"The water was very murky with a lot of sediment. When a fish is that large, you assume it's a carp," said Stacey Havard, a Smithsonian biologist. "An intern saw the pattern and almost instantly identified it."

The center tested the fish and reported the catch to the Department of Natural Resources and the U.S. Fish and Wildlife Service.

The toothy alien, a native of Asia, is an aggressive, rapidly breeding predator that can overwhelm habitat and push out local fish. It was first discovered in a Crofton pond in 2002 and eradicated, only to be found in Potomac River tributaries in Maryland and Virginia two years later.