We evaluated the tissue persistence and live vaccine efficacy of five avirulent Edwardsiella tarda strains (E22, SU100, SU117, SU138, and SU244) isolated from the Japanese eel (Anguilla japonica) and from the environment. The live vaccines, containing a single strain, were injected intraperitoneally into Japanese flounder (Paralichthys olivaceus). Viable bacteria from all the strains (excluding SU100) were recovered from trunk-kidney tissue 28 d post-injection. Japanese flounder inoculated with E22 had the highest relative percentage survival (RPS=45%) in an artificial challenge with virulent E. tarda (NUF806). The serum of E22-vaccinated fish had a significantly higher agglutination titer against NUF806. In contrast,there was little or no increase in the agglutination titer of the fish that were inoculated with the remaining avirulent strains. Injection with avirulent E. tarda increased the expression of cytokine genes, including interleukin-1β (IL-1β), type 1 interferon (IFN), and IFN-γ in head-kidney of the Japanese flounder. Fish & Shellfish Immunology 29 (2010) 687-693. Tomokazu Takano, Tomomasa Matsuyama, Norihisa Oseko, Takamitsu Sakai,Takashi Kamaishi, Chihaya Nakayasu, Motohiko Sano, Takaji Iida. Aquatic Animal Health Division, National Research Institute of Aquaculture, Fisheries Research Agency, Mie 516-0193, Japan.