Male Fish In Mississippi Exhibit Female Characteristics

October 28, 2009

Release from: John Weiss
Post-Bulletin

LAKE CITY - Local anglers largely ignored a report that a large percentage of male largemouth and smallmouth bass in the Mississippi River in this region have female characteristics.

The Department of Natural Resources isn't all that worried either, at least not yet.

The U.S. Geological Survey reported in mid-September about 16 species of fish studied throughout the country for a decade. The most studied fish were carp and black bass (largemouth and smallmouth) because they are so widespread, said Jo Ellen Hinck, a service biologist and lead investigator for the study.

Other fish included northerns, suckers, trout and catfish. The study found that the Mississippi at Lake City had the most intersex bass -- 73 percent. The study didn't look for the cause. The condition mostly shows up with male fish having immature female egg cells in their testes, but female fish might also have male characteristics. Only remote places such as the Yukon River had no intersex fish.

DNR fisheries workers in Lake City had to field several calls from media after news of the study was released, said Kevin Stauffer, area DNR fisheries supervisor.

But calls by anglers were few, if any, he said. Most anglers don't keep any bass they catch so they aren't worried about eating them, he said. The DNR already knows that there are intersex problems because walleye and sauger males in the river near the Twin Cities were found with eggs in them several years ago, he said.

Black bass numbers are strong in the river and there is no sign they are in trouble, he said.

That could change, Stauffer said.

"This is a good wake-up call," he said.

It could mean something in the watershed is affecting fish.

Hinck said the study was to see if there were regional differences in the intersex characteristics because they can be a biological indicator of other problems. Possible causes include chemicals in the water from medications, such as estrogen from birth-control pills, or from long-lasting chemicals, such as polychlorinated biphenyls or lead, she said.

"Everything we see is underneath the microscope," she said.

The next step is to go the lab and do more precise studies, she said.

The service is a year into testing fish for problems that might come from estrogen. The next one is seeing what effect warmer water, possibly coming from global climate change, has on reproduction, she said. Fish begin spawning, in part, from temperature triggers, and maybe warmth interrupts it. The temperature study could begin next year.

Like Stauffer, Hinck said the fish could be an indicator of other problems.