stocking a pond

Besides Crofton and the Potomac, the fish have popped up in several other places in the United States. In 1997, one was caught in a Southern California lake. A couple more appeared in Florida waters in 2000. In Massachusetts, one was caught in 2001 and a second in 2004. And in July 2004, an angler caught two in a lake in a Philadelphia park. Like the Crofton fish, the Philadelphia ones had settled in and started reproducing. But unlike the Crofton fish, they had access to a river—the Schuylkill, which feeds into the Delaware. Moreover, tidal gates that normally keep fish in the park had been stuck open for two years. Philadelphia fisheries managers decided that poisoning or draining the park’s interconnected ponds would cause more harm to resident fish than the snakeheads would, and have resigned themselves to snakeheads becoming a new member of the park’s ecosystem. The most recent surprise appearance was this past October when a northern snakehead was pulled out of Lake Michigan. The catch has raised fears that the voracious predator might take over the Great Lakes.

The northern snakehead, which is native to parts of China, far eastern Russia and the Korean peninsula, may seem plug-ugly to the undiscerning eye—it has big, pointy teeth and, given its particularly heavy mucus covering, a slime problem. It can grow up to five feet long. Like its reptilian namesake, it’s long and slender and can sport blotchy snakelike patterns on its skin. Unlike most fish, the northern snakehead has little sacs above its gills that function almost like lungs; the fish can surface and suck air into the sacs, then draw oxygen from the stored air as it swims. The air sacs are handy for surviving in waters that are low in oxygen, and even allow the fish to survive out of water for a couple of days, as long as it doesn’t dry out. A female lays thousands of eggs at a time, and both parents guard their offspring in a large nest they make in a clearing of aquatic plants.

Northern snakeheads are a popular food in their native range; they’re said to be good eating, particularly in watercress soup, if a bit bony. They’re fished commercially and raised in fish farms in Asia. They’ve also been sold live in markets in the United States. The Crofton snakeheads were eventually traced to a Maryland man who’d bought two of the fish in New York City for his sister to eat. When she demurred, he kept them in his aquarium and later released them. The U.S. Fish and Wildlife Service soon banned the importation and interstate transport of snakeheads, a plan that had already been in the works precisely because of fears that some snakehead species could thrive in parks, rivers and lakes if they got loose. The ban made it illegal to import all live snakehead species, including the colorful tropical species that populate the odd aquarium. Virginia has outlawed the possession of all snakeheads.