During summer to witner in 1974, the streptococcal infection occurred among yellowtails cultured in coastal waters, and has given serious damages to yellowtail productions since then.
The causative organism is a α-hemolytic Streptococcus and similar to Streptococcus faecalis and S. faecium (KUSUDA et al., 1976).
In July 1976, however, another Streptococcus different from the above was isolated from yellowtails cultured at two fish farms in Wakayama Prefecture.
Two isolates were found to be a β-hemolytic Streptococcus and agreed well with S. equisimilis in main characteristics (Table 6). The organium is also different from Streptococcus isolated from other fishes; rainbow trouts, eels, golden shiners, menhadens in hemolysis and tolerance tests.
The strain isolated from the sample showing corneal opacity and pericarditis caused typical symptoms of this disease in pathogenecity tests. Therefore, present isolates may be responsible in part for this epizootic, too.