This study examined the time to ovulation in artificially matured Japanese eel following an injection of 17, 20 beta-dihydroxy-4-pregnen-3-one (DHP), and changes in fertilization and hatching rates at various times after ovulation. Thirteen females, showing body weight indices (body weight/initial body weight X 100) of 119 +/- 2.3% with oocytes at the migratory nucleus stage after 9-12 weekly injections of salmon pituitary extract (20 mg pituitary powder /fish/week), received an injection of salmon pituitary extract (20 mg/fish) followed 24 h later by a DHP injection (2 mu g/g BW) for induction of ovulation. Eleven of 13 females ovulated within 23 h of the final injection; two, seven, and two females ovulated at 14-17 h, 17-20 h and 20-23 h after the final injection, respectively, The remaining two did not ovulate within 26 h of the injection, Eggs from three out of the 11 ovulated females showed relatively high percent fertility (89.6-39.5%) and hatching rates (47.6-15.3%) when they were fertilized after the first detection of ovulation. Both percent fertilization and hatching rates of eggs retained in the body cavity decreased rapidly within 6-9 h after ovulation, These results indicate that ovulation induced by DHP treatment occurs after a short but well-defined period of time, and that artificial fertilization must be carried out immediately after ovulation in order to obtain good quality eggs.
