The fecundity and fertility of Medaka exposed to chronic gamma-radiation in their embryonic stages.

Medaka/Chronic ƒÁ-irradiation/Fecundity /Fertility Eggs of the medaka, Oryzias latipes, were irradiated continuously with 137Cs ƒÁ-rays at exposure-rates of 10, 100 and 1000 R/day from the morula stage to hatching. Newly hatched fry were transferred to non-irradiation field. At one year after hatching medaka were tested for their fecundity and fertility. When irradiated females were mated with unirradiated males, both the total number of oviposition and number of eggs per oviposition decreased with in creasing exposure-rate, whereas almost all the eggs laid were fertilized. However, a decrease in the hatchability of these "normal" eggs was observed in groups of 100 and 1000-R/day exposure-rate. When irradiated males were mated with unirradiated females, an increase in the number of abnormal eggs was obtained in groups of 100 and 1000-R/day exposure-rate, whereas no changes in both the total number of oviposition and number of eggs per oviposi tion were observed. No change in hatchability of the eggs in this group was also observed even when the highest exposure-rate, i.e., 1000 R/day, was applied.