Amur snakehead, eastern snakehead, ocellated snakehead, snakehead, Ophicephalus argus Cantor, 1842; Ophiocephalus argus kimurai Shih, 1936; Ophicephalus argus warpachowskii Berg, 1909; Ophicephalus pekinensis Basilewsky, 1855.  Courtenay and Williams (2004) provide a larger list, including names used in other languages.

Snakeheads (family Channidae) are morphologically similar to the North American native Bowfin (Amia calva), and the two are often misidentified. Snakeheads can be distinguished from Bowfin by the position of pelvic fins (directly behind pectoral fins in snakeheads, farther back on body in Bowfin) and the size of the anal fin (elongate and similar in size to dorsal fin in snakeheads, short and much smaller than dorsal fin in Bowfin). Additionally, Bowfin can be identified by the presence of a bony plate between the lower jaws (gular plate) and a distinctive method of swimming through undulation of the dorsal fin. The Northern Snakehead is also very similar to the Burbot (Lota lota), another North American native fish species.

In its native range, reproductive maturity is typically reached when fish are 2-3 years old (Dukravets and Machulin 1978), but may occur only after one year of growth in some introduced populations (USACE 2011). In the U.S., northern snakehead spawning has been observed to start by the end of April, peak in June, and continue through August (Gascho et al. 2011). Adult females build circular floating nests from clipped aquatic plants and release their pelagic, nonadhesive, buoyant eggs on top (Landis and Lapointe 2010). Each spawn can consist of 1300-1500 bright orange-yellow eggs (about 1.8 mm diameter), with up to five spawns occurring within a year. Northern snakehead fecundity can range from 22,000-51,000 in its native range (Amur basin; Nikol'skiy 1956) to 28,600-115,000 in an introduced population (Syr Dar'ya basin, Turkmenistan/Uzbekistan; Dukravets and Machulin 1978). Both parents guard the nest of eggs from predation and continue to guard the hatched fry for several additional weeks (Courtenay and Williams 2004, Landis and Lapointe 2010). Depending on water temperature, eggs may hatch in fewer than three days (28 hours at 31°C, 45 hours at 25°C, and 120 hours at 18°C; Landis and Lapointe 2010). Larvae experience rapid growth after their first two weeks, though overall individual growth rate in North American populations appears to be less than that in both native and introduced Asian populations (Landis et al. 2011).

Fry initially feed on zooplankton, before moving on to a diet of small insects and crustaceans (e.g., cladocerans, copepods, small chironimid larvae). Juveniles may feed on small fish, including goldfish (Carassius spp.) and roach (Rutilis spp.; Courtenay and Williams 2004). As an adult, the northern snakehead is a voracious feeder (Okada 1960), and its diet may include fish up to 33 percent of its body length (Courtenay and Williams 2004).  Adult prey items include loach (Cobitis spp.), bream (Abramis spp.), carp (Cyprinus carpio), perch (Perca fluviatilis), zander (Sander spp.), grass carp (Ctenopharyngodon idella), various catfishes, crayfish, dragonfly larvae, beetles, and frogs.

Although the northern snakehead can survive up to four days out of the water, overland migration is only possible for juveniles (Courtenay and Williams 2004). The rounded body of the adult northern snakehead is not as conducive to overland migration as observed in more horizontally flattened snakehead species.

Potential pathway of introduction: Unauthorized intentional release from aquariums or live food markets

According to the Northern Snakehead Working Group (NSWG) of the U.S. Fish and Wildlife Service, northern snakehead likely arrived in U.S. waters by importation for the live food fish market (NSWG 2006). Unauthorized intentional release from this trade, as was the case in the founding individuals of the Crofton pond population in Maryland, continues to be the major mechanism for introduction (Courtenay and Williams 2004). The northern snakehead has become widely popular in ethnic markets and restaurants over the last two decades, such that this species comprised the greatest volume and weight of all live snakehead species imported into the U.S. until 2001 (Courtenay and Williams 2004, NSWG 2006). In Canada, Herberg et al. (2007) identified two watersheds in the Toronto area along Lake Ontario to be at the greatest risk for northern snakehead introduction from the live fish trade; the Rideau River watershed and Cedar Creek watershed (between Lake Erie and Lake St. Clair) posed additional vectors for introduction. Snakeheads’ resilient nature reportedly makes them more desirable than carps for ceremonial release, and some interest in recreational fishing may also exist (Mendoza-Alfaro et al. 2009, NSWG 2006).

Recognized as a highly injurious species, importation and cross-border transport of northern snakehead was prohibited in the U.S. by a 2002 listing under the Lacey Act and has been subsequently banned in Ontario. Nevertheless, cases of northern snakehead for sale in areas where possession is illegal are not uncommon (NSWG 2006, USGS). Accidental release during transport of live fish is possible, but its probability is unknown (Mendoza-Alfaro et al. 2009).

Channa argus has a moderate probability for establishment if introduced to the Great Lakes (Confidence level: Moderate)

Channa argus is established in Arkansas, Maryland, New York, Pennsylvania, and Virginia, but is not established in California, Illinois, Florida, Massachusetts, or North Carolina, where only a few individual fish have been collected. In March 2009, eradication of the population in Little Piney Creek, Arkansas drainage was attempted through the application rotenone to more 700 km of creeks, ditches, and backwaters  (Holt and Farwick 2009); however specimens were collected in Piney Creek later that year, indicating eradication had not been complete (L. Holt, pers. comm.). The northern snakehead was eradicated from the Crofton pond in Maryland where it was first established, but this species is well established in the Potomac River and several of its tributaries in Virginia and Maryland. The population in Catlin Creek, New York was also treated with rotenone. Although young fish were found, the status of the Philadelphia population is uncertain. Officials believe fish may have gotten into the lower Schuylkill River and Delaware River in Pennsylvania and see no practical means to eradicate them.

The northern snakehead’s broad physiological tolerances, capacity to overwinter—including survival under ice, varied and flexible diet throughout at all life history stages, predatory and competitive nature, high fecundity, and parental investment in offspring (see Ecology section of profile), give this species a suite of favorable attributes for establishment  once introduced. Northern snakehead can adapt to a wide range of aquatic habitats and has been predicted to have high environmental suitability in the northern U.S. and southern Canada, including abundant potential habitat in the Great Lakes (Herborg et al. 2007, Mendoza-Alfaro et al. 2009, NSWG 2006).

Historical imports to the U.S. have come from a wide range of source populations, including Nigeria, Thailand, Indonesia, China, and Korea (NSWG 2006). Orrell and Weigt (2005) found seven unique mitochondrial DNA haplotypes, none of which were shared, among the five U.S. populations they surveyed, indicating separate introduction events and source populations for each. Such high genetic diversity among introduced populations can promote their establishment and spread (Lee 2002, Sanders 2010).

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Socioeconomic

Channa argus has the potential for high environmental impact if introduced to the Great Lakes.

Potential:
Despite its high potential for outcompeting native species for food resources and altering food-web dynamics (Courtenay and Williams 2004, NSWG 2006) due to its voracious predatory nature, wide environmental tolerance, and varied diet, there is little published on the ecological effects of introduced northern snakehead. However, it has been predicted that northern snakehead could substantially modify the ecosystem balance of waters with low diversity and low abundance of native predatory species through top-down mechanisms (Courtenay and Williams 2004, Landis et al. 2011, NSWG 2006).

Among the eight forage fishes consumed by northern snakehead in the Potomac River, banded killifish (Fundulus diaphanus), bluegill (Lepomis macrochirus), pumpkinseed (L. gibbosus), and white perch (Morone americana) were most commonly observed (NSWG 2006). Petr and Mitrofanov (1998) noted that an immigration of fish species to Turkmenistan from Uzbekistan, which included C. argus warpachowskii, caused an observed decline in the number of native species. Furthermore, northern snakehead could highly risk threatened and endangered species. Of all the taxa listed as endangered or threatened in U.S. aquatic habitats, 16 amphibians, 115 fishes, and 5 of the 21 crustaceans (surface dwelling crayfish and shrimp), would be the most likely to be affected (Courtenay and Williams 2004).

Northern snakehead, like many other fishes, is a carrier of non-native parasites and other pathogens (including myxosporidians, cestodes, trematodes, nematodes, acanthocephalans, and copepods; Bykhovskaya-Pavlovskaya et al. 1964), which could potentially have a significant environmental impact on Great Lakes fauna. Working with researchers in Japan, the U.S. Fish and Wildlife Service (USFWS) identified nematodes observed in northern snakehead captured from the Potomac River as eustrongylides, native to U.S. waters; these are typically carried by the killifish the snakehead feeds on (Northern Snakehead Working Group [NSWG] 2006). Additionally, Chiba and others (1989, cited by Courtenay and Williams 2004) noted that C. argus (along with C. maculata) introduced parasites to Japan, but failed to provide details of the parasites involved or fish species affected.

Channa argus has the potential for moderate socio-economic impact if introduced to the Great Lakes.

Potential:
In the Potomac River, the habitat and feeding preferences of northern snakehead appear to overlap with that of the recreationally important largemouth bass (Micropterus salmoides). Northern snakehead  have been observed to consume killifish, an important prey for white and yellow perch, as well as white perch itself (Odenkirk and Owens 2005, cited in NSWG 2006), posing a potential impact on commercial and recreational fisheries.

Although there is little information on parasitic or disease transmission in the scientific literature available, it is known that a related species, C. striata, has been identified as an intermediate host for the helminth parasite that causes gnathostomiasis, a disease that can affect humans. It is still unknown if other snakehead species may serve as an intermediate host for larvae of this parasite (Courtenay and Williams 2004).

The cost of control or eradication, should northern snakehead be introduced to the Great Lakes, could be high. Estimated costs associated with the Crofton, MD eradication effort (limited to a small pond) were over $100,000, and may be financially impossible for larger water bodies (Courtenay and Williams 2004).

Channa argus has the potential for moderate beneficial effects if introduced the Great Lakes.

Potential:
Northern snakehead possesses commercial importance in both native and introduced ranges. It is not only the most important snakehead cultured in China (with most culture activities centered in the Yangtze basin), but it also became commercially valuable in the deltaic area of Syrdarya after its introduction and subsequent naturalization (Aladin et al. 2008, Courtenay and Williams 2004). In addition, this species has historically been imported for sale in live-food fish markets, was previously cultured in Arkansas, and has been the most widely available snakehead in the United States (Courtenay and Williams 2004).

Channa argus is frequently in recreational and cultural activities of some communities. After becoming established in the Potomac River, natural resource managers and law enforcement officials noted and became concerned with the growing interest in fishing for snakehead by the local population (NSWG 2006). In addition, some cultures utilize this species during prayer release (freeing captive animals into the wild as a ceremonial petition) (NSWG 2006).

Though not contributing uniquely significant research value, Chen et al. (2009) purified and characterized pepsinogens and pepsins from northern snakehead In order to investigate the digestive capacity of top-level predators.

Regulations
Under the Lacey Act (18 U.S.C. 42), importation and interstate transport of live snakeheads is banned in the U.S. (67 FR 62193). Possession of live snakeheads is prohibited in all Great Lakes states and provinces (Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania, Wisconsin, and Ontario), as well as in Alabama, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Iowa, Kansas, Kentucky, Louisiana, Maryland, Mississippi, Missouri, Montana, Nebraska, Nevada, New Jersey, North Carolina, North Dakota, Oklahoma, Oregon, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Virginia, and Washington (Courtenay and Williams 2004, IISG 2011, GLPANS 2008).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
Chemical
Rotenone can be used to eradicate northern snakehead from lakes and ponds; however this chemical treatment will also kill non-target fish species (Courtenay and Williams 2004). Rotenone should be applied to the pond or lake with both surface spray application and injected underwater over the entire pond sufficient to achieve a dosage of at least 3 parts per million. It is registered for use in the U.S. and Canada and readily available on the commercial market (Abdel-Fattah 2011).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for chemical control measures.

The August 8, 2010 report of a northern snakehead caught in Canadian waters at the Welland Canal was confirmed instead to be a native bowfin (Carletti and Gillis 2010).