Northern snakehead
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Order: Perciformes
Family: Channidae

[Photo] Northern snakehead (Channa argus) from USGS (http://cars.er.usgs.gov/pics/snakehead/snakehead.html). Date: 18 June 2003.

The northern snakehead (Channa argus) is a fish native to China, Russia, and Korea. In the United States, the fish is considered to be a highly invasive species.

Biology
Distinguishing features of the northern snakehead include a long dorsal fin with 49-50 rays, anal fin with 31-32 rays, small anteriorly-depressed head, eye above the middle part of the upper jaw, large mouth extending well beyond the eye, villiform teeth in bands, large canine on the lower jaw and palatines (see Fish Anatomy: Teeth), length up to 40 inches (1.0 m), with one report of 60 inches (1.5m), and weight up to 15 pounds (7 kg). 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. Coloration 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 (Courtenay and Williams 2004). The northern snakehead is an obligate air breather; it utilizes a suprabranchial organ and a bifurcate ventral aorta that permits aquatic and aerial respiration (Ishimatsu and Itazaw 1981, Graham 1997). This unusual respiratory system allows it to live outside of water for several days, where concern is that it might wriggle its way to other bodies of water or be transported by humans. Note that only young of this species (not adults) may be able to move overland for short distances using wriggling motions (Courtenay and Williams 2004). 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 (Okada 1960). The northern snakehead is capable of spawning more than once in a breeding season (Courtenay and Williams 2004). They build spawning nests in aquatic vegetation and females discharge eggs over the nest, which are externally fertilized by males (Okada 1960).

Channa argus as an invasive species
In many areas of the world, the snakehead fish is considered to be an important food fish. Due to its economic value, Channa argus has been introduced (intentionally or not) to several areas in the continental United States. In the U.S., the snakehead is a top-level predator. Introduction of Channa argus poses a substantial threat to native fish populations.

The fish first appeared in U.S. news when an alert fisherman discovered one in a Crofton, Maryland, pond in the summer of 2000. 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 in the pond he had purchased from a New York market.

In 2004, nineteen northern snakehead were captured in the Potomac River, and it is was later confirmed that they had 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 snakehead continue to be caught in the river as of 2007.

The northern snakehead has been found in three counties of Florida, and may be established. Apparently non-established specimens have been found in Flushing Meadows-Corona Park, New York, two ponds outside Philadelphia, Pennsylvania a pond in Massachusetts, and reservoirs in California and North Carolina.

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.

http://en.wikipedia.org/wiki/Northern_snakehead

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