Finned Pollution Is One Cost of Our Exotic Tastes

Diners in most countries are accustomed to having an international array of foods in their pantries and eateries. It started more than a millennium ago when spice traders plied the caravan routes linking China to Istanbul. From Turkey, traders shipped their condiments throughout Europe and eventually to the New World.

Northern or Chinese snakehead (Channa argus) captured in Maryland. Cait Gillespie/Maryland Department of Natural Resources
Giant snakehead (Channa micropeltes). Its sharp teeth hint at the snakehead’s carnivorous diet. Maryland Department of Natural Resources Fisheries Service
Bighead carp (Aristichthys nobilis). When allowed to range freely in rivers, bighead carp can grow to a much larger size than the one shown here. Iowa Department of Natural Resources

Most of the traders’ initial hauls—goods such as cumin, black pepper, teas, and fruits—survived long-distance travel because they were dried to resist rot and pests. More recently, global trade has permitted fresh fare (including seafood, meat, and produce) to reach dining tables half a world away within a day or two of harvesting.

But even that may not satisfy aficionados of really fresh food. They like pesto made from herbs clipped in the garden only minutes earlier or fish grilled within an hour of being pulled from the water. Catering to these desires, U.S. food purveyors now routinely import live animals or raise foreign species. However, big problems can arise if those alien species aren’t managed carefully and invade the adjacent environment. Indeed, such escapes underlie several piscine invasions that have made news in recent months.

Snakeheads

Earlier this year, news reports across the United States focused on a small pond in Crofton, Md., where an angler reeled in a strange fish. Long and slim, its protruding lower jaw contained caninelike teeth. Although it resembled native American bowfins, the fish proved to be a Chinese snakehead (Channa argus). An aggressive carnivore, this fish can grow to 4 feet in length and spend up to 3 days out of water, sometimes wriggling from one body of water to another.

Investigation traced the infestation to a local man who had purchased a pair of the fish from a live-food fish market in New York. The buyer kept his fish in an aquarium until 2 years ago, when he decided he’d had enough and dumped them into the Crofton pond where they thrived.

When Maryland wildlife officials realized that the pond supported adults and young that could overwinter, they decided to implement something like a scorched-earth policy to this aquatic environment. They poisoned the lake, killing all its finned occupants, including roughly 100 of the alien fish.

Although Crofton’s snakeheads made big news, they were hardly the first U.S. snakehead infestation. Over the past few years, wildlife specialists had detected four species of snakeheads in California, Florida, Hawaii, Maine, Massachusetts, and Rhode Island.

Though some were undoubtedly imported as part of the aquarium trade, federal officials said they suspect most of these aggressive fish entered this country as live food. These are kept in pens or tanks until a restaurant or fish market prepares them for discerning diners. The U.S. Fish and Wildlife Service has identified live snakeheads swimming in Boston and New York restaurants, where customers can scan an aquarium to select their dinner. Snakeheads can also be purchased over the Internet.

“These fish are like something from a bad horror movie,” says Gale Norton, Secretary of the Department of the Interior, under which the Fish and Wildlife Service operates. Although snakeheads, at least as adults, dine mainly on fish, many snakeheads also sample shellfish, frogs, and small reptiles — even the occasional bird or mammal. The snakehead’s hearty appetite has led some aquaculturists to employ them to clean their tanks.

Release of snakeheads into open waters, either deliberately or by accident, raises major environmental concerns. With the fish’s vagabond nature and unusual air-breathing prowess, it can spread over a broad area, even between land-locked lakes or streams.

“We simply must do everything we can to prevent them entering our waters,” argued Norton following the Crofton incident. Toward that end, on July 23, she proposed a new federal rule to prohibit the sale and transport of snakeheads in the United States.

Importers reacted by ratcheting up their trade in these fish. Whereas some 16,500 snakeheads were imported into the United States between 1997 and 2000, by this summer, 6,000 or more arrived at U.S. ports each month. Norton countered by expediting efforts to invoke the ban

The rule, which went into effect on Oct. 4, prohibits importation of live fish or eggs of any of 28 snakehead species native to lands spanning from Africa to the Asian Pacific. Violators can receive fines of $5,000 to $10,000 and prison sentences of up to 6 months.

Carp and more

However, invasive-species biologists are quick to point out that snakeheads are but one of a vast and growing set of environmentally dangerous invaders.

Many, like the infamous zebra mussels, round gobies (SN: 7/31/99, p. 68: http://www.sciencenews.org/sn_arc99/7_31_99/fob1.htm), and cholera-inducing bacteria (SN: 11/25/00, p. 348) probably entered the United States with ballast water ditched by ocean-going freighters. New moves are now afoot to begin controlling exotic species that hitchhike with ballast water (SN: 4/13/02, p. 234: available to subscribers at Stemming the Tide).

Far harder, Norton and others concede, will be policing trade in live fish. Even if ports can effectively shut the door on snakehead importers, fish already resident in the Untied States will continue to escape into the wild.

Arkansas populations of bighead carp made a spectacular escape 8 years ago. This fish now stands poised to enter the Great Lakes via an Illinois canal, according to a report in the Nov. 3. Detroit News.

Three decades ago, Arkansas’ catfish farmers imported these carp to graze algae in their catfish ponds. The carp can tip the scales at 40 to 100 pounds. But the catfish growers generally culled them, as a sideline harvest, long before they got that big. Many diners prefer the mild, pleasant taste of 6-pounders.

When a flood hit those Arkansas fish-farming ponds in 1994, it permitted many of the fast-breeding carp to escape. They reached rivers and quickly established populations in 18 states. Because even large bigheads feed on algae and plankton, when they enter new waters, they gobble the same fare that small fish eat. This can threaten the sport-fish food chain.

Currently, bighead carp can be legally imported into the United States. They are offered for sale by live-fish markets in many communities with Asian populations. Because these fish are hard to keep live in small tanks, those that aren’t sold quickly may be discarded, perhaps into local waters.

One way to evaluate the extent to which this is happening, the U.S. Fish & Wildlife Service says, is for boaters and anglers to report strange-looking fish, as the Crofton man did. The agency also asks anglers not to dump overboard any unused live bait, including minnows, because it might include species foreign to those waters.

Janet Raloff

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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