Estrogen effects on invertebrates, fish being a specific example in this article, were more pronounced than the effects on mammals. Estrogens affected fish because they live and develop directly in contaminated waters. It would make sense that fish would have a more severe rate of feminization in a natural environment, and that if estrogen concentrations became too high, land animals would begin to show feminization in the wild. Many types of fish are ideal for experiments on the effect of estrogen because they have a short lifespan. Furthermore, since fish live directly in water, they are the population most affected by estrogen. Researchers Kidd, Blanchfield, Mills, Palace, Evans, Lazorchak, and Flick (2007) conducted a 7-year whole-lake experiment in the Experimental Lakes Area (ELA) in northwestern Ontario, Canada. They studied how chronic exposure to 17α-ethinyl estradiol at concentrations of 5–6 ng•L−1 of the fathead minnow (Pimephales promela) would affect the minnow. Over the 7 years they checked the minnows periodically, after 7 weeks and after 3 years and so on, and the results were that the male minnows had an elevated level of vitellogenin. And the level of vitellogenin was higher than that observed in reference females exposed to the same conditions. Vitellogenin is a precursor protein found in egg yolks expressed in female fish species and most invertebrates. The presence of vitellogenin in males is a form of feminization because if enough estrogen is present the Vg gene will be expressed. Vg gene expression is induced by estrogen-dependent activity, and in normal males estrogen levels are too low to induce vitellogenesis. Vg gene expression can also be used as a molecular marker for...... middle of paper ......eminization. Journal of Applied Ichthyology. [Cited March 22, 2011]23(1), 3-8. Available from: doi:10.1111/j.1439-0426.2006.00819.xTyler CR, Jobling S. 2008. Roach, Sex, and Gender-Bending Chemicals: The Feminization of Wild Fish in English Rivers. BioScience.[Cited March 22, 2011] 58(11), 1051-1059. Available from: doi:10.1641/B581108Liney KE, Hagger JA, Tyler CR, Depledge MH, Galloway TS, Jobling S. 2006. Health effects in fish of long-term exposure to wastewater treatment plant effluent. Environmental health perspectives. [Cited March 22, 2011] 11481-89. Available from: doi:10.1289/ehp.8058Environmental Protection Agency. 2010. Hormone-Free Downstream: Can Rabbit Food Solve an Emerging Environmental Problem? [Cited November 22, 2011] Available from: Environmental Pollution: http://www.epa.gov/ord/sciencematters/august2011/rabbitfood.htm