Gonadal alterations in male eelpout (Zoarces viviparus) exposed to ethinylestradiol and trenbolone separately or in combination.

To evaluate the interaction between 17β-trenbolone (TB) and 17α-ethinylestradiol (EE2) in relevant environmental concentrations, male eelpout Zoarces viviparus were exposed in a flow-through seawater-system for 21 days to 5 ng l⁻¹ EE2, 5 ng l⁻¹ or 20 ng l⁻¹ TB or to combinations of both compounds. The effects on hepatosomatic index (HSI), gonadosomatic index (GSI) and gonadal histology were studied. No significant effects on HSI were observed in any treatment; in contrast, decreased GSI was observed in males exposed to EE2 alone or in combination with TB compared to controls (p<0.05). The histology revealed that the males were in the beginning of spermatogenesis. Males from the control group and some from the TB groups showed tubules with cysts containing spermatogonia, spermatocytes and spermatids; however, some testes of males exposed to TB showed slight to moderate interstitial fibrosis. Nevertheless, the most severely affected were males exposed to EE2 showing marked interstitial fibrosis, necrosis of germinal cells and reduced number of spermatocytes and spermatogonia in the cyst. Likewise, increased tubule number and proportionally decreased tubule diameter were observed in the testis of all EE2 exposed groups (p<0.05). Finally, a similar tubule number was observed in males exposed to EE2+20 ng l⁻¹ TB compared to control (p>0.05). This study shows that EE2 dramatically disrupts the spermatogenesis and low doses of 17β-trenbolone are unable to effectively counteract the morphological effects of EE2.