The effects of estrogens on invertebrates, fish being used as a specific example in this article, have been more pronounced than the effects on mammals. Estrogens have affected fish because they live and grow directly in contaminated waters. It would make sense that fish would have a higher 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 rapid lifespan. Additionally, because fish live directly in water, they are the largest population 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 northwest Texas. Ontario, Canada. They studied how chronic exposure to 17α-ethynyl estradiol at concentrations of 5 to 6 ng•L−1 in 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 showed that the male minnows had a high level of vitellogenin. And the vitellogenin level was higher than that observed in reference females exposed to the same conditions. Vitellogenin is a precursor protein found in egg yolks and expressed in females of 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 men 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. [Quoted March 22, 2011]23(1), 3-8. Available from: doi:10.1111/j.1439-0426.2006.00819.xTyler CR, Jobling S. 2008. Roach, sexist and gender-altering 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. Fish health effects of long-term exposure to water treatment plant effluent worn. Environmental Health Perspectives. [Cited March 22, 2011] 11481-89. Available from: doi:10.1289/ehp.8058Environmental Protection Agency. 2010. Downstream without hormones: can rabbit food solve an emerging environmental problem? [Quoted November 22, 2011] Available at: Environmental Pollution: http://www.epa.gov/ord/sciencematters/august2011/rabbitfood.htm