Case of highly prevalent papilloma-like skin lesions in whitespotted char (Salvelinus leucomaenis) in Kamchatka (Russia).

In October 2014, a case of mass skin lesions was reported in whitespotted char (Salvelinus leucomaenis) caught in the Nalycheva River on the Kamchatka peninsula (Russia). The proportion of affected fish was approximately 50% of the catch. Lesions of varying severity were noted from small tubercles to large single and confluent formations and ulcers. Papilloma-like growths were found in the epidermal layer of the skin of the affected fish. Histopathological alterations included the following: submerged growth of epithelial cells, infiltration of inflammatory cells, oedema of scale pockets, resorption of scales, haemorrhages, local necrosis and an increased number of mucous cells. In the dermal layer of the skin, haemorrhages and extensive necrosis were recorded. Inflammation, necrosis and destruction of myocytes were found in the underlying musculature. This is the first documented case of papilloma-like skin lesions found in salmonids in Kamchatka. The affected whitespotted char were deemed unsuitable as a food product due to their unsatisfactory appearance and impermissible levels of bacterial contamination of the muscles.