Histology and histochemistry of the testis and ovary of the platyfish, Xiphophorus maculatus, from birth to sexual maturity.

The gonads of 3-day- to 7-month-old male and female platyfish (Xiphophorus maculatus) were examined for the presence of delta 5-3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and glucose-6-phosphate dehydrogenase (G6PD) by histochemical means. In 3-day-old males a positive response for both enzymes is localized in the Leydig cells. With subsequent testicular development, these cells increase in number and display greater activity at the periphery of the testis and around the efferent ducts. In 3-day-old females 3 beta-HSD and G6PD are localized in the stromal cells of the ovary. These cells increase in number and activity as the animals become sexually mature. Sertoli cells, efferent duct epithelium, and ovarian granulosa cells are negative at all stages of development examined. Our findings suggest that the gonads of neonatal fish possess the potential for steroidogenesis. The role played by sex-steroid hormones in the maturation of the brain-pituitary-gonad axis is discussed.