Invasive species are the second greatest threat to biodiversity after habitat loss. Plants and animal species are introduced into new environments through many different pathways, but human actions (both intentional and unintentional) are often the cause. Some plant species, such as kudzu, are considered ornamental, and are brought in new areas and planted by humans. Other species, such as fish, are often transported as sources of food or to be kept as pets. Some species "hitch a ride" from their native lands as human-created transportation systems move cargo from one geographic location to another. People who intentionally release non-native species into new ecosystems are often unaware of the consequences that could result, but introduced species can be a grave threat to ecosystem stability.
One of the newest "foreign invaders" in the United States is the northern snakehead fish (channa argus). Native to China, Russia, and Korea, the northern snakehead was first reported in the United States in 1977, when it was found in Silverwood Lake, California (Courtenay and Williams 2002). Since that time, the invasive species has been discovered in bodies of water in states as disparate in temperature and geography as Maryland, North Carolina, Florida, and Wisconsin. The snakehead was brought to the U.S. as a food source -- the fish is considered a delicacy and reportedly, an aphrodisiac, in its native lands -- but, no one knows why the fish were released into local rivers and ponds. Unfortunately, once released, the snakehead has proven difficult to control.
Snakehead fish can be quite large, with the typical adult ranging in size between 2.5 and 5 feet, and can produce anywhere from 1,300 to 15,000 eggs per spawn multiple times a year (USGS). Their typical diet consists mostly of other fishes along with crustaceans, frogs, and small reptiles. As unbelievable as it sounds, the fish has even been known to eat small birds and mammals. The snakehead's varied and voracious appetite poses a major threat to both the smaller fish it encounters, as well as to the other fish that compete with it for food. Despite the common myth, the snakehead cannot literally walk on dry land, but it is capable of living for several days out of water as long as it is in a moist environment. The fish may leave a body of water with low oxygen levels to "wallow" on land into another body of water. This unique ability, as well as its imposing size and appetite, place the snakehead among the top predatory fish in its new habitat, and give it the potential to quickly overwhelm native species.
Despite the snakehead's slow spread across state lines, once the fish is found in a local body of water, it has proven difficult to eradicate. In places such as the Potomac River, scientists have been taken aback by the burgeoning population of snakehead fish found only a few years after introduction. States have implemented a variety of methods in an attempt to control the invasive species. In several ponds, the chemical Rotenone was applied; the application usually did kill the snakehead, but unfortunately, also most other fish in the pond. For rivers, control methods have been confined to catch and report. Some states have even offered a bounty for snakehead fish. However, due to fishermen's reports of migrating and thriving populations of the invasive species, many states are currently re-evaluating their monitoring and control policies.
Updated by Nicole Barone Callahan
InvasiveSpeciesinfo.gov: Northern Snakehead Profile
Created to connect consumers and scientists to all U.S. government information on invasive species, this website includes a profile of the Northern Snakehead fish plus a listing of related federal and state research documents, FAQ pages, photographs, and recent press releases. A comprehensive gateway site to snakehead information.
USGS: Snakeheads - A Biological Synopsis and Risk Assessment
The U.S. Geological Survey offers this comprehensive paper on the current (2004) state of knowledge regarding snakehead fish in the United States. The paper includes information on the uses of snakeheads, the risks they pose to native ecosystems, and current regulations, as well as maps and pictures of the invasive species.
USA Interactive: Mapped collection data for Channa argus
An interactive map showing the location of snakehead fish within the United States.
Maryland State Department of Natural Resources: Northern Snakehead Fish
The snakehead fish has a truly nasty looking set of teeth. Watch them go to work in this video from the Maryland State Department of Natural Resources.
Böhme, Madelaine. "Migration history of air-breathing fishes reveals Neogene atmospheric circulation patterns." Geology; May 2004; v. 32; no. 5; p. 393?396.
In this May 2004 scientific article, paleontologist Madelaine Böhme from the University of Munich uses the migratory patterns of snakehead fish to demonstrate atmospheric change. Böhme notes that "snakeheads have twice migrated from their Himalayan origins to subtropical and temperate regions in Africa and Eurasia."
Sliced Snakehead Fish and Watercress Soup
1 pound watercress
1 pound sliced snakehead fish
1 small piece dried tangerine peel, rinsed
1 slice old ginger
3 cups water
Marinade for fish:
1 teaspoon salt
1 teaspoon sugar
1 teaspoon light soy sauce
dash of pepper
1/2 teaspoon oil
1 teaspoon salt
1 teaspoon light soy sauce
Instructions: Trim off the roots of the watercress. Pluck the leaves from the stems. Use only the leafy parts. Rinse the slices of fish very quickly in cold water, drain thoroughly and marinate for 5 minutes. Bring 3 cups of water to a boil. Put in the ginger, tangerine peel and watercress leaves. Cover the pot and boil for 15 minutes over medium heat. Bring the heat to low, add seasoning, and simmer for 10 minutes. Bring the heat to high. Include the marinated fish and stir briskly. Check seasoning and serve immediately. © 2002-2005 ValueRecipes.com
Courtenay, W.R., Jr., and J.D. Williams. 2002. Snakeheads (Pisces: Channidae): A biological synopsis and risk assessment. 28 October 2002.
U.S. Geological Survey Non-indigenous Aquatic Species Program. Species Factsheet: Channa argus.