Abstract
The testes of the adult medaka, Oryzias latipes, reared in natural conditions of light and temperature, were examined histochemically for the occurrence of Δ5-3β-hydroxysteroid dehydrogenase (3β-HSD) in various periods of the annual reproductive cycle. In the testes of the fish, interstitial cells were present as clusters of varying numbers of cells, showing denser distribution along the region where seminal tubules conjoined with efferent ducts. In the period of active breeding of the fish, the testes exhibited an obvious histochemical response for 3β-HSD which was localized exclusively in the interstitial cells. During the sexually inactive period, the histochemical activity decreased in intensity as well as in number of responding cells, and was eventually indetectable in the testes until it reappeared in interstitial cells concomitantly with recovery of the spermatogenetic activity in the next breeding period. These results were not consistent with the histochemical observations made by Gresik et al.(1973), who could not reveal the histochemical activity of 3β-HSD in the testis of the medaka which were maintained continuously in a breeding state.
