Abstract
Vertebral deformity occurred in cultured marine fish, yellowtail (Seriola quinqueradiata) at an occurrence rate of 2.1% from July to September, 1982 in Mie Prefecture. Eighteen deformed fish (11-15 cm in body length) were investigated with bacteriological, soft radiographical and histopathological technics. β-hemolytic streptococcal bacterium was dominantly isolated from the brain of the diseased fish and identified as Streptococcus iniae. The soft radiographical technic confirmed that the deformity was due to vertebral lordosis, kyphosis and scoliosis at the trunk and tail parts. The histopathology of diseased fish was characterized by a massive infiltration of cocci-laden macrophages and production of granulomas containing cocci in the third ventricle, maninges and granular layer of cerebellar cortex of the brain. There were also granulomas in the hepatec capsule and peritoneum.
