SEXUAL PHASES IN THE AMERICAN OYSTER (OSTREA VIRGINICA)

Abstract

Although this species is seasonally dioecious, the primary gonads are bisexual, the peripheral layer of cells consisting mainly of ovocytes, with spermatogenic cells adjacent to the lumens. In 3-30% of these individuals, varying with the locality, the primary gonad is transformed into an ovary; all the other individuals first function as [male] [male] in the localities investigated, although they still retain more or less numerous ovocytes. After spawning, the gonads are still bisexual, the residual cells forming the basis of subsequent changes in the sexual phase. Since the relatively few individuals which function as [female] [female] during their first spawning season have a mean size much greater than that of the more numerous [male] [male], and since the proportion of [female] [female] is fully 10 times as great where the environmental conditions, as indicated by rate of growth, are the most favorable, it is suggested that nutrition is an important factor in the differentiation of the sexual phase.