An attempt was made to delineate the relationship between ofAeromonasspecies and/or serogroups and specific disease symptoms in common carpCyprinus carpioL. and rainbow troutOncorhynchus mykissWalbaum. The adhesion ofAeromonasstrains to various tissues in relation to disease spectrum was also tested. All strains ofA. hydrophilacaused skin ulcers as well as septicaemia in both carp and trout while the other strains were able to cause only skin ulcers or some specific internal lesions with or without septicaemia depending on which species and/or serogroup they represented. Disease symptoms depended also on fish species. It was found that adhesion intensity ofAeromonasstrains tested was significantly higher to tissues, which were susceptible to infection with these strains. The results indicate that adhesion to various cells of the fish organism is principal marker to detect virulentAeromonasstrains. The findings presented in this study may be helpful in the appraisal of aeromonads disease risk and kind of the infection in particular fish farms by epizootiological studies or/and during routine fish examinations. They will also be useful to improve and facilitate diagnosis of bacterial fish disease.