Feminized male fish abundant in American rivers

09/17/2009

Bass

A stringer of bass caught at the Blanco River in Texas' Hill Country
Copyright (c) 2006 Wendee Holtcamp

Why in the world are male fish in American rivers growing female organs? Emily Sohn reports for Discovery News, that "Intersex Fish Numbers Swell in U.S. Rivers."  Biologists with the U.S. Geological Survey just completed a study of bass in American river basins, and found many male fish have both male and female sex organs. Some species were more affected than others, and some river basins had higher levels than others, with some rivers having 70% feminization.  Wow! North and South Carolina had the highest levels, followed by the Mississippi River in Minnesota and the Yampa River in Colorado. They weren't able to link these high rates of feminization back to any particular contaminant, though.

Even though at an average site, the number of feminized male fish was low, 44% of sites had at least one feminized male. This feminization is linked to endocrine-disrupting hormones, such as those in birth control pills. The hormones end up in rivers because after we flush, the water ultimately ends up in our river basins after treatment.  The  data came over a ten year period from 1994 through 2004, when the government stopped funding the project.

In this study, black bass - including largemouth and smallmouth which are popular sportfish - seem to be most vulnerable to feminization. The question it brings to my mind is, how many other organisms besides fish are being affected by the water that these fish swim in? The New York Times recently tackled the question of why our waterways still fail to meet the objectives lawmakers set forth in 1972, when the Clean Water Act was signed into law. Their groundbreaking series, Toxic Waters, covers this issue. They created a database of water polluters that is more comprehensive than the EPAs. It's something every American should read!


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