THE OCCURRENCE OF HISTOCHEMICAL ACTIVITY OF 3β-HYDROXYSTEROID DEHYDROGENASE IN THE DEVELOPING TESTES OF POECILIA RETICULATA

In the mature testes of the guppy, Poecilia reticulata , some groups of cells, distributed sparsely in the interspace between the peripheral germ cell layer and the hilar duct system, show evident histochemical response for Δ⁵-3β-hydroxysteroid dehydrogenase (3β-HSD). In the testis of newly delivered guppies, somatic cells are present in the testicular hilus as a compact mass without revealing any structural differentiation. In the testis of juvenile fish of the 8mm stage about 7 days after birth, interstitial cells resembling histologically those of adult testes become differentiated from the somatic cell mass and, though only in some specimens, coincidentally begin to display weak but obvious histochemical response for 3β-HSD. Thereafter the occurrence of enzyme activity becomes increasingly regular in the developing testes, and attains the adult pattern of distribution in testes of all specimens after the 11 13mm stage or 17 ∽ 20 days of age.
The appearance and enhancement of 3β-HSD activity in the testis is concurrent with the differentiation and development of the testicular duct system. Treatments of newly delivered fish with methyltestosterone (30 ∽ 50 μg/g diet) distinctly stimulate the development of the duct system, which suggests a possible role of androgen secretion occurring in the early phase of the testicular development in the control of testicular organogenesis in the guppy.