Skin ulcer disease of flounder Platichthys flesus in the northern Baltic Sea

Skln ulcer disease of flounder Platichthys flesus (L.) was investigated a t 7 sampling sites in the northern Baltic Sea, SW Finland, dunng 1987-1989. Disease prevalences ranged from 1 8 to 11.1 % in different areas. A significant correlation was established between sex, fish length and disease prevalence. h4ales were more affected (10 7%) than females (3.1%) and larger flsh showed higher disease prevalences than smaller ones The length of the ulcerated'flounders vaned between 19 and 4 2 cm. The ulcers were not randomly distributed on the fish trunk They occurred mainly on the b l ~ n d side of the males and on the eye side of the females. Ulcers on males tended to occur close to the lateral hne; on females, the ulcers were scattered over the whole trunk. Bacterial examination of diseased specimens resulted in the isolation of a cytochrome oxidase-negative, atypical Aeromonas salrnonicida, primarily from the ulcers.