Hepatocellular Neoplasm in a Wild-Caught Sheepshead Minnow (Cyprinodon variegatus) from the Northern Gulf of Mexico

Abstract

The sheepshead minnow, Cyprinodon variegatus, is a widely distributed small fish species that inhabits estuaries and inshore waters from New England to northern South America. This species has been used extensively in aquatic environmental toxicity and carcinogenicity tests (Couch et al., 1981; Courtney and Couch, 1984). Hepatic neoplasms have been induced in the sheepshead minnow by exposure to several known chemical carcinogens including diethylnitrosamine (Couch and Courtney, 1987), methylazoxymethanolacetate (Hawkins etal., 1985), and dimethylbenz(a)anthracene (Hawkins et al., 1991). Because of its widespread distribution, limited home range, and proven sensitivity tocarcinogens, the sheepshead minnow appears to be a good candidate to serve as an in situ monitor of environmental carcinogens and other toxicants in coastal waters, especially those of the Gulf of Mexico and Caribbean Sea. To establish background information on the histopathological lesions in sheepshead minnows taken from the wild, we collected and examined specimens from an offshore site presumed to be free of chemical contamination. The present report concerns a hepatic neoplastic lesion, diagnosed as a hepatocellular adenoma, found in a wild sheepshead minnow. Neoplasms from wild sheepshead minnows or spontaneous neoplasms from laboratory specimens previously have not been reported.