|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 Europe, the first report of the species was from Czechoslovakia (now the Czech Republic) in 1956. 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. Sightings have been reported 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 (1.5 m), and a weight up to 17.49 lb(7.33 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 C. maculata, the rear bar is usually complete, with pale bar-like areas before and after, while in C. 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 million. It 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.
The northern snakehead can double its population in a minimum of 15 months. It reaches sexual maturity at age two or three, at which time it will be about 30 to 35 cm long. The eggs are fertilized externally; a female can lay 100,000 eggs a year. Fertilization occurs in shallow water in the early morning. The eggs are yellow and spherical, about 2 mm in diameter. Eggs hatch after about 1-2 days, but they can take much longer if the temperature is very low. The eggs are guarded by the parents until yolk absorption, when the eggs are about 8 mm long. 
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; its introduction 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 adults 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 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. Recent flooding may have 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 a liquid rotenone formulation. After the poisoning, the NYSDEC 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.
In April 2013, sightings of the species in New York Central Park's Harlem Meer have prompted city officials to urge anglers to report and capture any individuals. Ron P. Swegman, author of several angling essays on Central Park's ponds, confirmed the species had put both anglers and the New York State DEP on high alert.
As of late 2013, authorities in Virginia and Maryland are counting snakeheads in the Chesapeake Bay to better understand the impact of the introduction of the fish to the local ecosystem. Virginia has criminalized the "introduc[tion]" of snakeheads into the state without specific authorization, although the relevant statute does not explain whether mere importation is sufficient to constitute "introduc[tion] into the Commonwealth" or whether instead release into the environment is required.
On May 20, 2014, Luis Aragon of Triangle, Virginia, caught a 17-pound, 12-ounce northern snakehead which was officially listed as the biggest ever caught on rod and reel, according to the International Game Fish Association. On May 20, 2016, Emory "Dutch" Baldwin of Indian Head, Maryland boated an 18.42 pound northern snakehead in tidal marshes of the Potomac using archery tackle. This fish is listed as the state sport record in Maryland by the Department of Natural Resources and likely world record holder. 
In traditional culture
They are respected among some Chinese fishermen for their virtue, as parent fishes are known to sacrifice themselves to protect their young. The young fish are said to 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)
- "Maryland Man Sets State Record For Biggest Snakehead Caught". wbal.com. Retrieved 2015-10-23.
- (Courtenay and Williams 2004).
- (Ishimatsu and Itazaw 1981, Graham 1997).
- (Okada 1960).
- "Issg Database: Ecology of Channa Argus." Issg Database: Ecology of Channa Argus. N.p., 21 May 2009. Web. 26 Mar. 2016.
- 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
- http://observer.com/2013/05/gone-fishin-casting-for-invasive-species-in-central-park/the noted
- Strahan, Tracie (2013-04-30). "Invasive predator fish that can live out of water for days to be hunted in Central Park". NBC News. Retrieved 2013-12-09.
- "Snakehead fish: Can invasive species be eaten out of existence?". BBC News. 2013-09-03. Retrieved 2013-12-09.
- Code of Virginia § 18.2-313.2: "Any person who knowingly introduces into the Commonwealth any snakehead fish of the family Channidae[...] without a permit from the Director of Game and Inland Fisheries [...] is guilty of a Class 1 misdemeanor [punishable by up to twelve months in jail and/or a fine of up to $2,500]."
- "IGFA World Record".
- "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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