Saturday, January 28th, 2023
Saturday, January 28th, 2023

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Blue cats appear to have taste for adult Asian carp

Springfield — As it turns out, blue catfish in Illinois have an appetite for adult silver carp. White bass and gar prefer younger versions of Asian carp species.

And nearly all of the state’s native fish species will feed on the carp if given the opportunity.

How do we know this?

Researchers and graduate students from Western Illinois University spent a great deal of time and effort studying the diets  of fish to determine their taste for Asian carp, an invasive species that has fisheries biologists and Lake Michigan sportsmen nervous.

Working out of the Illinois River Biological Station at Havana, WIU – in collaboration with the U.S. Geological Survey, the Illinois Natural History Survey, and the Upper Midwest Environmental Sciences Center – found that native fish species do indeed prey heavily on juvenile Asian carp.

The finding may be useful to the defense against carp, but because the fish tend to prefer small carp, the speed at which Asian carp mature could limit its effectiveness.

Those looking at fish diets used techniques like electrofishing and stomach content analysis to figure out how native fish there interact with young Asian carp.

Cory Anderson, a research assistant in the Department of Biological Sciences at WIU, who conducted the work alongside graduate student Rebekah Haun, presented results of diet studies this winter at the Midwest Fish and Wildlife Conference in Indianapolis.

According to Anderson, stomach contents from 1,500 native predatory fish caught in the Illinois River’s LaGrange Reach in 2014 were examined. Asian carp were found in the stomachs of channel catfish, flathead catfish, largemouth bass, white bass, black crappies, white crappies, and gar species.

Anderson noted that small Asian carp were extremely abundant following a large spawning event in the summer of 2014.

“When any food source is abundant we expect that predators will take advantage, but some predators were actually going out of their way to select Asian carp,” he explained. “Gar were particularly fond of Asian carp, which accounted for half of all fish found in gar stomachs.  White bass were also selectively preying on small carp and had a high abundance of them in their stomachs.”

The research team knew that one limitation of native predator fish is that most are unable to eat adult Asian carp – it takes a fish with a very big mouth to swallow a 20-30 inch long carp. 

To that end, WIU grad students Tad Locher and James Lamer searched for a scenario where a large predatory fish might feed successfully on adult silver carp.

They struck gold in a backwater of the Mississippi River near Alton.

Blue catfish, which can top out at over 100 pounds, are opportunistic predators but often roam open water in search of shad and other baitfish. In the Alton backwater, blue catfish were finding lots of silver carp, according to Locher and Lamer. Their research contribution showed that stomach contents from 68 blue catfish included many larger Asian carp.

The average age of silver carp eaten by blue catfish was 3.9 years.

Other top predators like muskies might also have the ability to prey on mature Asian carp.

Anderson said that scientists considered all the predatory native fish they could get their hands on, including white bass, largemouth bass, shortnose gar, flathead catfish, and crappies. 

“It was easy to see if a fish had eaten a young carp, because carp have pharyngeal teeth,” Anderson said. “Regardless of the carp species, they all develop these teeth at a young age and carry them through to adulthood. When a juvenile Asian carp is eaten by another fish, researchers found that these teeth were the last things to digest.”

Researchers also took DNA samples to identify the exact species of Asian carp that were eaten.

“We’re actually still waiting on that,” Anderson said. “We were able to use the teeth of Asian carp, pharyngeal teeth, because the juveniles look so much like the adults.”

White bass, which were evaluated throughout a year, fed heavily on juvenile Asian carp. About half of all the white bass sampled had Asian carp in their stomachs. More than 60 percent of gar were found to have eaten carp.

“We’re not sure about the white bass, but the gar – they’re a surface level feeder,” Anderson said. “It seems like their feeding style worked for the carp.”

Channel catfish were also found to eat a lot of the young carp. Thirty-nine percent of catfish had eaten at least one, Anderson said.

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