Channa argus argus (northern snakehead)
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PicturesTop of page
|Title||Adult northern snakehead|
|Caption||Adult northern snakehead (Channa argus argus).|
|Adult northern snakehead||Adult northern snakehead (Channa argus argus).||Osamu Tango|
IdentityTop of page
Preferred Scientific Name
- Channa argus argus (Cantor, 1842)
Preferred Common Name
Other Scientific Names
- Channa argus Cantor, 1842
- Channa argus kimurai Shih, 1936
- Ophicephalus argus Cantor, 1842
- Ophicephalus nigricans Cuvier, 1831
- Ophicephalus pekinensis Basilewsky, 1855
- Ophiocephalus argus Cantor, 1842
- Ophiocephalus argus warpachowskii Berg, 1909
International Common Names
- English: amur snakehead; eastern snakehead; ocellated snakehead; snakehead; striped murrel
Local Common Names
- China: her-yu; wu li
- Denmark: kinesisk slangehovedfisk
- Finland: amurinkaameenpaa; idankaarmeenpaa
- France: poisson tete de serpent
- Germany: amur-schlangenkopf
- Japan: kamuruchi; raigyo
- Korea, Republic of: ga mul cji
- Russian Federation: zmeegolov
- Spain: cabeza de serpiente
Summary of InvasivenessTop of page
The northern snakehead, or the Raigyo (thunder fish) as it is known in Japan, is a native of southern and eastern China and was introduced to Japan from Korea in the early 1900s (Masuda et al. 1984; Chiba et al. 1989). The snakehead inhabits shallow, marshy ponds and wetlands and is widely distributed in Japan where it preys on native fish species. An obligate air breather, it can survive out of water for up to four days and commonly escapes from ponds it has been introduced to, dispersing into new areas and establishing populations relatively quickly in new water bodies. In 2002, the species was discovered in a pond in Crofton, Maryland, USA as a result of its purchase in New York and later release into Maryland waters (Kluger, 2002). Its first discovery in the USA sparked national media attention, featuring in both regional and national newspapers and news programmes (Fuller, 2003). Since its first sighting in the USA, northern snakeheads are now prevalent throughout the country and can be found in California, Florida, Maine, Maryland, Massachusetts, Arkansas, North Carolina, Rhode Island, and Wisconsin. The species is not involved in the aquarium fish trade but is sold in live food fish markets as a food fish. The most likely pathway is the introduction of live food fish, perhaps to establish a local market (USGS, 2003).
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Chordata
- Subphylum: Vertebrata
- Class: Actinopterygii
- Order: Perciformes
- Suborder: Channoidei
- Family: Channidae
- Genus: Channa
- Species: Channa argus argus
DescriptionTop of page
The northern snakehead, C. argus argus, has a long torpedo-shaped body that tapers towards the tail, long, single dorsal (49-50 fin rays) and anal (31-32 fin rays) fins. It has a small head, a large mouth and numerous sharp villiform teeth present in bands, with some large canine-like teeth on the lower jaw and palatines (Cudmore and Mandrak, 2006). The pelvic fins originate below the fourth dorsal ray and the pectoral fins extend beyond the base of the pelvic fins (Courtenay and Williams, 2004). It exhibits a truncated tail, and can grow up to 85 cm in length (Okada, 1960). However, some Russian specimens have been reported as being greater than 1.5 m in total length (Courtenay and Williams, 2004). The body fins are yellow. The dorsal, anal and caudal fins are spotted black (Amanov, 1974). There are 60-75 scales in the lateral line. Sexing of this fish by external morphology is difficult and can only be accurately determined in sexually mature individuals. The species is sexually dimorphic with the male fish being larger and more robust than the females and having a higher dorsal fin, wider interorbital distance, and a longer snout, postorbital distance and upper jaw (Duvrakets and Machulin, 1978).
A key characteristic of northern snakeheads are their distinctive colour patterns, which vary according to specific habitat attributes and can change rapidly. Juveniles are virtually the same in colouration as the adults; a characteristic atypical for many snakehead species. Juveniles may be gold-tinted brown to pale grey in colour, whereas older fish are easily identified by a series of 9-13 dark blotches along their sides set against a background of golden tan or light brown (Sea Grant Pennsylvania, 2012). These blotches have a lighter centre that is sometimes edged in white, above the lateral line. There is a prominent dark stripe extending from the posterior margin of the eye orbit to the upper edge of the operculum. A second dark stripe extends from below the posterior orbit to the lower section of the operculum.
Scales are absent from the gular regions of the head. Lateral line scales number 60-67, with eight scale rows above the lateral line to the origin of the dorsal fin and 12-13 scale rows below the lateral line to the origin of the anal fin. Large scales are observed on the top of the head and are similar to the cephalic plates, which are observed in many species of snake worldwide. Parietal scales are of moderate-size, with a rosette of head scales between the orbits, and a frontal head scale at the centre (Courtenay and Williams, 2004).
Morphometrics of this fish are described as:
standard length: 84.9% total length (TL)
fork length: 100% TL
pre-anal length: 44.7% TL
pre-dorsal length: 30.1% TL
pre-pelvic length: 31.6% TL
pre-pectoral length: 29.9% TL
body depth: 12.7% TL
head length (HL): 28.6% TL
eye diameter: 12.4% HL
pre-orbital length: 15.4% HL (Kim, 1997).
DistributionTop of page
The northern snakehead is native to the rivers of China southward and south-westward to the upper tributaries of the Chang Jiang (Yangtze) River basin in north-eastern Yunnan Province to Peking, the Liao, Yalu, and Lianzi Lakes, and upper reaches of the Beijiang River in Guangdong Province (Baensch and Riehl, 1985; Xinluo and Yinrui, 1990; Ruihua, 1994) likely as the result of an introduction there. It is widely distributed in Chinese reservoirs (Sifa and Senlin, 1995). It is found in Russia, in the Middle and lower Heilong (Amur) River basin, Songhua (Sungari) River, Manchuria and Tunguska River at Khabarovsk, Ussuri River basin, Lake Khanka (Herzenstein and Warpachowski, 1887; Berg, 1965; Popova, 2002; Reshetnikov et al., 1997). It is also found throughout the rivers of Korea with the exception of the north-eastern regions (Okada, 1960; Berg, 1965; Froese and Pauly, 2013).
C. argus argus has been introduced to non-native locations in China and Russian Federation, as well as in Japan, Kazakhstan, Turkmenistan, Uzbekistan and the USA.
The northern snakehead was reported to be the dominant snakehead in China (Shih, 1936). This snakehead can be found in rivers, streams and ponds across China from Yunnan to Beijing. According to Shih (1936) the fish has been found in the River Kialing in Sichuan Province, China, where it was reported to be common in the rice fields as well as mountain streams. Reeves (1927) reported C. argus argus north-east of China and Korea. In South-East Asia, this fish lives in irrigation ditches and rice paddies, thriving there until the dry season, when the pools shrink and the fish moves along to the next pocket of water. From further north, into Russia, in the region of the River Amur, hails the hardier northern snakeheads which have been successfully introduced to many countries, including the former Czechoslovakia.
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
|Country||Distribution||Last Reported||Origin||First Reported||Invasive||References||Notes|
|Cambodia||Absent, invalid record||Invasive||Northern Snakehead Working Group, 2007|
|China||Present||Native||Froese Pauly, 2009; Courtenay & Williams, 2004|
|-Hebei||Present||Native||Invasive||Baensch & Riehl, 1985|
|-Hong Kong||Absent, invalid record||Introduced||Northern Snakehead Working Group, 2007|
|-Jiangsu||Present||Native||Invasive||Baensch & Riehl, 1985|
|-Jilin||Present||Native||Invasive||Baensch & Riehl, 1985|
|-Liaoning||Present||Native||Invasive||Baensch & Riehl, 1985|
|-Sichuan||Present||Native||Invasive||Baensch & Riehl, 1985|
|-Yunnan||Present||Native||Invasive||Baensch & Riehl, 1985|
|Japan||Present||Introduced||Invasive||Froese Pauly, 2009; Courtenay & Williams, 2004|
|-Honshu||Present||Introduced||Invasive||Masuda et al., 1984|
|Kazakhstan||Present||Introduced||Invasive||USGS, 2003; Courtenay & Williams, 2004||Established in the Aral Sea|
|Korea, DPR||Present||Native||Not invasive||USGS, 2003|
|Korea, Republic of||Present||Native||Food and Agriculture Organization, 1997; Froese Pauly, 2009; W. Courtenay, USGS, USA, personal communication, 2010|
|Thailand||Absent, invalid record||Introduced||Northern Snakehead Working Group, 2007|
|Turkmenistan||Present||Introduced||Courtenay & Williams, 2004|
|Uzbekistan||Present||Introduced||USGS, 2003; Courtenay & Williams, 2004|
|Vietnam||Absent, invalid record||Introduced||Northern Snakehead Working Group, 2007|
|Nigeria||Present only in captivity/cultivation||Introduced||Not invasive||Northern Snakehead Working Group, 2007|
|USA||Present||Introduced||Froese Pauly, 2004|
|-California||Present||Introduced||Invasive||Fish and Wildlife Service, 2002; USGS, 2003|
|-Maine||Present||Introduced||Invasive||Fish and Wildlife Service, 2002|
|-Maryland||Present||Introduced||Invasive||Fish and Wildlife Service, 2002|
|-Massachusetts||Present||Introduced||Invasive||Fish and Wildlife Service, 2002|
|-North Carolina||Present||Introduced||Invasive||USGS, 2003|
|-Rhode Island||Present||Introduced||Invasive||Fish and Wildlife Service, 2002|
|Czechoslovakia (former)||Present||Introduced||Courtenay & Williams, 2004|
|Russian Federation||Present||Native||Not invasive||Froese Pauly, 2009|
|-Russian Far East||Present||Native||Invasive||Reshetnikov et al., 1997|
|Slovakia||Present||Introduced||Courtenay & Williams, 2004|
History of Introduction and SpreadTop of page
The presence of this species in the upper reaches of the Bei (Beijiang) River, Guangdong Province, China, is apparently the result of an introduction (Pearl River Fisheries Research Institute, 1991). It was unintentionally introduced from Korea in the early 1900s and has become successfully established in many waters of central and southern Japan including Hokkaido, Honshu, Kyushu, and Shikoku (Nakamura, 1963; Uyeno and Akai, 1984; Okada, 1960; Courtenay and Williams, 2004).
Despite several attempts beginning in 1949, northern snakeheads intentionally introduced to a variety of waterbodies in Czechoslovakia failed to become established for a variety of reasons (Frank, 1970; Holcik, 1991). However, successful introductions and establishments of snakehead populations have occurred throughout Russia and surrounding regions (Bogutskaya and Naseka, 2002). In the early 1960s, C. argus argus was introduced into the Aral Sea basin (about 45ºN) and subsequently dispersed to the Amu Dar’ya, Syr Dar’ya, and Kashka-Dar’ya rivers of Kazakhstan, Uzbekistan, and Turkmenistan (Borisova, 1972; Amanov, 1974; Dukravets and Machulin, 1978; Usmanova, 1982; Guseva, 1990; Dukravets 1992). The species is now likely extirpated from the Aral Sea due to environmental change and a notable increase in salinity beyond the tolerance limits of snakeheads as a result of evaporation and water loss (Courtenay and Williams, 2004).
The initial introduction of the northern snakehead to Russia was unintentional and was as a result of contamination in stocking phytophagous cyprinids (grass carp, Ctenopharyngodon idella, and silver carp, Hypophthalmichthys molitrix), destined for aquaculture in ponds adjacent to the Syr Dar’ya River. Snakeheads escaped from the ponds in 1964 and soon became established in the Syr Dar’ya (Amanov, 1974). Many other examples exist where snakeheads, which have a strong tendency to escape from ponds, have been introduced and then escaped and subsequently dispersed to new water bodies resulting in the establishment of new populations. Their ease of dispersal further illustrates the significant risk posed to North America following their establishment in the United States.
Introductions into western Asia and eastern Europe were thought by some, to have originated from China, perhaps from the Amur basin stock of C. argus argus. The species thrives in irrigation reservoirs and isolated ponds on the Talas River, and more than 10 metric tons of fish were commercially harvested from these reservoirs in 1989 (Dukravets, 1992). The latitude of this area of Kazakhstan is similar to that of the Vermont/Quebec border, Minneapolis, Minnesota, and Salem, Oregon, in North America, which indicates a successful establishment at the northern range of distribution and confirms the risk should this snakehead become further established in North American (Courtenay and Williams, 2004).
In the United States, a large snakehead was captured by electroshocking in Spiritwood Lake, located in the San Bernardino Mountains, north of San Bernardino, California, on October 22, 1997. While the species identification of the specimen is not possible, it is unlikely that any other species of snakehead could survive in this high-altitude reservoir (Courtenay and Williams, 2004).
Two specimens were captured from the St. Johns River below Lake Harney, Seminole and Volusia Counties, Florida. Attempts to confirm a population of snakehead in this location have so far been unsuccessful by USGS personnel; however, additional attempts to collect the species will be undertaken (Courtenay and Williams, 2004).
On May 14, 2002 a Maryland angler caught a 43-45 cm long snakehead in a 1.8-ha retention pond behind a shopping mall in Crofton, Anne Arundel County, Maryland. Subsequent collections by both angling and dipnetting resulted in the identification of an established and reproducing population in these ponds. Eradication methods were employed and revealed nearly 1400 specimens of varying size classes were present.
Additional collections of snakeheads were made in Newton Pond, Massachusetts and Charlotte, North Carolina with an unconfirmed report from Rockport, Texas as well. These widespread occurrences of introductions are likely attributed to intentional release from the live food fish markets in the regions, presenting a difficult management situation (Courtenay and Williams, 2004).
Risk of IntroductionTop of page
The northern snakehead has the potential for widespread establishment due to a much broader latitudinal range and thermal tolerance than most other snakehead species. The region at risk of invasion and subsequent establishment includes most of the contiguous United States and some regions of southern Canada (Courtenay and Williams, 2004). The results of a formal Risk Assessment conducted by the Center of Expertise for Aquatic Risk Assessment, Department of Fisheries and Oceans Canada prepared by Cudmore and Mandrak (2006) Part I (Aquatic Organism Ecological and Genetic Risk Assessment Process) revealed a "High probability of establishment estimate" (reasonably certain) and a "High consequences of establishment estimate" (reasonably certain), giving a "Final Risk Estimate" of "High" (reasonably certain) for northern snakehead in the Great Lakes basin. Similarly, Part II (Pathogen, Parasite or Fellow Traveler Risk Assessment Process) revealed a "Medium probability of establishment estimate" (reasonably certain) and a "Medium consequences of establishment estimate" was "Medium" (very uncertain), giving a "Final Risk Estimate" of "Medium" (very uncertain).
The species is well established in Kazakhstan, the latitude of which is similar to that of the Vermont/Quebec border, Minneapolis, Minnesota, and Salem, Oregon, in North America, which indicates a successful establishment at the northern range of distribution and confirms the risk should this snakehead become further established in North American (Courtenay and Williams, 2004).
The northern snakehead may be introduced for a number of reasons despite imposed legislation.
It is the most important snakehead cultured in China (Courtenay and Williams, 2004) where it is grown in ponds, rice paddies, and reservoirs (Liu et al., 1998). Prior to changes to federal legislations in 2002 which resulted in a ban on the possession, culture and transportation of northern snakehead, it was cultured in fish farms from Arkansas (Courtenay and Williams, 2004).
The northern snakehead, due to their aggressive nature and strength, have been introduced into a number of locations for culture as a sport fish (Courtenay and Williams, 2004).
Internet sales/postal services
Despite federal legislations in the United States which prevent importation and transportation of all snakehead species into and between the continental USA, hobbyists and importers are able to purchase snakeheads through a variety of sites on the Internet (Courtenay and Williams, 2004). Live specimens have been traced back to distributors from within the United States and are easily available to fish markets despite federal legislations.
Live food trade
Many introductions of the northern snakehead are believed to be the result of intentional release of fish obtained from the live food trade (Courtenay and Williams, 2004). The northern snakehead is highly prized in Asian markets and is cultured extensively in China and Korea (Courtenay and Williams, 2004). This species has been exported to other nations, including Canada and the United States where it has been sold in the live food fish industry to various ethnic markets and restaurants (Courtenay and Williams, 2004).
It is a popular aquarium fish in Europe and Japan, however, because of their highly predacious nature and the significant costs associated with feeding and housing this species, snakeheads have not generated a large following of interested hobbyists in the USA or Canada (Courtenay and Williams, 2004). Some introductions are believed to have been the result of the intentional release of unwanted aquarium fish (Courtenay and Williams, 2004).
HabitatTop of page
The northern snakehead exhibits a broad tolerance to a wide range of environmental conditions and is extremely hardy (Cudmore and Mandrak, 2006); it may inhabit freshwater environments which can range from 0 to 30°C (Courtenay and Williams, 2004). Northern snakeheads prefer stagnant shallow ponds or swamps with mud substrate and aquatic vegetation; they can also be found in slow muddy streams (Courtenay and Williams, 2004) and in canals, springs, reservoirs, lakes, and rivers (Dukravets and Machulin, 1978; Dukravets, 1992). An obligate air breather it can survive out of water for up to four days by breathing oxygen from the atmosphere. Cold temperatures reduce the fish’s metabolic rate and oxygen demand, which allows it to survive during periods of ice cover (Courtenay and Williams, 2004).
In South-East Asia, this fish lives in irrigation ditches and rice paddies, thriving there until the dry season, when the pools shrink and the fish squirms along to the next pocket of water. Such clumsy locomotion does not lend itself to wanderlust, and snakeheads in a suitable pond are likely to stay there forever.
Habitat ListTop of page
|Irrigation channels||Secondary/tolerated habitat||Productive/non-natural|
|Rivers / streams||Principal habitat||Natural|
Biology and EcologyTop of page
The diploid chromosome number of C. argus argus is 48 (Lee and Lee 1986, Wu et al. 1986). The DNA content/n is: 0.77 pg (Cui et al., 1991).
The northern snakehead reaches sexual maturity at two to three years of age (30 to 35 cm total length (TL)). Females are iteroparous (repeated reproductive events) and are capable of spawning one to five times per year (Courtenay and Williams, 2004). Fecundity is variable and ranges from 1300-15,000 eggs (average 7300 eggs) per spawning event. Fecundity of individuals from the Amur basin appears to be higher than average, ranging from 21,000 to 51,000 per event, often exceeding 100,000 eggs produced annually (Nikol’skiy, 1956; Frank, 1970). Spawning takes place in areas of low turbidity with submerged vegetation and occurs between May and July. During the spawning season, sexually mature fish are highly active and may jump about on the water surface.
Male snakehead construct mostly circular nests of shallow aquatic vegetation, nearly 1 m in diameter and 60-80 cm in depth. Both the male and female snakehead clear any vegetation that is floating above the nest. Spawning typically occurs on calm days, often before sunrise. Fertilization is external and occurs following egg deposition above the nest (Courtenay and Williams, 2004). The eggs are yellow in colour, pelagic, and buoyant due to the presence of a large lipid droplet which occupies more than three-quarters of the egg’s 2 mm diameter (Courtenay and Williams, 2004). Hatching occurs approximately 28 hours post-deposition in waters at 31°C, and 45 hours at 25°C. At lower temperatures, development and hatching takes significantly longer (120 hours at 18°C, Courtenay and Williams, 2004). Care of eggs and fry is bi-parental and occurs until juveniles are approximately 4-5 cm in length, typically around four weeks of age (Courtenay and Williams, 2004). Minimum population doubling time is less than 15 months (Courtenay and Williams, 2004; Froese and Pauly, 2009).
Larvae are about 4.5 mm long at hatching, and are approximately 11 mm within 14 days. At this stage, the yolk sacs have been absorbed, fin rays are visible and the larvae are black in colouration. Within four weeks larval fish have reached a length of approximately 20 mm. The pelvic fins have developed, the epibranchial breathing structures are functional and body colouration becomes brown. At the stage of development, larvae reduce their tendencies for aggregation with conspecifics and migrate to deeper waters. Scales develop in juvenile fish between 4-4.5 cm TL (Courtenay and Williams, 2004).
The northern snakehead is a long-lived fish species, with one specimen recorded as attaining eight years of age and a length of 760 mm TL (Courtenay and Williams, 2004; Froese and Pauly, 2009; Galveston Bay Invasive Species Risk Assessment, 2002).
The northern snakehead is a voracious eater and predates upon a wide range of aquatic fauna. Post-larval snakeheads feed upon zooplankton, but once they are juveniles or have reached 4 cm in length, they consume larger food items such as crustaceans and insects. Typically, juveniles at a length of 13-15 cm will mainly feed on fish, which can represent 64-70% of their dietary intake. Once adult sizes of 30 cm or more have been attained, the diet of the northern snakehead is nearly exclusively piscivorous, although frogs, crustaceans, and even small reptiles, birds, and mammals may also be consumed (Courtenay and Williams, 2004). Plants and phytoplankton seem to be ingested incidentally (Hilton, 2002).
This species has been observed consuming prey almost one third of its own body length (Okado, 1960; Courtenay and Williams, 2004). Larger prey items often include loach, bream, carp and perch; whereas, other food items include crayfish, dragonfly larvae, beetles and frogs (Courtenay and Williams, 2004). Gut content analysis of the northern snakehead (n=219) from the Potomac River (2004-2006) indicated 17 different food items, including 15 fish species (Odenkirk and Owens, 2007). Primary prey items consisted mainly of banded killifish (Fundulus diaphanous); however, white perch (Morone americana), bluegill (Lepomis macrochirus) and pumpkinseed sunfish (Lepomis gibbosus) were also commonly consumed (Odenkirk and Owens, 2007). Goldfish (Carassius auratus), gizzard shad (Dorosoma petenense), American eel (Anguilla rostrata), yellow perch (Perca flavescens), largemouth bass (Micropterus salmoides), spottail shiner (Notropis hudsonius), eastern silvery minnow (Hybognathus regius), mummichog (Fundulus heteroclitus), channel catfish (Ictalurus punctatus), green sunfish (Lepomis cyanellus), tessellated darter (Etheostoma olmstedi), frogs and crayfish were also consumed at low levels (Odenkirk and Owens, 2006; Northern Snakehead Working Group, 2007).
Most feeding activity occurs during early and late daylight hours, where the species lies in wait for prey in vegetation near shorelines of ponds or streams. Feeding activity is highly correlated with water temperature, with feeding rates highest between 20-27°C. Feeding rate declines as temperatures drop to 12-18°C and ceases if water temperatures fall below 10°C (Courtenay and Williams, 2004).
Natural Food SourcesTop of page
|Food Source||Life Stage||Contribution to Total Food Intake (%)||Details|
|fish, small reptiles, birds, mammals||Adult/Broodstock||100|
ClimateTop of page
|A - Tropical/Megathermal climate||Tolerated||Average temp. of coolest month > 18°C, > 1500mm precipitation annually|
|C - Temperate/Mesothermal climate||Preferred||Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C|
Air TemperatureTop of page
|Parameter||Lower limit||Upper limit|
|Mean maximum temperature of hottest month (ºC)||22||30|
|Mean minimum temperature of coldest month (ºC)||0|
Water TolerancesTop of page
|Parameter||Minimum Value||Maximum Value||Typical Value||Status||Life Stage||Notes|
|Dissolved oxygen (mg/l)||5||8||Optimum||Adult|
|Salinity (part per thousand)||0||Optimum||Adult|
|Water pH (pH)||6.0||7.5||Optimum||Adult|
|Water temperature (ºC temperature)||0||30||Harmful||Highly correlated with feeding frequencies|
|Water temperature (ºC temperature)||10||27||Optimum||Highly correlated with feeding frequencies|
Pathway CausesTop of page
|Aquaculture||Yes||Yes||Courtenay & Williams, 2004|
|Breeding/ propagation||Yes||Yes||Courtenay & Williams, 2004|
|Escape from confinement/ garden escape||Yes||Yes||Courtenay & Williams, 2004|
|Fisheries||Yes||Yes||Courtenay & Williams, 2004|
|Food||Yes||Yes||Courtenay & Williams, 2004|
|Hitchhiker||Yes||Yes||Courtenay & Williams, 2004|
|Hunting/angling/sport/racing||Yes||Yes||Courtenay & Williams, 2004|
|Intentional release||Yes||Yes||Courtenay & Williams, 2004|
|Interbasin transfers||Yes||Yes||Courtenay & Williams, 2004|
|Interconnected waterways ||Yes||Courtenay & Williams, 2004|
|Internet sales||Yes||Yes||Courtenay & Williams, 2004|
|Live food/feed trade||Yes||Yes||Courtenay & Williams, 2004|
|Pet/aquarium trade||Yes||Yes||Courtenay & Williams, 2004|
|Self-propelled||Yes||Courtenay & Williams, 2004|
Impact SummaryTop of page
|Fisheries / aquaculture||Negative|
Economic ImpactTop of page
The northern snakehead is a ravenous fanged predator that threatens the survival of every fish in the same body of water. This exotic creature that can grow to over 90 cm long and weigh up to 15 kg can eat any economically important fish species. During the summer of 2002, several individuals of northern snakeheads were found in a pond in Crofton, Maryland, USA. The potential impact of this introduced species was considered so damaging that the event made national headlines in the USA. Officials posted signs encouraging anglers to kill any snakeheads that they caught. It is illegal to possess snakeheads in 13 states in the USA (2004).
Environmental ImpactTop of page
Impact on Habitats
Northern snakeheads have the ability to significantly impact the function of ecosystems and food webs among native biotic communities. Its establishment in an existing biological community would produce cascading impacts to the food chain by reducing the abundance of planktivorous fish through predation, thus enhancing the abundance of zooplankton and reducing the abundance of phytoplankton. These changes would have energetic implications for the entire aquatic ecosystem.
As a species which is capable of exploiting a wide range of environmental conditions as indicated by its native range (24-53º N) and temperature tolerance (0-30 ºC), this indicates that should northern snakehead be introduced, it is very likely that a population could be successfully established throughout the United States and Canada. Due to the successful establishment in Maryland in 2002, and possibly in Florida, and as a result of its convenient accessibility in the aquarium, live-food fish and internet sales markets, the likelihood of its becoming more widely established is highly likely.
Impact on Biodiversity
The northern snakehead is a voracious, apex predator with few, if any, natural enemies. The species has tremendous potential to severely impact native populations of fishes as well as other crustaceans, insects and other biota. Snakehead are able to negatively impact native populations at all lifestages, from egg predation to consumption of adult fishes. Additionally, cascading effects at all trophic levels promote monoculture of snakehead in non-native waterbodies. Northern snakehead are able to tolerate habitats with extremely low dissolved oxygen content which provides a competitive advantage over native species such as pike (Esox sp.) or bass (Micropterus sp.) (Sea Grant Pennsylvania, 2012). An established population of snakeheads in Maryland could have long-term disastrous consequences for the ecology and biodiversity of the region (Hilton, 2002).
The fish can breathe air and survive for up to four days out of water, and can survive for longer periods of time when burrowed in the mud. These features are adaptive to the seasonal drying of shallow bodies of water in the snakehead native habitat in China. Once a habitat is no longer suitable and native populations have been decimated, snakehead are capable of dispersing overland to exploit new environments and populations. This enables widespread dispersal of a highly fecund population of an invasive species with significant impacts at all trophic levels.
In its native range it can live in water with temperatures of 0-30°C and it is likely that given the wide range of habitats available in North America, suitable conditions exist to support widespread invasive establishment of northern snakehead throughout the United States and Canada.
It is also a vector for disease and parasites, a number of which have been documented as affecting native species. Parasites include Mysosoma acuta (also affects crucian carp), Henneguya zschokkei (also affects salmonids), Cysticercus gryporhynchus cheilancristrotus (also affects cyprinids, perches), Clinostomum complanatum (also affects perches) and Paracanthocephalus cutus (also affects cyprinids, escocids, sleepers and bagrid catfish) (Courtenay and Williams, 2004). The northern snakehead are also known to be susceptible to epizootic ulcerative syndrome (EUS), a disease with a number of known pathogens (Cudmore and Mandrak, 2006). However, in Canada, only a single cyprinid genus (Cyprinus) is known to be affected by EUS.
Social ImpactTop of page
Social consequences may exist should a population of snakehead become established, which negatively impacts commercial fisheries or other industries resulting in economic losses or reduction in quality of recreational usage of waterbodies. Cultural ramifications may be experienced, but more likely would be the economic and recreational losses of affected communities.
Human health may be impacted by zoonotic diseases attributed to snakehead fishes. Gnathostomiasis, a disease which may be transmitted to humans as a result of the helminth parasite (Gnathostoma spinigerum), relies on the chevron snakehead (Channa striata) as an intermediate host in the disease cycle (Cudmore and Mandrak, 2006).
Risk and Impact FactorsTop of page
- Competition - monopolizing resources
- Interaction with other invasive species
- Pest and disease transmission
- Rapid growth
- Altered trophic level
- Damaged ecosystem services
- Damages animal/plant products
- Ecosystem change/ habitat alteration
- Host damage
- Increases vulnerability to invasions
- Modification of natural benthic communities
- Modification of nutrient regime
- Monoculture formation
- Negatively impacts agriculture
- Negatively impacts animal health
- Negatively impacts animal/plant collections
- Negatively impacts aquaculture/fisheries
- Negatively impacts cultural/traditional practices
- Negatively impacts human health
- Negatively impacts livelihoods
- Negatively impacts tourism
- Reduced native biodiversity
- Threat to/ loss of endangered species
- Threat to/ loss of native species
- Abundant in its native range
- Capable of securing and ingesting a wide range of food
- Fast growing
- Has a broad native range
- Has high reproductive potential
- Highly mobile locally
- Invasive in its native range
- Is a habitat generalist
- Long lived
- Proved invasive outside its native range
- Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
Likelihood of entry/control
- Difficult/costly to control
- Highly likely to be transported internationally deliberately
- Highly likely to be transported internationally illegally
UsesTop of page
Although the northern snakehead is regarded a valuable food fish, it has not been cultured on any regular basis. Demand for the food market was met mainly by angling for wild-caught fisheries and using other collection traps devised by local fishermen for use in rivers, canals, lakes and flooded rice fields. As the popularity of the fish has increased, the catches from the wild could not meet the demand, and the resulting market price has created much interest in the aquaculture of snakeheads.
Snakeheads have long been favoured as food fishes in India and many parts of Asia, particularly south-eastern Asia (Berg, 1965; Lee and Ng, 1991; Courtenay and Williams, 2004). Some are utilised as luxury specialty foods, available alive in aquaria for customer selection at upscale restaurants in larger cities such as Calcutta, Bangkok, Singapore, Hong Kong and other major locales. They also provide easily caught food for poorer people (Wee, 1982; Courtenay and Williams, 2004). C. argus argus is the most cultured snakehead in China and the most available snakehead in North American live-food markets. It is of modest importance in the aquarium fish trade in Japan, Europe and to a lesser extent, the USA, although it is reportedly the most available species of snakehead for aquarium usage (Courtenay and Williams, 2004).
In tributaries of the Aral Sea, Kazakhstan, 1-5 metric tonnes of snakehead are fished commercially every year and this amount may increase to 10 metric tonnes annually in reservoirs of the Talas River, Kazakhstan (Baltz, 1991; Dukravets, 1992).
In some cultures, snakehead fishes are thought to confer good-health and longevity to those in possession of it.
Uses ListTop of page
Human food and beverage
- Canned meat
- Cured meat
- Fresh meat
- Frozen meat
- Live product for human consumption
Similarities to Other Species/ConditionsTop of page
The northern snakehead is similar in colouration to the blotched snakehead, Channa maculata. The two species are most easily differentiated by the dark markings observed on the caudal peduncle. In C. maculata, the most posterior dark mark is a bar-like shape and is bordered by pale, bar-like areas, whereas, in C. argus argus, the final bar is more irregular in shape and lacks the pale areas preceding and following the blotch (Courtenay and Williams, 2004).
The species may also be confused with the bowfin (Amia calva) which can be distinguished by having only a long dorsal fin and a short rounded anal fin, rather than having both dorsal and anal fins which are long, and the pelvic fins are inserted more posteriorly on the body. Bowfin lack parietal scales and possess a prominent dark eyespot with a golden halo near the caudal peduncle. A large, gular plate is also a defining characteristic of the bowfin which is not shared by any snakehead species.
Burbot (Lota lota) are also similar in appearance to the northern snakehead but they have a split dorsal fin, the origin of the pelvic fins insert anterior to the pectoral fins, and they possess a single barbel on the lower jaw.
Prevention and ControlTop of page
All members of the family Channidae, including C. argus argus have been identified by the US Fish and Wildlife Service on the federally regulated list of injurious fishes and are banned from importation and interstate transport in the USA since October 2002 by the US Fish and Wildlife Service under the Lacy Act. In the USA, anglers and commercial fisherman have been asked to kill and freeze all snakeheads rather than re-release them and immediately report them to the local Fish and Game Department (Sea Grant Pennsylvania, 2012).
The potential to eradicate or control snakehead populations depends on dispersal location and the level of establishment. If broadly dispersed in large lakes or river systems, eradication or control would likely be impossible. Management options for population control within smaller waterbodies are dependent upon the amount of aquatic vegetation, accessibility of the waterbody, and the effectiveness of the control techniques employed (Hoffman, 2002).
Effective removal strategies for established populations of snakehead must rely on several methods to eradicate the species from non-native waterbodies due to their uncommon biological attributes. Chemical removal using piscicides, such as Rotenone, which acts to impede oxygen availability to fish may not be very effective against C. argus argus due to its ability for air breathing and would likely only result in the removal of non-target species; however, it was a successful eradication method for the Crofton ponds in Maryland (see below for further discussion). Similarly, electrofishing and netting would provide a level of population control, however, would be ineffective across all size classes.
Location Specific Management Information
An attempt was made to eradicate C. argus argus in Arkansas in 2007 by U.S. Fish and Wildlife Service; however, the effort was unsuccessful and cost more than $750,000 (W. Courtenay, USGS, USA, personal communication, 2010).
Following the confirmation of an established population in a 1.8 ha retention pond in Crofton, Maryland, the pond and two adjacent waterbodies were treated with herbicides (Diquat Dibromide and Glyphosate (Hilton 2002)) to lower oxygen levels on 18 August 2002. On the 4th September 2002, a piscicide (Rotenone) was used to successfully exterminate the population (W. Courtenay, USGS, USA, personal communication, 2010). A report which identifies planning methods and details of the eradication techniques employed in the Crofton ponds is available at http://www.dnr.state.md.us/irc/ssap_report.html. Rotenone was selected as the mechanism of piscicide, and toxicity studies were conducted on a captive fish, resulting in mortality within 60 minutes at the lowest concentration (Lazur et al., 2006). After the treatment 8 adult and 834 juvenile northern snakeheads were recovered from the Crofton ponds (Lazur et al. 2006). Study results indicate that northern snakeheads are susceptible to normal doses of rotenone and that standard pond treatment techniques are effective in eradicating this invasive species (Lazur et al. 2006). The cost of this management effort was estimated at $110,000 (Courtenay and Williams, 2004).
Ridgebury Lake and Catlin Creek in New York State were treated with CFT Legumine (Rotenone) in order to eradicate C. argus argus. Temporary fish barriers were constructed along the creek to slow movement and partially block passage downstream. More than 220 snakehead fish were removed, most of which were juveniles (NYDEC, 2008). No confirmation of complete eradication in these waterbodies exists to date (W. Courtenay, USGS, USA, personal communication, 2010).
Local state biologists have decided not to attempt eradication of established populations, and rather, have decided to continue monitoring population levels and dispersal opportunities (Sea Grant Pennsylvania, 2012). A public education campaign was targeted towards anglers, commercial fishermen, and fisheries professionals to identify northern snakehead and provides a recommendation to kill and freeze suspected snakehead captures and notify the Pennsylvania Fish and Boat Commission (Sea Grant Pennsylvania, 2012).
Potomac River Basin (Potomac River)
The northern snakehead has become established in the Potomac River system and attempts at eradication and population control are being made by the states of Virginia and Maryland. The Virginia Department of Game and Inland Fisheries conducts periodic electro-fishing surveys (VDGIF, 2004). The use of passive gear, such as minnow traps, fyke nets, hoop nets etc., during the spring dispersal period may be an effective means of population control; however this has not yet been tested (N. Lapointe, Carleton University, Canada, personal communication, 2009).
ReferencesTop of page
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ContributorsTop of page
30/01/12 Updated by:
Bethany Schroeder, Fisheries and Oceans Canada, Centre of Expertise for Aquatic Risk Assessment, 867 Lakeshore Rd., Burlington, ON L7R 4A6, Canada
Becky Cudmore, Fisheries and Oceans Canada, Centre of Expertise for Aquatic Risk Assessment, 867 Lakeshore Rd., Burlington, ON L7R 4A6, Canada
School of Biological Sciences, Faculty of Science and Engineering, Flinders University, Room 128b, GPO Box 2100, Adelaide SA 5001, Australia
Top of page
- = Present, no further details
- = Evidence of pathogen
- = Widespread
- = Last reported
- = Localised
- = Presence unconfirmed
- = Confined and subject to quarantine
- = See regional map for distribution within the country
- = Occasional or few reports