Hemolytic ascitesosis of allogynogenetic crucian carp occured rece-ntly both in the suburb of Shanghai and Wujian County (Jiashu Province). Experi-ments of isolation and artificial infection tests have been done and the virulent pat-hogenic bacteria strains such as N-1-2,89-7-14, D-Ⅱ-1 were available. Accordingto the morphological features of the bacterium, cultural characteristics,physiologicaland biochemical reacts, and the G+C Mol % of these strains, it was identified to be Aeromonas sobia and A. hydrophila of moving Aeromonas. By applying the methods of tachypleus amebocyte lysate, serum of five ill fishwhich were artifecally infected by N-1-2 strain has been given the qualitative ana-lysis of endotoxin, and the result is positive. The same experiment has been appliedto the serum of four other healthy fish, and the result is negative. Then the disrup-ted bacteria cell suspension of the strain is injected to healthy fish, the result ob-tained are the same as those caused by pathogeny cells infection, so it is consideredthat the pathogony during its growing, reproduction and self-dissolving within thefish produces and liberates such a substance as endotoxin which caused the fish di-sease.