The photoreactivation (PR) rescue and dark repair on survival were investigated in UV-irradiated hermaphroditic fish (Rivulus ocellatus marmoratus) embryos. The survival at hatched larval stage of UV-irradiated embryos was markedly decreased with dose dependent manner when visible light was not illuminated after irradiation. However, the illumination of visible light after UV-irradiation remarkably increased in survival of the embryos. To measure the time course of PR rescue and effective period of visible light illumination, the embryos were exposed to visible light either for various time periods or at various times after irradiation at the close of 320 J/㎡ UV-light. The embryos were recovered to the maximum level of survival by PR from UV-induced damage when they were exposed to visible light at least for 6 hours or longer. Full PR occurred until 30 min, but PR effect gradually decreased when interval between UV-irradiation and a PR light exposure was longer than 30 min. From 96 hr intervals no PR rescue was detected. Treatment with 2 mM caffeine for 48 hours after UV-irradiation slightly increased UV sensitivity of the embryos. The above results strongly suggest that R. ocellatus marmoratus embryos have the high ability of photoreactivation and some caffeine-sensitive dark repair system as well.