Induced ovulation by injection of 17,20 beta-dihydroxy-4-pregnen-3-one in the artificially matured Japanese eel, with special reference to ovulation time

The effects of injection of 17,20 beta-dihydroxy-4-pregnen-3-one (DHP) on induced ovulation in the artificially matured Japanese eel Anguilla japonica were examined, with special reference to the effect of injection time on the time of ovulation. Ovulation occurred 18 h and 21 h after injection of DHP at 9:00, in 10 of 15 females and in the remaining 5 females, respectively. Injection of DHP at 18:00 induced ovulation 15, 18, and 21 h after injection in 4, 12, and 2 of 18 females, respectively. Fertility and hatching rates were not significantly different between females which ovulated 18h after injection at 9:00 or 18:00. In the second experiment, eggs from females which ovulated 15 h after DHP injection showed significantly higher fertility (about 63%) and hatching rates (about 54%) than eggs from females which ovulated 18 h after the injection. These results indicate that the time of ovulation depends on the time elapsed after the DHP injection in the eel.