Effect of Estrogenic Activity, and Phytoestrogen and Organochlorine Pesticide Contents in an Experimental Fish Diet on Reproduction and Hepatic Vitellogenin Production in Medaka (Oryzias latipes)

Endocrine-disrupting chemicals (EDCs) are giving rise to serious concerns for humans and wildlife. Phytoestrogens, such as daidzein and genistein in plants, and organochlorine pesticides are suspected EDCs, because their chemical structure is similar to that of natural or synthetic estrogens and they have estrogenic activity in vitro and in vivo. We assessed estrogenic activity and dietary phytoestrogen and organochlorine pesticide contents of various fish diets made in the United Kingdom, and compared them with those features of diets made in Japan that were tested in a previous study. Genistein and daidzein were detected in all of the diets. Using an in vitro bioassay, many of these diets had higher activation of estrogen β-receptors than estrogen α-receptors. Organochlorine pesticides such as hexachlorobenzene, β-benzene hexachloride (BHC), and γ-BHC were detected in all fish diets. On the basis of these data, we investigated the effect of differing dietary phytoestrogen content in Japanese fish diets on hepatic vitellogenin production and reproduction (fecundity and fertility) in medaka (Oryzias latipes). Assessment of the effects of a 28day feeding period on reproduction of paired medaka did not indicate significant differences in the number of eggs produced and fertility among all feeding groups. However, hepatic vitellogenin values were significantly higher for male medaka fed diet C (genistein, 58.5 ± 0.6 μg/g; daidzein, 37.3 ± 0.2 μg/g) for 28 days compared with those fed diet A (genistein, < 0.8 μg/g; daidzein, < 0.8 μg/g) or diet B (genistein, 1.4 ± 0.1 μg/g; daidzein, 2.0 ± 0.1 μg/g). Our findings indicate that fish diets containing high amounts of phytoestrogens, such as diet C, have the potential to induce hepatic vitellogenin production in male medaka, even if reproductive parameters are unaffected. Therefore, some diets, by affecting vitellogenin production in males, may alter estrogenic activity of in vivo tests designed to determine activity of test compounds added to the diet.