered with viable E. tarda to the Japanese eels and the efficacy of protection against E. tarda infection was evaluated. Orally administered IgY at a dose of 400mg fish ‐1 cleared E. tarda inoculated simultaneously at 10 5–6 CFU fish ‐1 from the intestine within 24h. Moreover, orally administered IgY at doses of 200 and 400mg fish ‐1 inhibited the penetration of E. tarda inoculated simultaneously at 10 4–6 CFU fish ‐1 into the liver and kidney via the damaged intestine. The fish orally administered with IgY showed reduced mortality. These results suggest that egg yolk containing anti‐ E. tarda IgY is effective in preventing edwardsiellosis.