Effects of UV irradiation on embryonic development of different inbred strains of the fish Oryzias latipes.

Fish embryos/UV irradiation/Strain difference Embryos of three different inbred strains and one substrain of Oryzias latipes were irra diated with UV light (25 to 300 J/m2) at the morula stage. Dose-dependent decrease in the surviving fraction was observed in embryos of all strains when examined at optic bud forma tion stage (Stage 19). It differed, however, in extent among different strains examined. The strain most sensitive to UV light was HO4C, 50% survival dose being 50 J/m2 , whereas in HB32C (resistant strain) 50% survival dose as high as 150 J/m2 was found. The survival rates in embryos of all strains were increased by post-irradiation illumination with visible light, the photoreactivable fraction being 0.4 to 0.7. The survival of irradiated embryos when examined at hatching was lower than that examined at Stage 19 in all strains and in this case also, the highest sensitivity to UV of HO4C embryos was clearly demonstrated.