Evidence of small modulation of ethinylestradiol induced effects by concurrent exposure to trenbolone in male eelpout Zoarces viviparus

The interaction of xenobiotics is common in aquatic ecosystems; therefore, we wanted to evaluate if trenbolone (TB) modulates the effects of 17α-ethinylestradiol (EE2). Male eelpout (Zoarces viviparus) were exposed to 5 ng L−1 EE2 continuously for 19 d (EE2-C) or discontinuously (11 d, EE2-D) alone or in combination with low (50 ng L−1, TBL) or high (500 ng L−1, TBH) concentrations of TB (19 d). Exposure to EE2 caused reduced gonadosomatic index, increased plasma vitellogenin concentrations, up-regulated vtg and era mRNA expression and severe alterations in gonadal histology. TBL and TBH did not affect plasma vitellogenin, era or vtg mRNA expression. TBL and TBH did not counteract the EE2-induced increase in plasma vitellogenin and reduction in 11-ketotestosterone whereas TBH counteracted the EE2 induced increase in vtg and era mRNA expression. Exposure to TBH and EE2-C + TBH lead to severe gonadal histology alterations. TBL and EE2-D + TBH exposed fish showed less histopathological alterations. •EE2 caused increased plasma VTG and severe alterations in gonadal histology.•Exposure to EE2 caused up-regulated vtg and era mRNA in male eelpout.•TB modulated the EE2-induced era mRNA expression after discontinuous EE2-exposure.•High TB and continuous EE2 + high TB lead to severe gonadal histology alterations.•TB counteracted the histopathological alterations after discontinuous EE2-exposure. Trenbolone shows small modulation of EE2 induced effects in male eelpout (Zoarces viviparus).