Pathogenicity of atypical Aeromonas salmonicida isolated from colored carpCyprinus carpio suffering from a new ulcerative disease

Since 1996, a new disease, which produces ulcers on the body surface or fin s, has become prevalent in major producing areas of colored carp in Japan. Atypical Aeromonas salmonicida was isolated from ulcerative lesions of dise ased fish in seven farms in Niigata Prefecture. Bacteriological characteris tics of nine isolates were almost the same each other, but different from t hose of atypical A. salmonicida reported previously from ulcerative disease of goldfish. In water-born exposure experiments of colored carp with the b acterial cells at a dose of 10(6) cfu/mL, all of the isolates induced high mortalities with formation of ulcerative lesions in the skin and fins.