A chronic disease occurred in cultured ayu, Plecoglossus altivelis, from May to July in 1995 in Kyoto and Hiroshima Prefectures. Cumulative mortalities reached 16-30% during that period. One type of bacterium was isolated from the kidney of diseased ayu which characteristically showed pale gills, pale viscera, and swallen spleen and kidney. The isolates of the bacterium were confirmed to be pathogenic to ayu, Japanese flounder, Paralichthys olivaceus, and red sea bream, Pagrus major, by

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... cular injection. The organism was identified as a Pseudomonas species based on the biochemical properties.