This study investigated the effects of different doses of 17-β-estradiol (E 2) in Rhamdia quelen. Groups of males exposed to different doses of E 2 (0.1 mg kg − 1, 1 mg kg − 1 and 10 mg kg − 1) were compared with non-exposed male and female fish groups. Among the considered biomarkers, no significant differences were observed for micronuclei test, reduced glutathione concentration and lipid peroxidation. All E 2-treated individuals had decreased glutathione S-transferase activity. Increased catalase and superoxide dismutase activities, increased vitellogenin expression and decreased metallothionein concentration were observed in males treated with the highest dose. Liver of all test groups showed necrotic areas, but cytoplasm vacuolization was again found only in the individuals exposed to highest dose. E 2 causes deleterious hepatic effects to R. quelen, and vitellogenin expression, catalase and superoxide dismutase activity and metallothionein concentration represent appropriate biomarkers for studying E 2 effects. Additionally, the response of some biomarkers was similar in males exposed to E 2 and unexposed females, and therefore exposure to endocrine disruptors may cause consequences for fish populations.