Four hundred and forty five isolates of Edwardsiella tarda were collected on field surveys in eel culture ponds in Shizuoka Prefecture in 1980 and 1981. Two hundred and seventy isolates (61%) were classified, according to O-agglutination test, into four serotypes (A, B, C and D). There were no great differences in the composition of the serotypes among the following three kinds of samples; rectum contents of eel, eel pond water and pond sediments (A: 13-17%, B: 22 35%, C: 4-13%, D: 2-4%). However, serotype A was predominant in kidney samples (A: 72%, B: 0%, C: 3%, D: 13%). By experimental infection to eel, tilapia and loach, serotype A of E. tarda proved highly virulent to the fishes, especially to eel, in comparison with the other serotypes tested.
In October 1982, a bacterial disease occurred among cultured young flounder, Paralichthys olivaceus, in the Kurida Bay, Kyoto Prefecture. The diseased fish showed abdominal inflation and accumulation of ascites. Bacteria isolated from the diseased fish were identified as Edwardsiella tarda. The pathogenicity of the isolate for flounder and yellowtail, Seriola quinqueradiata, was proved positive by intra-peritoneal and/or intramuscular injections.
From July through September 1982, an epizootic occurred in a population of young cultured red sea bream, Pagrus major, in Nagasaki Prefecture. Some moribund fish without any significant lesions (average body weight 10 g) were submitted to bacteriological examination. The organism isolated from the kidney or spleen of the specimens was identified as Pasteurella piscicida. The characteristics were identical to those of the isolates from pseudotuberculosis in cultured yellowtail, Seriola quinqueradiata, in Nagasaki Prefecture in the period 1980-1982. The present isolate showed pathogenicity not only for red sea bream but also yellowtail, and LD50 for red sea bream was between 0.001 mg and 0.01 mg cells per fish. The injection of the isolate caused consistently white spots in the internal organs of yellowtails, whereas their formation in red sea breams was scarcely observed.