Epizootic neoplasms in fishes from a lake polluted by copper mining wastes.

Examination of fishes from Torch Lake, Houghton County, Mich., revealed epizootic neoplasms of several types in two closely related species. Saugers, Stizostedion canadense, and walleyes, Stizostedion vitreum, were commonly affected with hepatocellular carcinomas, dermal ossifying fibromas, and perivisceral masses resembling mesotheliomas that were usually associated with the mesenteric capsule of the spleen. Saugers were 100% affected with liver neoplasms. Histopathologic and ultrastructural aspects of the neoplasms are described. Torch Lake has been used as a repository for copper mining waste to the extent that an estimated 20% of the original volume has been filled in by these materials. Several direct and indirect etiologic roles for the mine waste as causative agents of the fish tumors are discussed.