It sounds like a critter from a cheap science fiction movie, a companion for the Creature from the Black Lagoon.

But this fish is real and it's living in a pond in Crofton.

A northern snakehead, usually found in the Yangtze River region of China, was hooked by an angler last month in the pond behind the Dunkin Donuts on Route 3.

Torpedo-shaped and aggressive, snakeheads lurk in the deep and gobble up every other fish in sight.

They can grow to be 18 inches long, live three days out of water and, if the need arises, walk short distances on their extended fins.

"This is one tough customer," said Bob Lunsford, a biologist with the Department of Natural Resources. "If I had to be a fish, this is the fish I'd be."

Scientists are worried that with its unusual mobility and survival instincts, a snakehead could negotiate the 75 yards from the pond to the Little Patuxent River, where it could eat its way downstream to the Jug Bay Wetlands Sanctuary.

State biologists have been advised by experts to take action, and they are pondering their options.

Yesterday, they used canoes to set traps in the 9-acre gravel pit pond, a popular spot for catching smallmouth bass and bluegills.

The biologists also shored up the area between the edge of the pond and river with sandbags in the event a heavy storm or remnants of a hurricane cause the river to overflow its banks and help the snakehead escape.

Especially worrisome is that they don't know how many snakeheads are in the pond.

"The presumption is we're dealing with a small number," said Eric Schwaab, the head of DNR fisheries. "But we want to make sure we get all of them. Controlling this could be a costly undertaking."

There's at least one; the angler who caught it snapped three photos and tossed it back into the pond.

But, his curiosity piqued, he went to Annapolis June 14, pictures in hand, to see whether the DNR could put a name to his catch.

A flurry of e-mails between state biologists and experts at the U.S. Geological Survey in Florida led to the unpleasant conclusion Tuesday that Crofton had a problem.

Normally, the DNR would consider the discovery of a snakehead in Maryland an oddity, a fish tossed away by an unsuspecting aquarium owner who had grown tired of waking up each day to find only one thing swimming in the tank.

Single snakeheads have been documented in Maryland about a half-dozen times.

But a discovery Wednesday gave biologists pause.

"There was a pet shop in a nearby strip mall that went bankrupt," said Lunsford. "That heightens our concerns somewhat that more than one fish could have been dumped."

A breeding population would greatly magnify the problem, and snakeheads can survive and reproduce quite nicely in Maryland's climate.

Lunsford said if they begin seeing other hardy tropical fish in the pond, they'll quickly intensify their efforts to eliminate the snakeheads.

Walter Courtenay, a researcher at the USGS Florida Caribbean Science Center, said snakeheads have been caught in Florida, Massachusetts and California. Their origin is not known.

"Of the 28 recognized species of snakeheads, this species has the capability to become established throughout most of the United States and southern Canada," he said in an e-mail.

"Frankly, it wouldn't surprise me that they might be reproducing there [in Crofton], although I would hope the individual that was caught is the only snakehead in that pond."

Scientists say there is another reason to fear there's more than one snakehead down there.

Asian specialty markets often carry the fish as a delicacy, but because it is banned in many places and interstate shipment is restricted by federal law, merchants sometimes surreptitiously dump them.

At its deepest, the pond is estimated to be 5 to 9 feet. Poisoning the snakehead is not an option because that would kill all the fish and create the potential for dangerous runoff.

Draining the pond might be futile because a snakehead can live for months burrowed in the mud.

Vegetation around the pond makes it difficult to bring in the boat with the equipment to put an electric charge in the water and bring stunned fish to the surface.

Biologists could spray the weeds with herbicide, "but that would lower the oxygen level and it could run away," Lunsford said.

"We don't want to run him out" and lose track of the fish, he said.

So Schwaab and Lunsford will fall back on an angler's No. 1 virtue -- patience -- waiting until fall when the vegetation dies naturally.

In the meantime, the state will tack up "Wanted" posters around the pond, warning anglers not to practice catch-and-release with snakeheads, to kill one if they catch it and then call the DNR.