An adult northern snakehead was discovered last Thursday by scientists in a river just south of Annapolis, Maryland. The mature, egg-bearing fish is raising the possibility that low salinity in the Chesapeake Bay may have allowed the invasive snakehead to escape from the nearby Potomac River.

The two-foot-long snakehead, sometimes known as fishzilla is a toothy alien, native to Asia and Africa. The notoriously invasive species has become a byword for monster in popular culture. The fishzilla can actually live for a few days out of water, thanks to air chambers that function as primitive lungs.

The snakehead became a national news topic back in 2002 when a group of them were found spawning in a Crofton, Maryland pond. They were eradicated, but by 2004, they were found to be permanently established in the Potomac River. An aggressive, rapidly breeding predator, snakeheads can overwhelm habitat and push out local fish.

Northern snakeheads are established in Pennsylvania and New York, and small numbers have been caught in California, Florida, Massachusetts and North Carolina. Meanwhile, Maryland and Virginia biologists continue to track them with radio telemetry and electrofishing to figure out population densities.

Snakeheads have become so abundant in the Potomac that the state of Maryland Department of Natural Resources is trying to get chefs to cook them and sell them in restaurants.

Last Thursday's discovery by biologists from the Smithsonian Environmental Research center occurred as the group took their annual fish samples by net.

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. They were particularly concerned that it was an egg-bearing female.