ABNORMAL GAMETOGENESIS, MALE DOMINANT SEX-RATIO, AND SERTOLI-CELL MORPHOLOGY IN INDUCED TRIPLOID MUSSELS, MYTILUS-GALLOPROVINCIALIS

Gametogenesis of one year-old induced triploid mussels, Mytilus gallop rovincialis, was examined histologically and compared to sibling diplo id mussels. Histological analysis revealed that triploid mussels devel oped a number of primary spermatocytes that were arrested at prophase I. Late in the reproductive season, triploid mussels produced an extre mely small number of spermatozoa (9/10000 mu m(2) gonadal section) com pared to diploid mussels (1072/10000 mu m(2) gonadal section). All tri ploid mussels were identified as males, whereas the sex ratio of diplo id mussels was almost equal (1.12:1.0, male:female), indicating that s ex determination for this species may follow a Z:W model. Sertoli cell s in triploid mussels were prominent, had an enlarged cytoplasm, and w ere easily seen using light microscopy. In comparison, Sertoli cells i n diploids were thin and could only be seen by electron microscopy. Se rtoli cell hypertrophy in triploid mussels probably reflects their rol e in eliminating abnormal and degenerating germ cells.