Therapeutic attempt to control streptococcicosis in cultured rainbow trout, Salmo gairdneri, by using erythromycin

Application of erythromycin (EM) to control natural-occurring streptococcicosis caused by β-hemolytic Streptococcus sp. in cultured rainbow trout, Salmo gairdneri was investigated.β-hemolytic Streptococcus strains were isolated at high frequency from diseased and apparently healthy fish collected from the pond. These isolates indicated a strong sensitivity against EM at in vitro sensitivity test. Fish population transferred from contaminated pond were fed with pelleted food containing EM at a dose of 50 mg/kg/day for 5 days. After the drug was administered to the fish population for 5 days, the mortality was markedly reduced during the observation period. Therefore, EM was confirmed to be an effective drug for the control of streptococcicosis in cultured rainbow trout.