Snakeheads (family Channidae) are morphologically similar to the North American native Bowfin (Amia calva), and the two are often misidentified. Morphological differences used for identification between the two are depicted here. 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 (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.

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).

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).

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Ecological	Economic	Other

A specimen collected from Lake Wylie, North Carolina, in 2009 was originally identified as Channa argus, but later genetic work combined with a closer morphological analysis determined the specimen to be Channa maculata (NCSM 53258; W. Starnes, personal communication).