Morphological and physiological studies on sex change in tropical fish: Sexual plasticity of the ovaries of hermaphroditic and gonochoristic fish

To clarify the role of estrogens in the onset of sex change in fish, estrogen levels were artificially reduced in hermaphroditic and gonochoristic female fish via the treatment with aromatase inhibitors (AIs). AI treatments caused depletion in blood estrogen levels and induced complete sex change from a female to a male in protogynous three-spotted wrasse and the honeycomb grouper. Opposite-direction sex change of the protandrous yellowtail anemonefish was also induced by AI treatments. Not only in hermaphrodites, AI treatments induced testicular differentiation and, in certain circumstances, a complete sex change in the developing ovaries of the gonochoristic fish: tilapia, medaka, zebrafish, carp and golden rabbitfish. We demonstrated that estrogen depletion induces the female to male sex change in both hermaphroditic and gonochoristic fish. Results suggested that some germ cells in the ovaries of both hermaphroditic and gonochoristic fish maintain sexual bipotentiality, which is the ability to differentiate into both female and male germ cells, throughout the life and that the fate of these germ cells' differentiation depends on the level of endogenous estrogen. Higher levels of circulating estrogen maintain femaleness, while lower levels force their differentiation into males. These studies contribute to the progress of aquaculture.