GAINESVILLE, Fla. - Few people in this country know more about the sharp-toothed Asian fish that has invaded a Crofton pond than the man some here call Dr. Snakehead.

For the past year, Walter R. Courtenay Jr. has pored through reams of papers in a trailer in the Central Florida woods to assess the risk of the snakehead to native fish species.

Today, the 68-year-old ichthyologist will join a dozen other scientists on Maryland's recently formed snakehead panel to discuss how to get rid of the fish - known for its tendency to devour other species, move on land and survive out of water for several days. It's been multiplying feverishly in a pond behind a Dunkin Donuts along Route 3, and experts worry it could get into nearby waterways.

Though Crofton is the first place that a northern snakehead has been found to have spawned in this country, Courtenay believes it won't be the last.

"Can you imagine all the things we don't know about?" he asked in an interview in his lab this week. "That's the really scary part."

Concerned about snakehead sightings in a few spots around the country, the government brought Courtenay out of retirement last fall to work on the snakehead study at the U.S. Geological Survey's Florida Caribbean Science Center. The Florida Atlantic University professor emeritus returned to a familiar and collegial lab that he had visited many times in his 40-year career.

The lab is the sort of place where scientists wear fish shirts, display fish-inspired cartoons below fish nameplates on their doors (Courtenay's is a snakehead), and send ill co-workers fish-covered get-well cards. It's not the kind of place that usually fields calls from reporters or sees its research mentioned on late night comedy shows.

Courtenay, who owns about 70 fish shirts himself, doesn't mind the attention he and the snakeheads are getting. Nor do his colleagues.

"It's good for the issue. Unfortunately it takes some sort of exotic invasion to bring this home to people," said fishery biologist Amy Benson. "I wish we didn't have these jobs, but somebody's got to look into this stuff."

Experts say Courtenay is the right person for the job.

"In North America, he's about as good as it gets," said Robert G. Howells, a fishery research biologist with the Texas Parks and Wildlife Department who worked with Courtenay when snakeheads were discovered in Houston fish markets last year.

Courtenay, who is working with two other scientists, James Williams and Leo Nico, said the snakehead study is a first for the government. "Someone realized there was a small segment of the aquarium fish trade that was selling snakeheads and some of them had been turned loose by fish owners," Courtenay said.

The report is due next month.

Last year, Courtenay and his team began e-mailing others in the "fish net" - an informal group of biologists who trade information - to see what they knew. He already knew the snakehead could survive out of water for three days, walk on its fins, and eat voraciously. But he soon learned 25 species -such as bull's eye and northern - live from the Yangtze River in China to as far north as Siberia. Many Asian cultures ascribe healing powers to the fish. Folklore has it that snakehead oil is used to prevent scarring after C-section operations.

Because it is illegal to buy a snakehead in Florida, team members searched for snakeheads in Asian markets while on vacation in Missouri and New York where they are legal. They asked colleagues to keep their eyes peeled.

They bought a bull's eye snakehead online from Rhode Island. Buster, a northern snakehead, arrived from a colleague in Boston. Williams bought Ollie, another northern snakehead, from a fish market in Orlando. The salesman, who told Williams that Ollie was a "very special catfish," recently had a not-so-friendly visit from fisheries agents.

Courtenay concluded that the northern snakehead - the species found in Crofton - was the most dangerous because it can live from the tropics to Siberia.

"We're talking cold," he said. "That fish can live anywhere it wants to in the United States."

But that point was largely academic at the time: Even though one northern snakehead had been caught in a California reservoir in 1997, and two had been caught in the St. Johns River in Orlando in 2000, the fish generally could only be found in tanks in Asian markets.

Then in June, officials from the Maryland Department of Natural Rescources e-mailed a photo of a strange fish that had been caught in the Crofton pond. Courtenay immediately identified it as a northern snakehead, confirming the fish was nesting 75 yards from the Little Patuxent River.

Officials later determined that a local man had dumped two adult snakeheads-one male and one female - into the pond two years ago after they outgrew his aquarium. Earlier this month, DNR officials captured about 100 young snakeheads. Courtenay fears thousands are lurking - merchants typically sell snakeheads when they are about two years old and at their sexual peak. Do the math, he says, and it adds up to a third generation.

But, some scientists say Maryland's fish story has been blown out of proportion.

"These stories tend to get exaggerated and take on a life of their own," said Paul Shafland, director of the Florida Fish and Wildlife Conservation Commission's nonnative fish research lab in South Florida. "You hear the fish have teeth, they breathe air. Pretty soon you hear they climb trees, they eat dogs, they tap-dance, whatever."

Shafland, who is also on the Maryland panel, said the question of the snakehead's danger is one of perspective, and that native fish are far more resilient than some think.

But the Gainesville team says the Crofton discovery bolsters their conclusions - that snakeheads are dangerous and federal law should prohibit anyone from importing them alive.

"People said, what's the probability of them ever reproducing? Well, now we know. How would two fish in 10 acres of water find each other? Well, they did," Williams said. "I can't predict today that snakeheads are going to enter every stream in the Mississippi and wreak havoc on all fish populations, but it certainly has the potential to happen."

The snakehead saga reminds Courtenay of an old fish story.

In 1967, Courtenay had just begun what would be a 30-year career teaching zoology at Florida Atlantic University when the Asian walking catfish arrived in South Florida. The working story is that it escaped from a fish farm, where a man raised it because he thought its albino color would be popular with collectors. Later, the fish farmer's brother told Courtenay it jumped out of its tanks as he drove from Miami International Airport.

Either way, the predatory fish navigated the canal system like a beltway, chomping on every fish it met. Officials soon banned them in the state, prompting farmers in Tampa to dump their collections. Tampa's fish moved south while Miami's headed north, and by the time the species met in Lake Okeechobee, Courtenay said, little could be done for the native fish.

The walking catfish hooked Courtenay on invasive species, which he's studied ever since. It also taught him an important lesson about prevention. He keeps a walking catfish paperweight on his desk as a reminder.

Courtenay has worked tirelessly on the snakehead problem - his wife, Pat, sneaked a laptop into the hospital last weekend after he was rushed to the emergency room for digestive problems. He read e-mails and news reports as he recovered.

And while he expects some belly-aching from snakehead enthusiasts for recommending a ban, he said the government should seize the opportunity to keep the willful fish from spreading.

As if to drive the point home, Courtenay reaches into the bull's eye snakehead's tank. Immediately, the asphalt-colored fish sprouts spots resembling tire tracks - a fight-or-flight reaction. Williams lowers a net, but the fish jumps out twice, pirouetting back into the water. It digs its teeth into the netting until Courtenay pulls it out.

"Here's your snakehead," Williams said. "Now, as for where it's going to go, and what it's going to do..."

"It will determine that," Courtenay interrupted. "Not us."