Abstract
In the course of diagnostic works of diseased ayu, Plecoglossus altivelis, and amago, Oncorhynchus rhodurus var. macrostomus, cultured in freshwater ponds in Tokushima Prefecture from 1977 to 1978, a new bacterial disease was found among them.
The characteristic sign of the diseased fishes was hemorrhagic lesions of body surface, especially operculum, abdomen, and anus.
A β-hemolytic streptococcus was isolated from these diseased fishes, and it proved to be able to kill ayu and amago with typical symptom of this disease by intraperitoneal injection. From the results of biochemical and biological tests, it became evident that the etiological agent of this disease was identical with the isolate from cultured yellowtail, Seriola quinqueradiata, by MINAMI et al. (1979). Yet, the species name could not be determined for the organism, because the antigen prepared from the isolate did not react with commercial antisera to Streptococcus groups A, B, C or G.
