Abstract: The paper examined the conditions of diseases and pathological changes of fish to the natural infection of euteritis of grass carp, putting a sed of silver carp, rotting gill of grass carp, albinism of silver carp, haemorrhage of carp body surface infect and septicaemia of soft-shelled turtle infect. In the meantime, pathogeny was examined by using the materials of pathological changes. The result showed that all the infection were caused by Aeromonas. Through identifiying80 strains of isloated bacteria, the result showed A. hydrophila was 29 strains (36.25 per cent), A. sobria was 13 strains (16.25 per cent), A. caviae had38 strains (47.5 per cent), all of the diseases iufeeted by single or more pathogewic bacteria.

Key words: Fish, Aeromona, Infection, Examination