|Distribution of Channa argus. Source: USGS 2004|
The northern snakehead (Channa argus) is a type of snakehead fish native to China, Russia, North Korea, and South Korea. In the United States, the fish is considered to be a highly invasive species. In a well-known incident, several were found in a pond in Crofton, Maryland in June 2002, which led to major media coverage and two movies. There have been sightings at Central Park in Burnaby, BC.
The distinguishing features of a northern snakehead include a long dorsal fin with 49-50 rays, an anal fin with 31-32 rays, a small, anteriorly depressed head, the eyes above the middle part of the upper jaw, a large mouth extending well beyond the eye, and villiform teeth in bands, with large canines on the lower jaw and palatines. It grows to a length up to 40 in (1.0 m), with one report of 60 in (1.5m), and a weight up to 17 lb 6 oz (8 kg). Its coloration is a golden tan to pale brown, with dark blotches on the sides and saddle-like blotches across the back. Blotches toward the front tend to separate between top and bottom sections, while rear blotches are more likely to be contiguous. Coloration is nearly the same between juveniles and adults, which is unusual among snakeheads, and is similar to Channa maculata, but can be distinguished by two bar-like marks on the caudal peduncle (where the tail attaches); in Channa maculata, the rear bar is usually complete, with pale bar-like areas before and after, while in Channa argus, the rear bar is irregular and blotched, with no pale areas around it.
The northern snakehead is a freshwater species and cannot tolerate salinity in excess of ten parts per thousand.  The northern snakehead is an obligate air breather; it uses a suprabranchial organ and a bifurcated ventral aorta that permits aquatic and aerial respiration.  This unusual respiratory system allows it to live outside of water for several days; it can wriggle its way to other bodies of water or survive being transported by humans. Only young of this species (not adults) may be able to move overland for short distances using wriggling motions.  The preferred habitats of this species are stagnant water with mud substrate and aquatic vegetation, or slow, muddy streams; it is primarily piscivorous, but is known to eat crustaceans, other invertebrates, and amphibians. They build spawning nests in aquatic vegetation and females discharge eggs over the nest, which are externally fertilized by males. 
Two subspecies are distinguished – C. a. argus originating from China and Korea and C. a. warpachowskii originating from eastern Russia.
As an invasive species
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In many areas of the world, the snakehead fish is considered to be an important food fish. Due to its economic value, C. argus has been introduced (intentionally or not) to several areas in the continental United States. In the US, the snakehead is a top-level predator. Introduction of C. argus poses a substantial threat to native fish populations.
The fish first appeared in US news when an alert fisherman discovered one in a Crofton, Maryland, pond in the summer of 2002. The snakehead fish was considered to be a threat to the Chesapeake Bay watershed, and wary officials took action by draining the pond in an attempt to destroy the species. The action was successful, and two adult and over 100 small fish were found and destroyed. A man admitted having released two adults, which he had purchased from a New York market, into the pond.
In 2004, 19 northern snakeheads were captured in the Potomac River, and they were later confirmed to have become established (were breeding). They are somewhat limited to that stretch of the river and its local tributaries, upstream by the Great Falls, and downstream by the salinity of Chesapeake Bay. Tests found that they are not related to northern snakeheads found in other waters in the region, alleviating some concern of their overland migration. Northern snakeheads continue to be caught in the river as of 2012.
The northern snakehead has been found in three counties of Florida, and may be established. Apparently unestablished specimens have been found in Flushing Meadows-Corona Park, New York, two ponds in Philadelphia, Pennsylvania, a pond in Massachusetts, and reservoirs in California and North Carolina. In 2008, the northern snakehead was found in drainage ditches in Arkansas, as a result of a commercial fish farming accident. It is feared that recent flooding allowed the species to spread into the nearby White River, which would allow an eventual population of the fish in the Arkansas and Mississippi Rivers.
In the summer of 2008, an infestation of the northern snakehead was confirmed in Ridgebury Lake and Catlin Creek near Ridgebury, New York. By August 2008, the New York State Department of Environmental Conservation had collected a number of the native fish, and then poisoned the waters with CFT Legumine, a liquid rotenone formulation. After the poisoning, the NYS DEC had to identify, measure, and additionally process the fish to adhere with Bureau of Fisheries procedures before disposal. The treatment plan was operated under several agents, and New York State Police were placed on stand-by in case of protests of local residents of the area.
A new concern is that this fish's spread is getting close to the Great Lakes, which it may enter and disrupt that ecosystem.
When the snakehead was found in Crofton, the piscicide rotenone was added to the three adjacent ponds. This method of containment killed all fish present in the water body to prevent the spread of the highly invasive snakehead. The chemical breaks down rapidly, and has a half-life in water of one to three days.
On June 1, 2013, Caleb Newton of Spotsylvania County, Virginia, caught a 17-pound, 6-ounce northern snakehead which was officially listed as the biggest ever caught, according to the International Game Fish Association. 
In popular culture
They are respected among some Chinese fishermen for their virtue. Parent fishes are known to sacrifice themselves to protect their young. It is said that the young fishes rush to feed upon their mother after their mother gives birth and is temporarily unable to catch prey.
- Courtenay, Jr., Walter R. and James D. Williams. Chiana Argus USGS Circular 1251: Snakeheads (Pisces, Chinnidae) - A Biological Synopsis and Risk Assessment. U.S. Department of the Interior, U.S. Geological Survey. 2004-04-01. Retrieved 2007-07-15.
- (Hogan, 2012)
- http://www.foxnews.com/science/2013/08/07/huge-frankenfish-hooked-in-virginia-sets-world-record/?intcmp=trending http://www.washingtonpost.com/local/confirmed-monster-northern-snakehead-snagged-in-virginia-a-world-record/2013/08/07/e38722d8-ff92-11e2-8294-0ee5075b840d_story.html
- (Courtenay and Williams 2004).
- (Ishimatsu and Itazaw 1981, Graham 1997).
- (Courtenay and Williams 2004).
- (Okada 1960).
- (Okada 1960).
- Fields, Helen (February 2005). "Invasion of the Snakeheads". Smithsonian Magazine. Retrieved 2008-03-07.
- Potomac snakeheads not related to others Baltimore Sun, 2007-04-27.
- Orrell, Thomas M. and Lee Weigt The Northern Snakehead Channa argus (Anabantomorpha: Channidae), a non-indigenous fish species in the Potomac River, U.S.A.. Proceedings of the Biological Society of Washington, 118(2):407–415. 2005. Retrieved on 2007-07-16.
- Fahrenthold, David A. Potomac Fever Washington Post, Page W12, 2007-07-08. Retrieved on 2007-07-16.
- "Rotenone". Pesticides News 54: 20–21. 2001.
- Material Fact Sheets - Rotenone Resource Guide for Organic and Disease Management. Cornell University. Retrieved on 2007-07-16.
-  B.C. to consider ban on sale of ‘Frankenfish’ after reported sighting in Burnaby pond - Canadian Press/National Post
- "Eating the killer Snakehead out of existence". BBC News. 2013-09-03. Unknown parameter
- "‘Frankenfish’ catch earns Virginia man a world record". Washington Times. Retrieved 8 August 2013.
- http://hamptonroads.com/2013/08/17pound-6ounce-frankenfish-va-world-record 17 pound - 6 ounce "Frankenfish" in VA is World Record (Virginian Pilot, August 7, 2013)
- "Channa argus". Integrated Taxonomic Information System. Retrieved 24 January 2006.
- Froese, Rainer and Pauly, Daniel, eds. (2005). "Channa argus" in FishBase. 10 2005 version.
- Anonymous. 2005. 2005 World Record Game Fishes. International Game Fish Association, Dania Beach, FL. 400 pp.
- Courtenay W. R. Jr., and J. D. Williams. 2004. "Snakeheads (Pisces, Channidae).—A Biological Synopsis and Risk Assessment", U.S. Geological Survey Circular 1251, vi+143 pp.
- Hogan, C.Michael. 2012. Northern Snakehead. Encyclopedia of Earth. Eds. E.Monosson & C.Cleveland. National Council for Science and the Environment. Washington DC.
- Ishimatsu, A., and Y. Itazaw. 1981. "Ventilation of the air-breathing organ in the snakehead Channa argus."—Japanese Journal of Ichthyology 28(3): 276–282.
- Graham, J. B. 1997. Air-breathing fishes: evolution, diversity, and adaptation. Academic Press, San Diego, California, xi + 299 pp
- Okada, Y. 1960. "Studies of the freshwater fishes of Japan, II, Special part".—Journal of the Faculty of Fisheries Prefectural University of Mie 4(3): 1–860.
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