Quantitative enzyme histochemistry of steroid and glucuronide synthesis in testes and seminal vesicle, and its correlation to plasma gonadotropin level in Clarias gariepinus

In spawning Clarias gariepinus from the Hula Nature Reserve in Northern Israel, the mean value for the seminal vesicle somatic index (SVSI) had decreased as compared with that in prespawning fish, due to loss of seminal vesicle fluid. Mean gonadosomatic index (GSI), however, had increased, probably as a result of hydration, 3α-Hydroxysteroid dehydrogenase (3αHSD), 3βHSD and uridine diphosphoglucose dehydrogenase (UDPGD) reactions were demonstrated in interstitial cells of both testis and seminal vesicle. UDPGD reactions were also found in the epithelium of the seminal vesicle tubules. Quantitative determination of the enzyme reactions with a computerized image analysis system revealed that total activity of all three enzymes in interstitial cells of the seminal vesicle was distinctly stronger in spawning fish. Prespawning and spawning fish did not differ in total UDPGD activity in the epithelium lining the seminal vesicle tubules. In the testes of spawning fish, total 3βHSD activity was stronger and total UDPGD activity weaker than in prespawning fish, but total 3αHSD activity was not different. Plasma gonadotropin (GTH) levels in male catfish were low as compared with females. This level was significantly increased in spawning males and extremely high in ovulated female spawning fish. The findings point to marked changes in the production of steroids and glucuronides in the reproductive organ system during spawning, especially in the seminal vesicle. These changes are accompanied by elevated levels of circulating GTH.