Sexual Plasticity Among Fish

Functional sex change as a natural part of the life history is found among a wide variety of fish taxa. However, this represents but a part of a continuum in sexual plasticity among fishes. Some gonochoric fish taxa have a gonad that develops as an ovotestis before resolving into either an ovary or a testis. Primordial germ cells appear to be bipotential in some fish species. In others, experimental transfer of spermatogonia into the ovary of a conspecific leads to de-differentiation and subsequent differentiation into oogonia. Somatic cells and tissues also have been shown respond differentially in response to the presence of either spermatogonia or oogonia. And disruption of pathways involved in the natural conversion of testosterone to estradiol during early development in genotypic females can lead to the development of a fully functional male phenotype. Ultimately, both endogenous and exogenous factors play important roles in plasticity of sexual phenotype among fish. The study of both naturally occurring sex change in hermaphroditic fish species and of phenotypic sexual plasticity in gonochoric species is slowly but steadily contributing to our understanding of determinants of lability of sexual function in fishes.