Why Are These Male Fish Growing Eggs?

Feb 6, 2016

Photo credit: Joel Sartore

By Lindsey Konkel

Silver maples, lanky and bare, stand on the frozen flood plain at the Missisquoi National Wildlife Refuge. Two sets of tracks—fox and mouse—weave across the snowy surface of the river, which is home to bass, muskrats, and beavers. In the fall, more than 20,000 migrating ducks will converge here, and in the summer, one of the refuge’s rarest species, spiny softshell turtles, will bask and forage on its gravelly beaches and sandbars.

Sixty miles south of Montreal, near the U.S.-Canada border, Missisquoi National Wildlife Refuge is one of the most productive and pristine wetland ecosystems in the Northeast. Yet even here, scientists have found an abundance of fish with bizarre abnormalities that suggest exposure to hormone-disrupting water pollution.

Scientists from the U.S. Fish and Wildlife Service and the U.S. Geological Survey studied fish in 19 national wildlife refuges in the U.S. Northeast, including Missisquoi. Their conclusion: An astonishing 60 to 100 percent of all the male smallmouth bass they examined had female egg cells growing in their testes.

Scientists call this condition intersex, and while its exact causes are unknown, it’s been linked to manmade, environmental chemicals that mimic or block sex hormones.


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One comment on “Why Are These Male Fish Growing Eggs?”

  • @OP – Scientists call this condition intersex, and while its exact causes are unknown, it’s been linked to manmade, environmental chemicals that mimic or block sex hormones.

    Hormone pollution and synthetic chemicals which mimic hormones are widespread industrial and waste-site, contaminants of air and water in some areas.
    While these pollutants can affect any vertebrate organisms, some fish are particularly sensitive, being immersed in the polluted water, and some fish, can in any case, change their sex within their life time.



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