Abstract
In ayu Plecoglossus altivelis fish farms throughout the country, the outbreak of streptococcicosis has recently become a problem especially to fish culturists and investigators. In this paper which deals with the investigation, infected ayu samples were collected periodically from the ponds of a farm, and the incidence of streptococcicosis and vibriosis were exmined with the lapse of time. Infiuence of medication on the outbreak of both diseases and mortality of the infected fish were investigated.
The result shows that the outbreak of streptococcicosis and vibriosis does not occur simultaneously in every pond. In one case, treatment with a dose of suppressive drugs of vibrioses shows increase in the outbreak of streptococcicosis, but decrease in vibriosis. On the other hand, after a dose of suppressive drugs of streptococcicosis was applied, the vibriosis spread increasingly while the streptococcicoses decreased in each pond.
