A Comparison of Skin Tumors in Three Species of Flounders

Abstract

A study of the natural history of skin tumors occurring on two species of Pleuronectidae was conducted in the waters of Bellingham Bay, Washington. Twelve collections at monthly intervals indicated that 4.8% of 1977 English sole (Parophrys vetulus) and 2.4% of 2946 starry flounders (Platichthys stellatus) were tumorous. Three types of tumors were observed, and were classified as angioepithelial nodules, epidermal papillomas, or angioepithelial polyps, according to nomenclature previously established by other workers. The angioepithelial nodule was found on fish in the 1st year of life but not on fish older than 1 year. Epidermal papillomas usually occurred on fish that were 1 year or older, as did the angioepithelial polyps. The incidence of tumor-bearing fish, and the average number of tumors on a single specimen was greatest during the 1st year of life and decreased progressively in older age-groups. Tumors were more likely to occur on the pigmented side than on the nonpigmented side of the fish. The results of this study were compared and contrasted with a similar disease previously described on Hippoglossoides elassodon, the flathead sole.