1998 Volume 33 Issue 5 Pages 455-458
In southern part of Kyusyu, Japan, a disease with mortality has repeatedly occurred in the farmed yellowtail Seriola quinqueradiata and amberjack S. dumerili in the early summer since 1989. The affected fish, most of which weighed less than 100 g, had no specific external signs. After the dissection, reddening of the brain was noticed in all the diseased fish. Remarkable histopathological sign was meningitis across the brain and spinal cord in all the affected fish. However, no noticeable histological alteration was found in the visceral organ, gill and muscle. Bacteria-like particles were found in stamps of the brains. A Gram-negative, short-rod bacterium was isolated from the brain of all the diseased fish. Pathogenicity of the bacterium against yellowtail was confirmed by an experimental infection, but the taxonomy of this bacterium remains unknown. This is the first report on a bacterial infection in which the brain is the main target organ in a host fish.