Epizootiology of neoplasms in bony fish of North America.

Over the past 25 years, there have been an increasing number of fish tumor epizootics recognized in discrete geographical areas in North America. This is consistent with an association between tumor development in fish and exposure to waterborne contaminants as a result of increased industrialization. Reports of fish tumor epizootics from the literature, plus acquisitions at the Registry of Tumors in Lower Animals, Smithsonian Institution originate from 41 geographical regions in North America. Epizootics of hemic, neural, connective tissue, and gonial neoplasms seem unrelated to environmental pollution, but epizootics of hepatic and epidermal neoplasms appear to be caused or strongly influenced by environmental pollution. The 14 species with epizootic liver tumors are all bottom feeding fish, and tumor-bearing fish are generally located in areas where chemical contaminants are concentrated. Epidermal neoplasms are also found in fish near polluted areas, but a direct cause-and-effect link with chemical carcinogens is not clear.