Fish full life-cycle testing for 17beta-estradiol on medaka (Oryzias latipes)

We studied the chronic effects of 17beta-estradiol (E2) on the reproductive status of medaka (Oryzias latipes) over two generations under continuous exposure to assess its hazard on this species. The exposure of parental (F0) medaka to E2 was begun on embryos within 12 h postfertilization and continued for up to 101 d; the assessment endpoints included embryological development, hatching, posthatch survival, growth, sexual differentiation, reproduction, and hepatic vitellogenin (VTG) levels under flow-through exposure to E2 at each mean measured concentration of 0.939, 2.86, 8.66, 27.9, and 92.4 ng/L. Eggs (F1) spawned from the F0 fish at 98, 99, and 100 d posthatch were also examined for hatchability, survival after hatching, growth, sexual differentiation, and hepatic VTG level until 59 d posthatch. In the F0 medaka, no concentration-related effect of E2 was observed on hatching, posthatch mortality, and growth. However, we observed abnormal sex differentiation, induction of VTG, and reproductive impairment in a dose-dependent manner. The lowest-observed-effect concentration and no-observed-effect concentration of E2 for these effects were 8.66 and 2.86 ng/L, respectively. In the F1 medaka treated with E2 at < or = 8.66 ng/L, however, dose-dependent effects were not observed in any parameter. The results indicate that E2 can have significant effects on reproductive potential of medaka at concentrations as low as 8.66 ng/L, suggesting that the ecological risk of E2 is higher than that of weak estrogens, such as nonylphenol and octylphenol.