Experiments on Induction of Protection against Kuchijirosho of Tiger Puffer

Kuchijirosho (snout ulcer disease) is an infectious disease of tiger puffer Takifugu rubripes, but little is known about detailed characteristics of its causative agent. Homogenate of brain from naturally diseased fish containing the kuchijirosho agent was treated with 0.3% formalin for 7 days. Injection of the homogenate induced 79% mortality in tiger puffer rearing at 25℃, indicating that the kuchijirosho agent was not inactivated by the formalin treatment. However, no mortality was observed in fish injected with the formalin-treated homogenate rearing at 18-20℃. A challenge test at 25℃ with the untreated homogenate showed that the formalintreated homogenate did not induce protection against kuchijirosho in the survivors.