Tracking Asian carp by what they leave behind

Oct 24, 2013

There’s a lot of time, money and effort being spent to keep Asian carp out of the Great Lakes.

To keep them out, we first have to know where the carp are.

Biologists often go out and sample water from rivers and lakes to look for carp. They test the water for genetic material, and some of those tests have turned up positive for Asian carp.

Last year, 20 samples turned up positive hits in Lake Erie. The positive DNA hits raise alarm bells that an invasive carp species might be establishing a population in the Great Lakes.

But the presence of carp DNA does not mean an actual fish was swimming in that area.

The genetic material could have come from somewhere else, like a bird that eats fish, or from a boat that was once in water where the carp are found.

Researchers are looking for better ways to track whether an actual carp is in a particular area.

One clue that might help them is fish poop.

Wen-Tso Liu, a Civil and Environmental Engineering Professor at the University of Illinois at Urbana-Champaign, says “microbial source tracking” has proven successful in other areas.

"In the last decade, the use of this microbial source tracking has been successfully applied to identify sources of fecal contamination in rivers, lakes and even drinking water distribution systems," said Liu.

"So we think we can apply exactly the same concept to this monitoring of the Asian carp population."

The communities of microbes in fish guts can be unique. And there are plenty of samples to be found.

From their press release:

Since fish feces are plentiful in waterways, monitoring could be easier than with techniques that have focused on detecting the DNA of the targeted species in sloughed-off skin tissue, Liu says.

If researchers can corroborate their DNA findings with microbial findings, they can be more certain than a particular fish was in a certain area.

Mark P. Gaikowski is a Supervisory Biologist with the U.S. Geological Survey’s Upper Midwest Environmental Sciences Center.

He’s working to identify what is unique about Asian carp poop.

“You take out the digestive tract in a very careful manner, so you don’t contaminate the samples from one fish to another fish, and you collect the internal scrapings of that fish’s digestive tract.”

Tests in the lab are ongoing and Gaikowski says they have to be careful to make sure the technique works before they use it in the field.

*This post has been updated.