Gonadal Steroid Metabolism in Vitro and Localization of 3β-Hydroxysteroid Dehydrogenase Activity in Xiphophorus helleri (Pisces, Teleostei, and Poeciliidae)

Xiphophorus helleri, the swordtail, is a viviparous freshwater teleost that reproduces throughout the year. Therefore, the synthesis of sex steroids may be different from that of seasonal breeding ovuliparous teleosts. Currently, no data are available on the swordtail steroidogenesis, and reports on related poeciliids are conflicting. By means of in vitro incubation with tritiated precursors, we obtained a profile of steroids produced in the male and female gonads. For later comparison with steroidogenesis during pregnancy, we investigated virgin females in the current study. We also performed enzyme histochemistry for 3 beta -hydroxysteroid dehydrogenase (3 beta -HSD) to localize the cellular sources of gonadal steroids and to investigate the substrate preference of this enzyme.