Identification: A long, thin fish with a single dorsal fin running the length of the fish. Overall color is brown with dark blotches. It has a somewhat flattened head with eyes located in a dorsolateral position on the anterior part of the head; anterior nostrils are present and tubular; dorsal and anal fins are elongated, and all fins are supported only by rays (Courtenay and Williams 2004). Males are darker in color, and have a broader head, as compared to females (Gascho Landis and Lapointe 2010). Juveniles have a similar color and pattern as the adults.
The first report of this species in the United States came from Silverwood Lake, California in 1997 (Courtenay and Williams 2004). Two fish were captured from the St. Johns River below Lake Harney in Florida early in 2000. There were unconfirmed reports of another 3 fish nearby. A specimen was collected in Lake Michigan, Burnham Harbor in downtown Chicago, Illinois in 2004 (D. Chapman, pers. comm.). In June 2002, an established population of this species was discovered in a pond in Crofton, Maryland. This population was eradicated by state biologists using rotenone. Fish have been reported from two locations in Massachusetts; once in 2001 and again in 2004. In July 2005, they were reported in Meadow Lake in Queens, New York and persisted in 2006 (J. Pane, pers. comm.). In late May and early June 2008, three snakeheads were collected from stream in Wawayanda, New York (M. Flaherty, pers.comm.). An attempt was made to eradicate this population in 2008.
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.
Two fish were reportedly caught by anglers in August 2002 from Lake Wylie, North Carolina. Five years later in 2007, a large adult was caught by a fisherman in South Fork Catawba River in North Carolina (J. Rash, pers. comm.). In July 2004, several individuals were captured from a pond in FDR Park in Philadelphia, Pennsylvania. The following year young snakeheads were captured in the park pond (R. Worthington-Kirsch, pers. comm.). In June 2008, a specimen was collected by the city water department from the Schuylkill River in Philadelphia (J. Perillo, pers. comm.).
Beginning in April 2004, several fish were captured from the Potomac River in Maryland and Virginia. Although it was originally thought that these fish may have originated from the Crofton pond population, genetic evidence showed that this was an unrelated introduction (Starnes et al. 2011). The Potomac River population now extends throughout the lower Potomac from Great Falls to the mouth, including some tidal portions with moderate salinity (up to 7.6 ppt; Starnes et al. 2011). Another specimen was collected in Dogue River in Fairfax County, Virginia. A fish was collected from Massey Creek and in 2005 a breeding female was found in Little Hunting Creek, a tributary of the Potomac, Virginia. Many others have been collected in 2006 and 2007 in the Potomac basin centering around Dogue and Little Hunting creeks in Virginia and from the Anacostia River in Maryland (J. Odenkirk, pers. comm.). In April 2008, the discovery of a single specimen in a ditch near Monroe, Arkansas, led to the determination that a population appears to be established (L. Holt, pers. comm.). Their first appearance in New Jersey occurred in Delaware River tributaries as early as 2009; they have been caught by fisherman from nearly a dozen streams (C. Smith, pers. comm.). They began to be seen in the state of Delaware in 2010 (C. Martin, pers. comm.) and have been collected from both the lower Delaware and lower Chesapeake drainages.
Ecology: Channa argus is an obligate air-breather, capable of survival in poorly oxygenated waters. Although this species prefers to live in stagnant shallow (< 2 m) ponds or swamps with mud substrate or aquatic vegetation and slow muddy streams, it also occurs in canals, reservoirs, lakes, and rivers (Courtenay and Williams 2004). This species does show some seasonal changes microhabitat selection and preference, utilizing deeper water in winter months and shallow areas with macrophytes during the spawning season (Lapointe et al. 2010). It can adapt to a wide range of aquatic environments, as evidenced by the spread of reproducing, introduced populations throughout Asia and Japan. While its optimum maximum air temperature range is 5-16°C (Herborg et al. 2007), the northern snakehead has a wider latitudinal range and temperature tolerance (0 to >30°C, including frost days) than other snakehead species (Dukravets and Machulin 1978, in Courtenay and Williams 2004; Okada 1960). Reduced metabolism and oxygen demand at low temperatures allows this species to survive extended periods of ice cover (Frank 1970, in Courtenay and Williams 2004). Upper salinity tolerances have been experimentally determined to be between 15 and 18 ppt (at temperatures of 15-24°C; NSWG 2006).
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 (Gascho 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 River 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, Gascho 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; Gascho 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 (Gascho 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, cray fish, 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.
Means of Introduction: Channa argus has a moderate probability of introduction to the Great Lakes (Confidence level: Moderate).
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). Accidental release during transport of live fish is possible, but its probability is unknown (Mendoza-Alfaro et al. 2009).
Status: Established in the United States. Not established in the Great Lakes.
Channa argus is established in Virginia, Maryland, Pennsylvania, New York, and Arkansas, but is not established in California, Florida, Illinois, Massachusetts, Delaware, and North Carolina where a few individual fish have been collected. However, the northern snakehead was eradicated from the Crofton pond in Maryland where it was established. The species is well established in the Potomac River and several of its tributaries in Virginia and Maryland (Starnes et al. 2011). 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. In March 2009, the population in Little Piney Creek drainage received an eradication attempt with the application of rotenone to more 700 km of creeks, ditches, and backwaters. However, more snakeheads have been found since this effort (L. Holt, pers.comm.). The population in Catlin Creek, New York was also treated with rotenone.
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, 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).
References: (click for full references)
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This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.