JOURNAL OF INVERTEBRATE PATHOLOGY 52,436+l6 (1988) Gonadal Neoplasms in Hard Shell Clams Mercenaria spp., from the Indian River, Florida: Occurrence, Prevalence, and Histopathology DONALD M. HESSELMAN,’ NORMAN J. BLAKE, AND ESTHER C. PETERS~ Department of Marine Science, University of South Florida, St. Petersburg, Florida 33701 Received November 30, 1987; accepted April 26, 1988 The presence of gonadal neoplasms in hard shell clams Mercenaria spp., from the Indian River, Florida, was investigated over a 2-year period. Histopathological examinations of 1263 clams revealed an annual mean incidence of gonadal neoplasms in 11.6% of the population. Peak prev- alences appeared during the summer months. Microscopically, the tumors were seen as prolifer- ations of atypical germ cells arising from the germinal epithelium of the follicles, often completely tilling the lumen of both male and female follicles. In one female clam, the neoplastic cells invaded the connective tissue, muscle tissue, and the ground substance of the stomach and typhlosole. Electron microscopy confirmed the germ cell origin but did not reveal any viral particles. This is the first reported occurrence of a neoplastic disease in Mercenaria spp. from the southeastern United States. 0 1988 Academic Press, Inc. KEY WORDS: Mercenaria spp.; hard shell clams; histopathology; neoplasia; gonadal neoplasia. INTRODUCTION Within the past 20 years, numerous cases of neoplastic diseases of marine molluscs have been reported (see reviews by Pauley, 1969; Sparks, 1985; Mix, 1986). Research has focused primarily on the disseminated sarcoma of possible hemic origin affecting the soft shell clam, Mya arenaria (Brown et al., 1977; Yevich and Barszcz, 1977a; Oprandy et al., 1981; Cooper et al., 1982; Farley et al., 1986), oysters, Crassostrea virginica, C. gigas, and Ostrea lurida (Far- ley, 1969a; Jones and Sparks, 1969; Farley and Sparks, 1970), and the mussel Myths edulis (Farley, 1969b; Cosson-Mannevy et al., 1984; Rasmussen, 1986). Four occurrences of neoplasia of germi- nal origin have been reported. These in- clude one case of possible gonadal neopla- sia in M. edulis from British Columbia (Cosson-Mannevy et al., 1984), three cases in C. virginica from the Delaware and Chesapeake Bays (Farley, 1976; Harsh- barger et al., 1979), and in l-22% of M. arenaria from an oil spill site in Maine ’ To whom all correspondence should be addressed. ’ Registry of Tumors in Lower Animals, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560. (Yevich and Barszcz, 1977a). In this last report, the authors noted invasion and me- tastasis of the neoplastic cells to the sur- rounding connective tissue, kidney tissue, gills, and the genital and urinary pores. The only documented occurrence of go- nadal neoplasms in Mercenaria mercenaria came from the examination of 1300 clams collected from Narragansett Bay, Rhode Is- land, in which three females were afflicted with ovarian tumors (Yevich and Barry, 1969). The tumors were composed of ab- normal germ cells arising from the germinal epithelium of the follicles and ducts. The neoplastic cells proliferated, often filling the lumen of the follicles, and caused the arrest of gametogenesis. Although gener- ally restricted to the gonadal follicles, one female exhibited neoplastic invasion to the kidney area, red gland, and pericardial cav- ity (Barry and Yevich, 1972). The etiology of the tumors was not determined and no seasonal data were presented. This paper reports the first occurrence of gonadal neoplasia, similar to that described by Yevich and Barry (1969), in Mercenariu spp. from the Gulf of Mexico and south- eastern Atlantic coasts of the United States. Monthly samples over a 2-year pe- riod have allowed us to determine the sea- 436 0022-201 l/88 $1.50 Copyright 0 1988 by Academic Press, Inc. Au rights of reproduction in any form reserved.