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In order to learn about factors that influence the reproductive cycle of marine bivalves, the levels of prostaglandins (PGs) PGE 2 and PGF 2α were measured during gametogenesis in the functional hermaphrodite scallop, Argopecten purpuratus. The PGs, in extracts of gonads of these scallops, were measured by radioimmunoassay techniques on different days after an induced spawning. To verify that gametogenesis was taking place during the experimental time, each time scallops were sampled, gonadal maturation was examined by gonadal index and by qualitative and quantitative histological analysis. Quantitative analysis involved oocyte size frequency distributions and determination of cross-sectional area occupied by mature sperm. The experiment was run twice, once in winter and once in spring. A linear decrease of both PGs was detected in male and female portions of the gonads as the maturation of these proceeded. In the spring experiment, this decrease was detected in both gonadal portions, but in the winter experiment, it was detected only for the male portion and not for the female one. The histological analysis of the gonads showed that in winter, the female gametes did not mature, although the male gametes did. These results are indicative of an inverse relationship between gonadal maturity and PG levels.

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