By Molly Daly

TINICUM, Pa. (CBS) — The northern snakehead, a predatory fish from China, has been caught at the John Heinz National Wildlife Refuge in Tinicum Township (Delaware County).

The fish already been found in the Schuylkill and Delaware Rivers, causing ecologists and biologists to worry about the balance of nature in our area.

Last week, we were talking about the emerald ash borer, an invasive insect (see related story).  This time it’s an invasive fish: the northern snakehead, a toothy predator with an appetite for pretty much everything that swims.

(File photo from USDA)

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Heinz Wildlife Refuge manager Gary Stolz says invasives pose the single biggest challenge to wildlife management.

“An invasive species is an exotic that’s aggressively spreading,” he explains. “What happens when you have non-native species, they don’t have natural controls. They’re not evolving with predator-prey relationships. They may throw the whole system out of balance.  It can do some serious, serious damage,” he tells KYW Newsradio.

Right now, it’s not clear what effect the snakehead will have in the region.  But Stolz says invasive colonization can go both ways.

“It’s ironic that in China, where these snakehead fish come from, they have a problem with our largemouth bass.  It’s like they’re flip-flopped on either side of the globe,” Stolz notes.