Rapid Induction of Female-to-Male Sex Change in Adult Zebrafish by Injection of an Aromatase Inhibitor.

Previously, we examined whether aromatase inhibitor (AI) treatment induces a sex change in adult female zebrafish. A 5-month AI treatment regime resulted in the retraction of the ovaries and testis formation. Eight weeks after changing the diet to AI-free food, a large number of normal sperm were obtained. Artificial fertilization using sperm from the sex-changed females was successful. These results demonstrated that sex plasticity remains in the mature ovaries of zebrafish. However, >7 months of treatment was necessary; thus, pairing was unsuccessful. In this study, we tried to induce sex change through the injection of an AI to shorten the time course of sex change. When the AI solution was directly injected into the abdomen of zebrafish, retraction of the ovary was induced within 2 months. The natural mating of sex-changed females with normal females was successful at 3 months. Although the fertilization rate was low, juveniles resulting from these matings developed normally. We succeeded in establishing a method for inducing sex changes in adult zebrafish within 3 months. The procedure will support the study of how sexual plasticity persists in adult zebrafish following sex differentiation and the identification of undifferentiated stem cells.