Development of an in vivo anti-androgenic activity detection assay using fenitrothion in Japanese medaka (Oryzias latipes).

The effects of endocrine disruptors, including anti-androgenic chemicals, on aquatic environments have received increased attention in recent years. Currently, the method used to screen chemicals for anti-androgenic activity is called the androgenized female stickleback screen, and it was established by the Organization of Economic Cooperation and Development in 2011 using the three-spined stickleback. However, screening chemicals for anti-androgenic activity has yet to be established using Japanese medaka. Thus, the purpose of this study was to establish a screening method for anti-androgenic activity utilizing the number of papillary processes in Japanese medaka (Oryzias latipes) as an indicator of the chemical's anti-androgenic activity. Thus, at 35 days post-fertilization, medaka were exposed to fenitrothion, an anti-androgenic compound, for 28 days. In the control group, the formation of papillary processes was observed in XY medaka, but not in XX medaka. However, after fenitrothion exposure, the number of papillary processes was significantly decreased in a dose-dependent manner in XY medaka; in the 300 µg l-1 concentration group, four of 11 XY medaka showed no papillary processes even if there were no significant effects on total length and wet body weight compared with the control group. Our results indicate that the number of papillary processes in Japanese medaka can be used as an indicator of anti-androgenic activity and that this model may prove useful as a chemical screening method. Copyright © 2016 John Wiley & Sons, Ltd.