Effects of gonadal neoplasms on oogenesis in softshell clams, Mya arenaria.
キーワード
概要
The average prevalence of gonadal neoplasms in softshell clams, Mya arenaria, from Whiting Bay, Washington County, Maine, was 19.4% in 1994. Monthly prevalences ranged from 10 to 26.7%. Neoplasms ranged in intensity from few, small foci of undifferentiated germ cells (Stage 1), to 50-100% of gonadal follicles being involved (Stage 2), to invasion and metastasis with loss of tissue architecture (Stage 3), indicating that the disease is progressive and lethal. There was no relationship (P > 0.05) between prevalence of neoplasms and clam size between 45.7 and 60.7 mm mean shell length. Clams of both sexes were affected, but females were significantly more likely (P = 0.025) to have neoplasms than males. Female clams with neoplasms produced significantly fewer (P = 0.001) gametes than healthy clams. Overall reduction of gamete number was 66%, resulting from direct displacement of gametes by tumor cells in affected gonadal follicles. Compared to healthy clams, clams with neoplasms exhibited a significantly lower (P = 0.001) mean oocyte diameter before spawning and a significantly greater (P = 0.001) mean oocyte diameter after spawning, as the result of a general (throughout 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.