Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
Biologists Discover Intersex Fish More Widespread
Northeast Region, April 22, 2009
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Smallmouth bass study map
Smallmouth bass study map - Photo Credit: n/a
 Sampling for smallmouth bass in Conococheague Creek, MD. USFWS
Sampling for smallmouth bass in Conococheague Creek, MD. USFWS - Photo Credit: n/a

A recent study of intersex abnormalities in fish conducted by researchers from the Chesapeake Bay Field Office and the U.S. Geological Survey in the Potomac River watershed showed that at least 82 percent of male smallmouth bass and in 23% of the largemouth bass had immature female germ cells (oocytes) in their reproductive organs.


This condition, a type of intersex, is a disturbance in the fish's hormonal system and is an indicator of exposure to estrogens or chemicals that mimic the activity of natural hormones. Several other abnormalities were also noted, some affecting female bass.


In addition to sampling fish, scientists collected water samples at fish collection sites to try to identify what was causing these abnormalities. One possible source of the abnormalities was the discharge coming out of wastewater treatment plants.


Two scientific papers will be published in the May 2009 issue of Environmental Toxicology and Chemistry. Based on the results of these studies, no single chemical or source could be identified as causing the intersex abnormalities.  Scientists pointed out that multiple chemicals, not solely associated with agriculture or wastewater treatment plant effluents, may be responsible.  


To read a factsheet on this issue go to: www.fws.gov/chesapeakebay

To view a Washington Post article on this subject see: www.washingtonpost.com/wp-dyn/content/article/2009/04/21/AR2009042103460.html


For more Information contact:

Fred Pinkney




Contact Info: Kathryn Reshetiloff, 410-573-4582, kathryn_reshetiloff@fws.gov
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