Female eelpouts (Zoarces viviparus L.) are exposed during early pregnancy to nominal concentrations of 100 µg/L of 4-tert-octylphenol (OP) or 0.5 µg/L of 17-estradiol (E2). Effects on maternal metabolism and on liver and gonad development in embryos were examined and compared with controls (C) during exposure and after transfer to clean water (depuration). In the mother fish, significantly higher concentrations of plasma vitellogenin (vtg) and calcium were found in the two exposed groups, when compared with the C group after exposure and depuration. When compared, however, with the respective values after exposure, vtg had decreased significantly after depuration. The hepatosomatic index was normalized after depuration. In both exposed groups, the hepatocytes were rounded and not distinctly polygonal as in the controls. The amount of glycogen was considerably less while the number of mitochondria increased, and the rER significantly proliferated after exposure as well as after depuration. The gonads of nine of more than 28 embryos in the group treated with OP exhibited a number of abnormalities as compared with the normal gonad development in both sexes. Feminization of the male gonads in the exposed specimens and a number of histopathological features were observed in all the abnormal gonads, whereas reliable male features, such as formation of seminiferous tubules or spermioduct, were not observed. This study showed that 4t-tert-OP and 17-estradiol exert estrogenic effects during very early development of the embryos and that depuration had a positive effect on the motherfish and her embryos. J. Exp. Zool. 313A:399-409, 2010. © 2010 Wiley-Liss, Inc.