Disease of crucian carp has universally occurred in fish-farms in Shanghai suburbs and Jiangsu province since 1986. The disease makes very high incidence and mortality on the cultured fish. The important symptoms is that the infected fish appears, body surface congested,bug-eyed, anus swollen and red with inflated abdomen,and a great quantity of ascites in abdominal cavity. The histopa-thological inspection revealed that all diseased fish suffered from hemolysis, and serious anemia followed. Erythrocytes swollen and many red granular matters after dyed with H. E. presented in the cytoplasm. Hemolysis ocuured in whole viscera of diseased fish,all organs and tissues degenerated and necrosis, especially the liver, spleen and kidney.Although some papers have reported the diseased case of common carp, eel, channel catfish and salmon with much ascites and a very bulgy abdomen, but they didn't notice and mention the hemolysis, therefore, this fish disease is denominated to be hemolytic ascitesosis of crucian carp. The pathogens are Aeromenas sobria and A. hydrophila.