Tumours and microbial diseases of marine fishes in Alaskan waters

Abstract

Abstract. In an effort further to define the current health status of demersal fish in the Bering Sea, 36 618 fish captured by otter trawl during 1976 were examined for pathological conditions. Of the 26 species examined, 22 were found to have no detectable abnormalities. The four species with abnormalities were Pacific cod Gadus macrocephalus Tilesius with pseudobranchial tumours and skin lesions, walleye pollock Theragra chalcogramma (Pallas) with pseudobranchial tumours, yellowfin sole Limanda aspera (Pallas) with lymphocystis, and rock sole Lepidopsetta bilineata (Ayres) with epidermal papillomas. The prevalence, geographical distribution and biological and pathological characteristics of affected individuals were determined.Pseudobranchial tumours of both Pacific cod and walleye pollock were occasionally found to be invasive. Fish bearing these tumours were distributed throughout the sampling area. The epidermal papillomas on rock sole resembled similar tumours found on several flatfish species along the West Coast of North America. The distribution of this disease appeared to be depth related. The virus‐caused lymphocystis growths were located on the ‘blind’ side of yellowfin sole. The highest frequencies of fish with lymphocystis were in the south‐eastern Bering Sea. Two main types of skin lesions were seen on Pacific cod: ulcers and ring‐shaped lesions. Isolates of bacteria (Pseudomonas sp.) were routinely obtained from the cod ulcers and may be the cause of this disease. The ring‐shaped skin lesions, when examined microscopically, contained unidentified epidermal basophilic bodies.