Abstract
An understanding of reproductive biology is critical for broodstock management of many cultured organisms, particularly those that are asynchronous hermaphrodites. For the silver-lip pearl oyster, Pinctada maxima, an understanding of gonad development, gender, and the environmental factors which may influence them is lacking. This study investigated quantitative aspects of sexual development in mature P. maxima, cultured at two sites and two depths at a commercial farm in Aljui Bay, Indonesia, and utilized multivariate statistics to assess variation in growth and development, along with relationships associated with environmental parameters. Comparisons of sex ratios in two age and size classes of oysters were also made to determine the effects of age and size, as well as culture conditions. Through macroscopic investigation of gonads and comparison with histological data, it was found that gonad color and appearance may be used to reliably determine sex and stage of development in P. maxima, without sacrificing the oyster. The majority of oysters observed were of indeterminate sex (58%); however, gametogenesis occurred between August and February, with spawning occurring twice during that period; once in October/ November and again in February. The sex ratio was overwhelmingly biased toward maleness (1:0.01), with no spatial difference in the sex ratio between oysters cultured at various sites and depths. The expression of maleness was weakly correlated with water temperature, pH, and rainfall, whereas there was no correlation between femaleness and environmental descriptors. Size, not age, was more important in determining the sex of P. maxima. These findings are useful for developing broodstock assessment and management guidelines to facilitate rapid selection of mature oysters for hatchery operations, as well as site selection for culture environments conducive to optimal reproductive development.