Streptococcus sp., Pathogenic to Cultured Yellowtail, Isolated from Fishes for Diets

Abstract

The streptococcal infection of cultured yellowtail, Seriola quinqueradiata, occured since 1974, resulted in serious damages to yellowtail productions every year. It is important for taking preventive methods against this disease to make clear the sources of infection. Fresh and frozen fishes used for diets in farms of the fish were examined to detect the causative bacteria.
As the result, the causative bacteria, similar to Streptococcus faecalis and S. faecium, were isolated from several species of diet fishes. Yellowtails inoculated intraperitoneally with the isolates were killed with typical symptoms of this disease. The causative bacterium was found to be alive for over 6 months under low temperature, especially frozen condition.
It was suggested that the contaminated diets with the causative bacteria may be one of the sources of infection and significant of the propagation of this disease.