SKIN ULCER DISEASE OF FLOUNDER PLATICHTHYS-FLESUS IN THE NORTHERN BALTIC SEA

Skin ulcer disease of flounder Platichthys flesus (L.) was investigate d at 7 sampling sites in the northern Baltic Sea, SW Finland, during 1 987-1989. Disease prevalences ranged from 1.8 to 11.1% in different ar eas. A significant correlation was established between sex, fish lengt h and disease prevalence. Males were more affected (10.7%) than female s (3.1%) and larger fish showed higher disease prevalences than smalle r ones. The length of the ulcerated flounders varied between 19 and 42 cm. The ulcers were not randomly distributed on the fish trunk. They occurred mainly on the blind side of the males and on the eye side of the females. Ulcers on males tended to occur close to the lateral line ; on females, the ulcers were scattered over the whole trunk. Bacteria l examination of diseased specimens resulted in the isolation of a cyt ochrome oxidase-negative, atypical Aeromonas salmonicida, primarily fr om the ulcers.