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Experiments were performed to examine the response of sterol metabolism in diploid and triploid Japanese oysters Crassostrea gigas (Thunberg) that had been conditioned for sexual maturation or unfed for 30 days. Free sterols were extracted, separated, identified and quantified by gas chromatography and gas chromatography–mass spectrometry for pooled samples of ten oysters from each of six treatments (two reference controls, diploid unfed and conditioned, and triploid unfed and conditioned). Effects of feeding regimes on total sterol contents were observed and the metabolism of sterols is discussed. Both unfeeding and conditioning appeared to influence the sterol pattern. Unfeeding increased sterol content regardless of ploidy level, suggesting a mainly structural role for these molecules. Conditioning led to an even greater rise in sterol content, but in diploid oysters only. These changes are discussed with regard to gametogenesis. Further study is needed to determine whether any individual variations among oysters would have affected our data.

Gametogenesis of one year-old induced triploid mussels, Mytilus galloprovincialis, was examined histologically and compared to sibling diploid mussels. Histological analysis revealed that triploid mussels developed a number of primary spermatocytes that were arrested at prophase I. Late in the reproductive season, triploid mussels produced an extremely small number of spermatozoa (9/10000 μm2 gonadal section) compared to diploid mussels (1072/10000 μm2 gonadal section). All triploid mussels were identified as males, whereas the sex ratio of diploid mussels was almost equal (1.12:1.0, male:female), indicating that sex determination for this species may follow a Z:W model. Sertoli cells in triploid mussels were prominent, had an enlarged cytoplasm, and were easily seen using light microscopy. In comparison, Sertoli cells in diploids were thin and could only be seen by electron microscopy. Sertoli cell hypertrophy in triploid mussels probably reflects their role in eliminating abnormal and degenerat...

Summary We conducted a comparative stereological analysis of diploid and induced triploid Mytilus galloprovincialis germinal and storage tissue volume fractions along an annual cycle, concomitantly to the irnmunocytochemical study of cerebral insulin-like peptide (ILP) secretion. Germinal tissue developed to the same extent in diploids and triploids, while storage tissue disappeared with the same pattern in both populations. We present irnrnunocytochemical evidence of an ILP cycle for the first time in bivalves. Moreover, this cycle is closely related to gametogenesis and storage tissue cycles and presents the same features in diploid and triploid animals.