In this study, zearalenone exhibited a strong concentration-dependant induction of GFP while zearalenone metabolites induced partial concentration-response, indicating that zearalenone metabolites generally behave as partial agonists of fish ERs. In agreement, zearalenone exhibited a comparably strong in vivo effect on reproduction, notably vitellogenin induction zebrafish, despite its low in vitro estrogenic potency. The phyto-estrogen genistein clearly stimulated GFP expression in RGCs in agreement with previous data. Interestingly, in tg fish genistein induced fluorescence in heart and liver, but not in brain. In this assay, industrial chemicals with known estrogenic activity, such as alkyphenolic compounds, BPA, o,p’DDT, MXC, and its estrogenic metabolite HPTE, were active, in contrast with the fact that NP had no effect in EREluc zebrafish, vtg-GFP and 5xERE:GFP. Differences were also noticed regarding the effect of BPA. In 5xERE:GFP larvae, BPA activates ER transcriptional activation only in heart and liver, whereas BPA induces GFP expression in RGCs of developing tg further confirming recent data of BPA on cyp19a1b expression in wild type zebrafish. Importantly, in mammals BPA adversely affects brain development and brain sexual differentiation. In addition to the extreme sensitivity of the cyp19a1b gene, the biotransformation capacity of the tg embryo is a clear advantage over in vitro assays. This is exemplified by MXC whose metabolites OH-MXC and HPTE directly interact with ER and potentially show long lasting additive effects. Testosterone and 17a-MT, and the non-aromatisable DHT, but not 11-KT, were able to induce cyp19a1b expression in RGCs in an ER-dependant manner. While aromatase converts androgens into estrogens that subsequently bind to ERs to activate the cyp19a1b promoter, DHT effect involves conversion into 5a-androstane-3b,17b-diol, a metabolite of DHT with known estrogenic activity. Conversion of DHT into diols requires 5areductase and 3b-hydroxysteroid dehydrogenase, both of which are expressed in the brain of developing fish and rodents. 17b-trenbolone acetate is a potent androgen extensively used in the United States as a growth promoter in beef. It is a recognized reproductive toxicant in fish. R1881 is the 17-methylated derivative of 17b-trenbolone and is also a potent non-aromatizable androgen agonist of fish and human AR. To our knowledge, this is the first report on the capacity of 17b-trenbolone and metribolone to activate an ER-dependent gene in a vertebrate. The metabolic pattern of 17b-trenbolone acetate revealed the presence of two major metabolites, 17a-trenbolone and trendione that have low affinity for androgen receptor as compared to 17btrenbolone acetate, Cycloheximide citations however their affinity towards ERs is unknown. Progesterone and 19-Nor-testosterone derivatives, used in contraception, behaved differently in tg embryos. Progesterone had no activity as expected from its lack of estrogenicity. But, we show for the first time that norethindrone and levonorgestrel, both of which are present in surface waters, were very active. In mammals, none of these compounds binds ERs, but they elicit estrogenic effects when they are metabolized into 3b, 5a-tetrahydro norethindrone or norgestrel derivatives, which are likely responsible for the observed in vivo estrogenic effects of the parent compounds.