In River of Many Aliens, Snakehead Looms as Threat

Nonnative species, many of them brought in for the benefit of anglers, are so prevalent that a Potomac snakehead might swim through thickets of such Asian plants as hydrilla and Eurasian watermilfoil. They might go past thousands of Corbicula clams, also from Asia, which first appeared in the river about 1980.

The Potomac's bass and carp were put there in the 19th century. Other aliens are clearly former aquarium fish, such as the goldfish and the piranha. (A piranha, by the way, does not fare well against a mid-Atlantic winter.)

In other cases, mysteries persist. How to explain that the blue catfish can grow several feet long in the Potomac? The clear presumption is that they didn't get to this area on their own.

Among some scientists, the concern over the snakehead is on behalf of the river's native species. American shad, for instance, could be hurt if snakeheads gobble up baby fish migrating downstream.

Yet in an irony of modern environmentalism, much of the concern is about what the snakehead will do to a previous invader: largemouth bass.

Like the snakeheads, the bass are ambush predators, lurking under plants or below docks and snapping up prey as it passes.

If the snakehead displaced them, it would ruin a fishing industry that brings hundreds of anglers and millions of dollars to the region annually.

"It's really on the minds of the bass fisherman now," said Steve Chaconas, a bass-fishing guide based in Alexandria.

For now, however, the bass population doesn't seem to have changed. So scientists are left with few solid conclusions about the snakehead's potential.

On Thursday, two Virginia state biologists motored into a creek off the Potomac, steering what amounted to a gigantic fish taser. They turned on the juice. Their "electrofishing" boat sent 1,061 volts into the water through an array of wires, and twitching fish began floating to the surface.

Their catch provided a quick lesson in the Potomac's recent history, in which human experiments and mistakes have turned the river into a kind of open-water aquarium. Up popped largemouth bass, common carp, a couple of goldfish.

But the biologists were looking for something else.

"I think I saw one, John," said Steve Owens at one point, calling to his partner from the bow of their flat-bottomed boat.

The boat surged, and Owens stabbed his dip net into the water. He came up holding a mottled-green monster, with a mouth big enough to fit around a soft-drink can.

"There's a snakehead!" said his partner, John Odenkirk of the Virginia Department of Game and Inland Fisheries.

Later in the day, Owens and Odenkirk stood on a dock and measured the two snakeheads they caught. The crew of a Fairfax County fireboat walked over and marveled at the fish, each nearly two feet long.

"It's another mouth to feed," Owens said to them.