Fishing gear-induced skin ulcerations in Baltic cod, Gadus morhua L

In 1982 a high prevalence of skin ulcerations was observed in Baltic cod in the vicinity of the Danish island of Bornholm. In March the prevalence varied from 6 to 13%, and in May it had increased to between 26 and 48%. The ulcerations had a sequential development. The initial stage appeared as severe skin abrasions in the area from the pectoral fin posterior to the level of the anus. The skin abrasions developed into large spots of necrotic dermal tissue with a diameter of 2-5 cm. The central part of the necrotic area sloughed off exposing a large haemorrhagic ulcer. Characteristically, most of the ulcerations on the trunk occurred bilaterally. A common histopathological finding was coagulation necrosis of the muscular tissue. The ulcerated fish were mainly 24-28 cm in length. A correlation between high concentrations of cod around Bornholm, high fishing activity in the area, length of fish escaping from the nets, combined with bilateral occurrence of the ulcers, strongly indicates that the skin ulcers were induced by the fishing gear. Features of the pathology could be linked to the temporary retention of cod in trawl meshes.