• Endocrine disruptors;
  • Sex differentiation markers;
  • Ethinylestradiol;
  • Pejerrey


In pejerrey (Odontesthes bonariensis), ovarian differentiation has been associated with gonadal aromatase expression. It is also known that exposure of pejerrey larvae to estradiol (E2) produces all female populations. During the last few years, the presence of ethinylestradiol (EE2), a synthetic E2 analogue, has been reported in water reservoirs of different parts of the world. In the present study, the effects of EE2 were assessed on sex ratio bias and gene expression levels of gonadal aromatase (cyp19a1a), 11β-hydroxysteroid dehydrogenase type 2 (hsd11b2), estrogens (erα, erβ1), and androgen receptors (arα, arβ). Pejerrey larvae were fed with commercial food containing EE2 (0.1 and 1 µg/g) and E2 (50 µg/g) as a positive control for six weeks after hatching. The gonadal histological analysis showed that 42 to 46% of the fish had clearly differentiated ovaries in both the EE2- and E2-treated groups, compared with 27% in the control group. Moreover, in the EE2- (1 µg/g) and E2-treated groups, no fish presented signs of testicular development compared with controls. In addition, expression of cyp19a1a and hsd11b2 was significantly up- and downregulated, respectively, by EE2 and E2. The authors' results suggested that the feminization process driven by EE2 depends on the positive balance of cyp19a1a in relation to hsd11b2. Thus, these genes can be used as early indicators of exposure to xenoestrogens in this species. Environ. Toxicol. Chem. 2012; 31: 941–946. © 2012 SETAC