ABSTRACT
Known viral diseases of walleye are: epidermal hyperplasia, walleye dermal sarcoma, diffuse epidermal hyperplasia, and lymphocystis. Epidermal hyperplasia lesions are gently raised, translucent, mucoid-like patches that are more discrete and less granular than lymphocystis or dermal sarcoma lesions. Epidermal hyperplasia is confined to the epidermis where the growths are distinct from the lesions associated with diffuse epidermal hyperplasia, dermal sarcoma, and lymphocystis, and a presumptive diagnosis is made in the field. Histopathological examination is used to definitively identify the different virus-induced growths of walleye. Dermal sarcoma lesions may be confused with lymphocystis, but probably not with epidermal hyperplasia or diffuse epidermal hyperplasia. Walleye herpesvirus causes epidermal lesions which resemble thick areas of slime. They are flat, translucent growths with soft, swollen underlying tissue. The primary significance of epidermal hyperplasia, walleye dermal sarcoma, and diffuse epidermal hyperplasia in walleye is that their appearance renders the fish unacceptable to fishermen and consumers.
