Vitellogenin induction in juvenile <i>Dicentrarchus labrax</i> L. treated with 17β-estradiol (E₂)-relation with exposure route and E₂ plasmatic levels

17 beta-Estradiol (E-2) is a female hormone, which has been increasingly reported as a water pollutant, and being one of the strongest estrogenic chemicals in the environment. The present study concerns 10-days exposure of immature Dicentrarchus labrax (sea bass), either water-diluted (WD, 200 or 2,000 ng/L) or intraperitoneally injected (IP, 0.5 or 5 mg/kg) E-2, in order to investigate its uptake and resulting vitellogenesis induction, measured as E-2 and vitellogenin (Vtg) plasma levels, respectively. Thus, E-2 plasma levels were significantly increased only in WD-exposure for both tested concentrations, whereas plasma Vtg increased for the highest concentrations in both experiments. These results demonstrated that both exposure routes were able to induce vitellogenesis in immature sea bass, and that an E-2-induced increase in plasma Vtg could be found without a concomitant increase in plasma levels of E-2. Based on the realistic concentrations used, these results confirm that environmental exposures to E-2 may represent an important risk, mainly to juvenile fish, namely due to the adverse consequences of an abnormal Vtg production.