Snakeheads Slipped a Fatal Dose

Potent Fish Toxin Nets Scores of the Alien Species in Crofton Pond

At daybreak yesterday, Maryland biologists unleashed their ultimate weapon against the strange, toothy Asian snakehead that has turned the international spotlight on a small, overgrown pond in Crofton and provided a textbook case of the dangers of alien species.

As a pair of biologists navigated a flat-bottomed boat through the shallows, focusing a stream of milky poison into the pond, the acrid scent of chemicals wafted across the water.

Fish almost immediately began to move away from the toxins, rippling and splashing the water. In the laboratory, fish exposed to the poison react within two minutes. At the pond, with cameras and reporters focused on them, biologists exhaled when distressed fish began surfacing to gulp air.

"It's a neat chemical," said Steve Early, the man in charge of the operation for the Maryland Department of Natural Resources. "It's intended to work in highly organic ponds with resistant species. It's doing exactly what we expected."

The poison, rotenone, is derived from the leaves and roots of trees and is used by some South American cultures to harvest fish from rivers and streams. Early tribal communities ground the plants into a powder and then dispersed it into the water, harvesting the fish that floated to the top.

Though generally not fatal to mammals or amphibians, rotenone is particularly deadly to fish. The poison is absorbed by the feathery surfaces of the gills, which extract oxygen from the water and shuttle it into the fish's blood.

As the poison takes effect, the fish loses its ability to transfer oxygen into its blood. Carbon dioxide builds up, and as its oxygen-starved organs begin to shut down, the fish begins to suffocate.

In a controlled setting, fish will surface within minutes, gulping for air as their lips turn pink. Within seven minutes, they will start to lose their equilibrium, fins propelling them erratically up and down through the water.

Within 30 minutes, the fish's jaws will pump a few last hopeless ounces of water across its gills, but by then its ability to absorb oxygen will be gone. Moments later, it will float to the surface, belly-up, then sink to the bottom and die.

Yesterday, even as the boat continued making passes across the pond, stirring the poison in its wake, teams of biologists began wading into the shallows with plastic buckets, scooping gasping fish from the water.

Bluegills, warmouths, crappies, chain pickerels. Into the buckets they went, their sides heaving as the oxygen drained from their bodies. Within minutes of being lifted from the water, their lungs collapse. An hour after work begins, a cry comes from a worker holding a blue pool skimmer: "I think I got one!"

Biologists inspect his find and confirm their prey: It's a snakehead. About five inches long, twice the size of the babies caught just two months ago -- and heartier and hungrier.

To prove their case against the snakeheads as notorious feeders, a biologist slits one open and lays the contents of its belly next to it: four small mosquitofish and a bluegill.

"This would be the kind of fish that would be displaced by the snakehead in the food chain," said Eric Schwaab, head of fisheries for the state.

Suddenly they are turning up everywhere. Within two hours, buckets, drink bottles and plastic bags were filled with fish.

By early afternoon, officials found what they believe started all of this: a large adult, about 18 inches long, likely one of two fish set loose in the pond nearly two years ago.

It was an honest mistake, state investigators concluded, but one that could have had enormous repercussions if the air-breathing snakeheads had slithered into the nearby Little Patuxent River.

By the end of the day, more than 150 juvenile snakeheads filled biologists' buckets, along with nearly 60 pounds of native fish. Within days, everything in the pond will be dead, officials predicted. State officials hope eventually to restock it.

Yesterday afternoon, Early took a victory lap around the pond on a four-wheel-drive utility vehicle. The snakehead saga was ending.