EFFECTS OF GONADAL NEOPLASMS ON OOGENESIS IN SOFTSHELL CLAMS, MYA ARENARIA

The average prevalence of gonadal neoplasms in softshell clams, Mya ar enaria, from Whiting Bay, Washington County, Maine, was 19.4% in 1994. Monthly prevalences ranged from 10 to 26.7%. Neoplasms ranged in inte nsity from few, small foci of undifferentiated germ cells (Stage 1), t o 50-100% of gonadal follicles being involved (Stage 2), to invasion a nd metastasis with loss of tissue architecture (Stage 3), indicating t hat the disease is progressive and lethal. There was no relationship ( P > 0.05) between prevalence of neoplasms and clam size between 45.7 a nd 60.7 mm mean shell length. Clams of both sexes were affected, but f emales were significantly more likely (P less than or equal to 0.025) to have neoplasms than males. Female clams with neoplasms produced sig nificantly fewer (P less than or equal to 0.001) gametes than healthy clams. Overall reduction of gamete number was 66%, resulting from dire ct displacement of gametes by tumor cells in affected gonadal follicle s. Compared to healthy clams, clams with neoplasms exhibited a signifi cantly lower (P less than or equal to 0.001) mean oocyte diameter befo re spawning and a significantly greater (P less than or equal to 0.001 ) mean oocyte diameter after spawning, as the result of a general (thr oughout the entire gonad) inhibition of normal oogenesis and spawning. It is concluded that gonadal neoplasms have a negative impact on the reproductive output of the Whiting Bay clam population. (C) 1996 Acade mic Press, Inc.