DNA Confirms It: Non-Native Catfish Are Eating At-Risk Species

Virginia Tech researchers Joe Schmitt (l) and Zach Moran (r) hold up a large blue catfish caught during their research sampling in Virginian waters. ©Jason Emmel/VT
Virginia Tech researchers Joe Schmitt (l) and Zach Moran (r) hold up a large blue catfish caught during their research sampling in Virginian waters. ©Jason Emmel/VT

By Katharine Sucher, Staff Writer

When it comes to their meals, catfish aren’t picky. And recent research from Virginia Tech confirms that non-native catfish are eating a wide range of fish species—including several species of special concern to conservationists.

A team of researchers, including Virginia Sea Grant-funded graduate student Joe Schmitt, used DNA to learn more about what non-native catfish are eating in the tributaries of the Chesapeake Bay.

In the 1970s, blue catfish and flathead catfish were introduced into the tidal rivers. Since then, researchers used diet studies to gauge how the fish affect local species. The traditional method is to examine the stomach contents, identifying the species of digested fish by looking at scales or bones.

For this study, however, the team used DNA barcoding. In this approach, specific DNA sequences in the sample are compared to those in a database to find species matches.

Prey in different stages of digestion. ©Zach Moran/VT
Prey in different stages of digestion. ©Zach Moran/VT

DNA barcoding has significant advantages over the traditional method, which often cannot identify heavily, digested fish. American shad, for example, is a species of conservation concern, but once it’s been in a catfish stomach, it can look a lot like gizzard, threadfin, or hickory shad. Telling the difference between striped bass and white perch is challenging, too.

The researchers found that DNA barcoding allowed them to confidently identify a good portion of lightly to heavily digested prey. With simple observation, the team could only identify 65% of prey items, but with DNA barcoding, 88% of prey items could be identified.

In total, researchers identified 25 fish species in the stomachs of non-native catfish, demonstrating that they eat a variety of fresh and saltwater species. Among them are several species considered of conservation concern, including American shad, alewife, blueback herring, and striped bass.

The study is the first to use DNA barcoding to research fish diets in warm water species. The research team believes that this affordable method can be useful in continuing to identify portions of the diet that were previously indistinguishable, adding to knowledge of non-native species’ impact.

The paper “Effectiveness of DNA barcoding for identifying piscine prey items in stomach contents of piscivorous catfishes” by Moran, Orth, Schmitt, Hallerman, & Aguilar can be found online at http://link.springer.com/article/10.1007/s10641-015-0448-7/fulltext.html

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