“…Recently, toxicity testing using fish embryos has been recommended as a more humane form of animal testing (EU, ). However, we previously demonstrated that the embryonic and larval stages of zebrafish have different sensitivities to toxic chemicals (Horie, Yamagishi, Koshio, Iguchi, & Tatarazako, ; Horie, Yamagishi, Takahashi, et al, ), possibly because the chorion blocks the transport of certain chemical compounds (Kim & Tanguay, ; Olivares, Field, Simonich, Tanguay, & Sierra‐Alvarez, ). The results of the present study suggest that triclosan exposure negatively affects both the embryonic and the early larval stage in Japanese medaka, with a particularly steep increase in mortality soon after hatching, which is consistent with previous reports of delayed mortality in zebrafish exposed to the dioxin‐like pollutant PCB‐126 (3,3′,4,4′,5‐pentachlorobiphenyl) (Di Paolo et al, ) or to chlorinated anilines (Horie, Yamagishi, Koshio, et al, ).…”