Abstract
From March to October in 1993, high mortality of more than 80% occurred among Kuruma shrimps, Penaeus japonicus (0.015-25.0 g in body weight) at farms in Hiroshima, Yamaguchi, Ohita, Kumamoto, Kagoshima and Okinawa prefectures in Japan. Abnormal red coloration or discoloration and white spot of the body were characteristic signs of the diseased shrimps.The high mortalities were noticed in all the shrimp farms that had imported juvenile Kuruma shrimps from China. This fact together with spreading pattern of the disease in shrimp farming areas suggested that the disease transmitted horizontally from the imported shrimps from China. No parasite or bacterium was found to be correlated with the disease. The disease was reproduced in healthy shrimps by injecting filtered (at 0.45μm) homogenate of lymphoid organ of spontaneously diseased shrimps, suggesting the disease was caused by a virus.
