A comparative study on the responsiveness to 17α-ethinylestradiol (EE2) in vivo exposure in four teleost fish
Supervisor: Maren Ortiz-Zarragoitia (UPV/EHU)
Exposure to estrogenic chemicals, or xenoestrogens, discharged into the aquatic environment has been shown to induce changes in hormonal homeostasis and expression levels of reproduction-related genes (i.e. vtg and cyp19a1b) in fish, including the possibility of compromising the viability of affected populations altering the normal gametogenesis and development processes. Xenoestrogenic responses in fish vary according to the environment (freshwater vs marine), temperature and species sensitivity. One of the most potent xenoestrogens detected in the aquatic environment is the pharmaceutical 17α-ethinylestradiol (EE2), detected at ng/L in rivers and estuaries. It is used as the active ingredient in contraceptive pills and hormone replacement therapy. The aim of the present work was to study the responsiveness to EE2 exposure in four fish species. Selected species included two freshwater species (zebrafish and rainbow trout) and two marine species (European sea bass and thicklip grey mullet). To assess the estrogenic reaction after EE2 exposure well known biomarkers such as transcription levels of vitellogenin (vtg) and aromatase cyp19a1b were quantified. In order to reduce the interference of endogenous hormones, only juvenile fish were use. Fish were exposed for two days to 5 ng/L, 25 ng/L and 50 ng/L of EE2. Increased values of LSI were detected for mullets, sea bass and trout after exposure to EE2, suggesting changes on hepatic metabolic activity. Accordingly, up-regulation of vtg was detected in three out of four studied species, being vtg transcription more pronounced than cyp19a1b. Only in thicklip grey mullet cyp19a1b up-regulation was more pronounced than vtg. Results showed that the two studied freshwater species (zebrafish and rainbow trout) had higher responsiveness to EE2 than the two marine species (thicklip grey mullet and European sea bass). However, when transcription levels of target genes were compared using EE2 levels per exposed fish biomass, rainbow trout was demonstrated as the most sensitive species. This work demonstrates the species specific responses to xenoestrogens and that the contaminant per biomass load must be considered in ecotoxicological studies for a better interpretation of observed effects.