Morphology of spermatogenic and accessory cells in the mussel Modiolus kurilensis under environmental pollution

A comparative light- and electron microscopic study of the male gonads of the bivalve mollusk Modiolus kurilensis from the reference and polluted sites in Amursky Bay (Sea of Japan) was conducted. Testicular acini in the mussels from the reference site had well-ordered structure (vertical spermatogenic columns located among the accessory cells bodies) whereas in the testes of the mollusks from the polluted site, the accessory and spermatogenic cell populations were disarranged. Mussels from the polluted station had about 26% of spermatogenic cells with marginal localization of nuclear chromatin, swollen outer nuclear membrane and heavily vacuolated cytoplasm and about 8% of spermatozoa with transformed or destructed acrosome; in mussels from the reference station, these values were close to zero. The accessory cells in the mussels from the polluted site were underdeveloped, and their phagocytic activity was inhibited. Our ultrastructural observations provide evidence that both spermatogenic and accessory cells are targets of environmental pollution in marine mussels.