NEW OCCURRENCE OF EPIZOOTIC SARCOMA IN 

 CHESAPEAKE BAY SOFT SHELL CLAMS, MYA ARENARIA 



C. A Farley, 1 S. V. Otto, 2 and C. L. Reinisch 3 



ABSTRACT 



Maryland soft shell clams, My a arenaria, from Chesapeake Bay were sampled from 1969 through January 

 1983. Four cases of sarcomatous neoplasia were diagnosed histologically [1979 (1), 1982 (2), January 

 1983 (1)] in 3,584 animals. Hemocytologic sampling between December 1983 and May 1984 revealed 

 peak prevalences of 42-65% in clams from five sites. Sarcomas in laboratory-held clams progressed from 

 early to advanced stages and death. This is the first time epizootic neoplastic disease has been observed 

 in a wild molluscan population which was previously documented to be sarcoma-free. An infectious etiology 

 is implied and data indicate the potential for mass mortality of bay clams. 



Neoplastic diseases in soft shell clams, Mya arenar- 

 ia, have been reported from New England popu- 

 lations in both polluted and nonpolluted areas (Barry 

 and Yevich 1975; Farley 1976a; Yevich and Barszcz 

 1977; Brown et al. 1977, 1979; Brown 1980; Cooper 

 et al. 1982a; Reinisch et al. 1984). Generally, the 

 types of neoplasia noted have been considered as 

 having hemocyte (blood cell) (Yevich and Barszcz 

 1977; Brown et al. 1977, 1979; Brown 1980; Cooper 

 et al. 1982a; Reinisch et al. 1984) and gonadal (Barry 

 and Yevich 1975; Yevich and Barszcz 1977; Brown 

 et al. 1977, 1979; Brown 1980) origins or have been 

 designated as sarcomatous (Farley 1976a). A single 

 neoplastic clam was reported from Chesapeake Bay 

 with an apparent teratoma composed of nerve and 

 muscle tissue and digestive epithelium (Harshbarger 

 et al. 1977). Chesapeake Bay soft clams collected 

 and examined by several authors between 1971 and 

 1978 were free of the neoplastic disease (Barry and 

 Yevich 1975; Brown 1980) with the exception of 1 

 case found in a collection of 3,000 clams used as ex- 

 perimental controls (Brown 1980). Evidence for a 

 viral etiology for hematopoietic neoplasia in clams 

 was reported in a Rhode Island study (Oprandy et 

 al. 1981). Improved techniques such as examination 

 of hemolymph using a combination of histologic and 

 cytologic procedures (Cooper et al. 1982b) and the 

 development of a monoclonal antibody test specific 

 for neoplastic clam cells (Reinisch et al. 1983) have 

 facilitated the identification and diagnosis of the 

 disease. High prevalences of sarcomas have been 



■Northeast Fisheries Center Oxford Laboratory, National Mar- 

 ine Fisheries Service, NOAA, Oxford, MD 21654. 



2 Aspen Cove, Bozman, MD 21612. 



3 Tufts University School of Veterinary Medicine, Boston, MA 

 02111. 



found repeatedly in populations of Chesapeake Bay 

 clams. 



This paper documents the first occurrence of epi- 

 zootic sarcoma in soft shell clams in Chesapeake 

 Bay, and the first time neoplastic disease has ap- 

 peared in a wild molluscan population that was 

 previously shown to be free of the disease. Epizootic 

 prevalences of this condition may have a potential- 

 ly devastating impact on the clam industry of the 

 region. 



MATERIALS AND METHODS 



Sixty samples of 25 or more soft shell clams (total- 

 ing over 3,500 clams) have been collected periodi- 

 cally by the Maryland Department of Natural 

 Resources (DNR) or purchased from seafood outlets 

 from 51 sites in Chesapeake Bay since 1969. Each 

 animal was necropsied and tissues were fixed, pro- 

 cessed, and diagnosed histologically via standard 

 methods (Howard and Smith 1983) for diseases and 

 parasites. Recent samples (Table 1) were examined 

 by cytologic methods to determine the percent 

 prevalence and number of abnormal cells. Late 

 spring samples (YCLP, YSWP, YAGH, and YPIS, 

 Table 1) were diagnosed by both histology and histo- 

 cytology (technique described below). 



Hemolymph was drawn via hypodermic syringe 

 into sterile, ambient (15%o), artificial seawater to 

 produce a 1:9 dilution of cells to seawater. One milli- 

 liter of this sample was placed on a 25 mm, cham- 

 bered, poly-L-lysine coated microscope slide and 

 cells were allowed to settle for 1 h (the poly-L-lysine 

 coating improves the adhesiveness of neoplastic cells 

 which in vitro are rounded and do not usually stick 

 to glass [Cooper 1982a]). Fluid and chambers were 



Manuscript accepted May 1986. 



FISHERY BULLETIN: VOL. 84, NO. 4, 1986. 



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