Abstract
Since 1996, a new disease, which produces ulcers on the body surface or fins, has become prevalent in major producing areas of colored carp in Japan. Atypical Aeromonas salmonicida was isolated from ulcerative lesions of diseased fish in seven farms in Niigata Prefecture. Bacteriological characteristics of nine isolates were almost the same each other, but different from those of atypical A. salmonicida reported previously from ulcerative disease of goldfish. ln water-born exposure experiments of colored carp with the bacterial cells at a dose of 106 cfu/mL, all of the isolates induced high mortalities with formation of ulcerative lesions in the skin and fins.
