Exposure to 17α-ethynylestradiol (EE₂, 5 μg/g food) impairs some reproductive events in the protandrous gilthead seabream and a short recovery period does not allow full recovery. In this study, spermiating seabream males in the second reproductive cycle (RC) were fed a diet containing 5 or 2.5 μg EE₂/g food for 28 days and then a commercial diet without EE₂ for the remaining RC. Individuals were sampled at the end of the EE₂ treatment and then at the end of the RC and at the beginning of the third RC, 146 and 333 days after the cessation of treatment, respectively. Increased hepatic transcript levels of the gene coding for vitellogenin (vtg) and plasma levels of Vtg indicated both concentrations of EE₂ caused endocrine disruption. Modifications in the histological organization of the testis, germ cell proliferation, plasma levels of the sex steroids and pituitary expression levels of the genes coding for the gonadotropin β-subunits, fshβ and lhβ were detected. The plasma levels of Vtg and most of the reproductive parameters were restored 146 days after treatments. However, although 50% of the control fish underwent sex reversal as expected at the third RC, male-to female sex change was prevented by both EE₂ concentrations.

Endocrine-disrupting chemicals include natural and synthetic estrogens, such as 17α-ethynilestradiol (EE₂), which can affect reproduction, growth and immunity. Estrogen signalling is mediated by nuclear or membrane estrogen receptors, such as the new G-protein-coupled estrogen receptor 1 (GPER1). The present work studies the effect of EE₂ and G1 (an agonist of GPER1) on body and muscle parameters and growth-related genes of 54 two-year-old seabreams. The fish were fed a diet containing EE₂ (EE₂ group) and G1 (G1 group) for 45 days and then a diet without EE₂ or G1 for 122 days. An untreated control group was also studied. At 45 days, the shortest body length was observed in the G1 group, while 79 and 122 days after the cessation of treatments, the shortest body growth was observed in the EE₂ group. Hypertrophy of white fibers was higher in the EE₂ and G1 groups than it was in the control group, whereas the opposite was the case with respect to hyperplasia. Textural hardness showed a negative correlation with the size of white fibers. At the end of the experiment, all fish analyzed in the EE₂ group showed a predominance of the gonadal ovarian area. In addition, the highest expression of the mafbx gene (upregulated in catabolic signals) and mstn2 (myogenesis negative regulator) was found in EE₂-exposed fish.