Monday, September 28, 2015

What Does a 100 lb Catfish Eat?

SERC intern womanhandling a Blue Catfish
Answer, anything it wants: DNA solves puzzle of catfish dinners
DNA analysis is proving to be a valuable tool for scientists trying to gauge the environmental impact that invasive blue catfish (Ictalurus furcatus) and flathead catfish (Pylodictis olivaris) are having on native populations of fish in eastern Virginia waterways. Both species are strong predators native to the Midwest and western North America; flathead catfish were introduced to the rivers of Virginia in 1965 and blue catfish from 1975 through the 1980s.

By studying the stomach contents of blue and flathead catfish caught in the waterways of tidewater Virginia, biologists are piecing together just which native Virginia fish species these invasive catfish are eating. Sifting through partially digested earbones, spines and scales, the researchers using only their expertise in fish morphology, can identify 65 percent of the species found in catfish stomachs. However, the rest of the material—25 to 30 percent of the stomach contents—often consists of heavily digested, indistinguishable remains.
Ah, yes, sifting through fish vomit; a classic intern  job. But what happens when we have a machine that identifies the fish in the glop? Do interns become unnecessary?
“You may get a chunk of flesh on a bit of spine, and you know it was a fish, but not what [fish] it was,” explains Robert Aguilar, a biologist at the Smithsonian’s Environmental Research Center (SERC) and co-author of a recent paper in the journal Environmental Biology of Fishes.

Enter DNA barcoding. By taking 10- to 25-milligram samples of the unidentified remains and subjecting them to DNA amplification and sequencing, the scientists increased the identification rate to 88 percent of fish prey
items overall. DNA recovered in catfish stomach contents is matched to a global genetic barcode library of species, which includes many samples collected in the Chesapeake Bay. The growing database includes fish, shellfish, insects and plants.
In other words, just about anything it encounters with enough calories to make it worth the trouble.
“Many of the highly digested samples were identified as species of conservation and management concern,” the scientists report, “including striped bass and white perch or American shad, alewife and blueback herring…” Their results show the catfish eat a varied fish diet.
I can't imagine that they really thought that the big cats would turn up their noses at the endangered fish that wander past their whiskers. It's not like they have signs identifying them, They probably don't even know (or care) what it is until it's past their gullet and into their stomach.

Wombat-socho has the big list "Rule 5 Sunday: Time For The Professionals", ready at The Other McCain.


  1. Replies
    1. I don't think anyone knows, or will admit it. Probably fisherman, trying to get bigger catfish established. I don't know of a waterway that connects the Mississippi drainage, where they came from, to the Potomac, although the are pretty close up in the Appalachians.