The Riddle of Hepatic Neoplasia in Brown Bullheads from Relatively Unpolluted Waters in New York State

Since 1985, pathologists at Cornell University have investigated the causes of lesions in freshwater fish throughout New York waters in order to clarify possible impairment of fish health by environmental contaminants. Fishermen and biologists alerted us to several relatively protected reservoirs and ponds in which we have found no evidence of elevated levels of anthropogenic environmental contaminants but in which up to 100% of brown bullheads exhibited skin neoplasia. Complete necropsies and histologic study revealed that over 30% of mature brown bullheads from some of these sites had benign or malignant hepatocellular or biliary liver neoplasia. Up to 50% of brown bullheads had benign or malignant liver neoplasia in other relatively unpolluted waters with no evidence of skin neoplasia in bullheads. Multiple samplings of brown bullheads from several of these sites have revealed puzzling variability in the prevalence of skin, liver, and other neoplasia in these fish populations. The cause of these striking epizootics of neoplasia in brown bullheads in unpolluted waters in New York State remains unclear. We hypothesize that natural carcinogens such as N-nitroso compounds formed in aquatic sediments or radon from geologic formations may contribute to epizootic fish neoplasia in New York waters.