Effects of environmental stress (sex steroids and heat) during sex differentiation in Japanese flounder (Paralichthys olivaceus): insight from germ cell proliferation and gsdf-amh-cyp19a1a expression

Marine environments have been underwent many changes and threats due to human activities and climate variation. The available information regarding the effects of environmental changes on reproduction in marine fishes is limited. In this study, we investigated gonadal development with special attention on sex differentiation in genetically female Japanese flounders (Paralichthys olivaceus) larvae exposed to 17 beta-Estradiol (E2), 17 alpha-Methyltestosterone (MT) and heat treatment (27.5 +/- 0.5 degrees C) respectively from 30 to 120 dph. Results indicated that E2 obviously accelerated ovarian differentiation and inhibited germ cell proliferation, suggesting the exogenous estrogen was toxic to reproduction of genetically female fishes. The exogenous androgen and high temperature induced masculinization of genetically female flounders, accompanied by inhibiting the proliferation of germ cells. Meanwhile, the expression patterns of sex-related genes illustrated that the mechanisms of sex-reversal induced by high temperature and exogenous androgen may be different, with respectively inducing the high expression level of gsdf and amh, finally resulting in decreasing of cyp19a1a expression and masculinization of XX flounders. These results would be useful to assess and understand the influence of aquatic environmental factors on reproduction in teleost.