Channa argus (Northern Snakehead) is native to Pacific river drainages of Asia, from the Amur basin on the Chinese-Siberian (Russia) border to upper tributaries of the Yangtze. It has been successfully introduced to other waters of China, freshwaters of Japan, and the Aral Sea basin of Kazakhstan, and unsuccessfully to the Moscow region of Russia (Courtenay and Williams 2004).
In North America, isolated specimens of Channa argus were collected in Spiritwood Lake, San Bernardino Mountains CA (1997), Volusia County FL, in the St. Johns River (2000), in a pond near Shrewsbury MA (2001), and in Lake Wylie, on the Catawba River NC (2002) (Courtenay and Williams 2004). A population was discovered in northeast AR in 2008, which is now established (USGS Nonindigenous Aquatic Species Program 2011).
The first confirmed established population of C. argus was discovered in the Chesapeake Bay watershed on May 14, 2002, in a small (1.8 ha) retention pond in Crofton MD, not far from the Little Patuxent River, when a 45 cm specimen was caught. In the following months, more than 1,000 juvenile fish were caught durng eradication efforts. The Snakehead story received intense nationwide media coverage, and became a widespread but short-lived cultural phenomenon, spawning cartoons, T-shirts, jokes, etc. On August 18th, the pond was treated with herbicides, in order to aid in detection of fish, and on Septermber 4th, the pond, together with 2 neighboring ponds was treated with rotenone to kill the fish. This treatment was effective- no additional C. argus have been seen in the pond (Dolin 2003; Courtenay and Williams 2004; Huslin 2002; Kobell and Thomson 2002; Thomson 2002).
In April-May 2004, in quick succession, 4 specimens of Channa argus were found in the Chesapeake Bay watershed. On May 26, 2004, a single fish was caught in Pine Lake, in Wheaton (MD) Regional Park, off Sligo Creek, a Potomac tributary in the Washington DC suburbs. The pond was drained, but no additonal snakeheads were found (Faranthold 2004). On May 7, a snakehead was caught in Little Hunting Creek, near Mount Vernon VA on the tidal Potomac River. On May 12, another specimen was caught across the river, near Marshall Hall MD, and on May 15, a third specimen was caught in the Potomac estuary near Mason Neck National Wildlife refuge, a few km downriver from the previous captures (Virginia Department of Fish and Game 2004; Whoriskey 2004). Two more fish were caught in the general area, in Pohick Bay, May 27, and on June 4th, in Dogue creek, near Mount Vernon (Washington Post 2004). By October 1st, 19 fish of varying sizes had been caught by anglers, including 3 egg-bearing females. On this date, a juvenile fish 7.5 cm long was found in a clump of hydrilla tangled in a boat trailer (Virginia Department of Game). Genetic analysis indicates that the fish from Crofton introduced in 2002, the fish from Pine Lake, Wheaton, and the fish captured in the Potomac, in 2004 have different haplotypes, and each represent different introductions. At least 7 separate haplotypes were identified in Northern Snakeheads recently caught in North America, 2 from the Potomac, two from established populations from PA, and a single fish from MA , indicating that multiple introductions have occurred at many locations in North America (Orrell and Weigt 2005).
In October 2005, after a heavy rain, a mass upstream movement of Northern Snakeheads was seen in Dogue Creek, Virginia. Local anglers caught at least 80 fish moving past the remains of a dam (Partlow 2005). A study of snakehead movements using radio tracking found that the fish preferred areas with heavy cover of submerged aquatic plants, especially Eurasian Watermilfoil (Myriophyllum spicatum, and moved into shallower water, and up creeks for spawning in early June. They moved into deeper water in winter (Lapointe et al. 2010). In February, 2006, a snakehead was caught in meshohaline waters of the Potomac, below Rt. 301 and above Colonial Beach, Virginia. in upper Machodoc Creek, at 7.9 ppt (USGS Nonindigenous Aquatic Species Program 2009). In 2010, fish were caught near Kinsale VA, in Hampton Hall Branch, near the mouth of the Potomac, at Kitts Point, at the mouth of St. Marys River, and near Scotland MD, on the open bay between the Potomac and St. Jeromes Creek, streams draining into the Potomac estuary near its mouth (USGS Nonindigenous Aquatic Species Program 2010), suggestive of dispersal through brackish water. In April 2011, a snakehead was caught at White's Ferry, about 56 km (35 miles) above the head of tide on the Potomac, the first capture above Great Falls. The Chesapake and Ohio canal is a possible vector for dispersal above the falls (Sharbell 2011). By 2015, snakeheads were seen regularly above the falls (Zausmer 2015). Based on sampling between 2010 and 2013, and on models of habitat preference and dispersal, Love et al. (2015) estimated that there were 21,279 adult Northern Snakeheads in the Potomac (Love et al. 2015).
In April-July of 2011, several catches of snakeheads were reported in the Bay outside the Potomac River, from St. Jeromes Creek to the Nanticoke River, and up the Bay to the Rhode and Northeast Rivers. These may have resulted from heavy winter and early spring rains which resulted in unusually low salinities in Chesapeake Bay, permitting the fish to disperse widely, although separate introductions are also possible. One fish was caught at Buzz's Marina, in St. Jerome's Creek, on May 3
(Tidalfish.com, http://www.tidalfish.com/forums/showthread.php/302886-Snakehead-caught-today-right-at-Buzz-s-Marina-docks), one near the mouth of the Patuxent, in Middle Creek, north of Solomons (7/10) (USGS Nonnidigenous Aquatic Species Program 2011); another on the Eastern Shore at Wetapquin, MD, in Tyaskin Creek, a tributary of the Nanticoke (6/8/2011, Maryland Department of Natural Resources 2011 http://dnr.maryland.gov/fisheries/fishingreport/). Two additonal fish were caught in nontidal Nanticoke tributaries in DE, one in Marshyhope Creek in July 2011, and one in Broad Creek in the fall of 2010 (WBOC News 7/22/2011, http://www.wboc.com/story/15131544/2-invasive-snakeheads-recently-caught-in-del-waterways). In March of 2012, a snakehead was caught on the Blackwater River (USGS Nonindigeneous Aquatic Species Program 2012). On July 14, one fish, 584 mm long, was caught in a seine in the Rhode River (Ruiz et al, unpublished data; Thomson 7/19/2011). One fish was caught at the head of the Bay, on the Northeast River, on April 17 (4/17/2011, http://dnr.maryland.gov/fisheries/fishingreport/). In July 2012, a Snakehead was caught in a tributary of the Rappahannock River, below Fredericksburg, Virginia, and by 2013, numerous catches were made, and the fish was considered established Nonindigeneous Aquatic Species Program 2013; (Dennen 2013). By May 2013, populations of C. argus appear to be established in the upper tidal Patuxent River, the Choptank, Nanticoke, and Wicomico Rivers, on the MD Eastern Shore, and the Rappahannock River (USGS Nonindigenous Aquatic Species Program 2013).
The likeliest sources of Channa argus in North America are Asian food markets, which frequently sell live imported fish. Snakeheads are highly prized as food in many Asian communities, and are also frequently believed to have medicinal properties (Courtenay and Williams 2004). The origin of the Crofton MD population was a release by a man who had ordered the fish from a New York market, as a remedy for a relative's illness. When the fish were no longer needed, and grew too big to keep, he discarded them in the pond. The Maryland Department of Natural Resources kept the man's name anonymous, and did not prosecute, since the man had violated no laws at the time of the act (Dolin 2003). We consider this introduction to be "accidental", since it was not done with apparent intent to start a population. The source of the later releases is not clear. Young snakeheads of various species are occasionally sold in the aquarium trade, because of their attractive markings and interesting behavior. However, Channa spp. are voracious, grow fast, and tend to quickly wear out their welcome (Courtenay and Williams 2004).
In July 20-23, 2004, 6 Channa argus were caught in Meadow Lake in FDR Park, Philadelphia, a marshy lake, connected by sloughs to the tidal Delaware River (Pennyslvania Fish and Boat Commission 2004). By 2011, C. argus were caught from Delaware tributaries on the outskirts of Trenton (Crystal Lake, Florence-Roebling) downriver to Wilmington DE (Nonesuch Creek, Wilmington Manor (USGS Nonindigenous Species Program 2012). In August 2011, adult fish and 'bucketfuls' of fry were caught in Becks Pond near Glasgow DE, in the drainage of the Christina River, a Delaware River tributary. Delaware conservation officers believe that the fish were deliberately stocked in the pond. (Montgomery 8/20/2011).
In 2005, a third introduced population was found in ponds in Flushing Meadows Corona Park, Queens, New York City. Thses fish have been found in several ponds and lakes in Queens, but have not entered the tidal waters of the Hudson River or Long Island Sound. Yet another population was found in the upper Hudson watershed, in lakes near Wayawanda NY, north of the Catskills in 2008 (USGS Nonidigenous Species Program 2016). An overview of the genetics of C. argus in North America found that the Chesapeake Bay animals were derived from one introduction in the Potomac, while the Delaware, and the upper and lower Hudson watershed populations were related to snakeheads bought in a Chinese market in New York City. This suggests that there were at least two separate introductions to the northeast US from Asia (Wegleitner et al. 2016).).
References- Courtenay and Williams 2004; Dolin 2002; Farenthold 2004; Farenthold and Partlow 2004;Huslin 2002; Kobell and Thomson 2002; Orrell and Weigt 2005; Partlow 2005; Pennyslvania Fish and Boat Commission 2004; Thomson 2002; Virginia Department of Game and Inland fisheries 2004a; Virginia Department of Game and Inland fisheries 2004b; Whoriskey 2004