In female fish, no changes in the phenotypewere observed in the gonads of fish fromeither the virgin- or marine-plastic treatment. In male fish, we observed what appeared to be abnormal growth of germ cells throughout the testicular tissue of one male fish from the marineplastic treatment (Fig. 2) and no changes in fish from the virginplastic treatment. As the proliferation of germ cells is one of the initial steps of gametogenesis, normal germ cell proliferation is essential for successful reproduction (Saito et al., 2007). In medaka, the proliferation