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Southeast Ecological Science Center
ASSOCIATED DISEASES AND PARASITES
Investigations of diseases and parasites of snakeheads concentrate on those species of importance in aquaculture. Hoffman and Schubert (1984) noted that most fishes can sometimes be hosts of parasites. Snakeheads are no exception.
Jinhui (1991) listed parasitic crustaceans of Channa argus, C. asiatica, and C. punctata from Chinese waters. A listing of known parasites of C. gachua, C. marulius, C. punctata, and C. striata from Bangladesh was provided by Arthus and Ahmed (2002). In that study, parasites of all but C. gachua equaled or far outnumbered the parasites reported by Bykhovskaya-Pavlovskaya and others (1964) for C. argus (table 2).
Literature on parasites of snakeheads includes numerous descriptions of new species, not detailed herein, but indicates that most studies concentrate on cultured fishes, such as Channa argus, C. punctata, and C. striata. Chiba and others (1989) noted that C. argus and C. maculata introduced parasites to Japan, but did not detail the parasites involved or fish species affected. None of the parasite literature we reviewed on snakeheads indicated that any of these represent a potential threat to native North American fishes. Conversely, such potential has not been examined.
A disease of snakeheads that has received broad attention is epizootic ulcerative syndrome (EUS), which causes high mortality in these fishes, particularly Channa striata and C. punctata under intensive culture. EUS involves several
Table 2-Parasites of northern snakehead (Channa argus) - click to enlarge
pathogens, including motile aeromonad bacteria (for example, Aeromonas hydrophila, A. caviae, Pseudomonas fluorescens; Prasad and others, 1998; Qureshi and others, 1999), a fungus, Aphanomyces invadans (considered a primary pathogen; Mohan and others, 1999; Miles and others, 2001), and perhaps a rhabdovirus (Kanchanakhan and others, 1999; Lio-Po and others, 2000). Another bacterium, Aquaspirillum sp., also has been implicated (Lio-Po and others, 2000). EUS may have originated in India in the 1980s, but has since been found in Pakistan, Thailand, and the Philippines, with outbreaks reported from all of these areas during the 1990s. Snakeheads are not the only fishes affected by this disease. It is also known to occur in airbreathing catfish (Clarias), the bagrid catfish genus Mystus, two cyprinid genera (Cyprinus and Puntius), mastacembelid eels (Mastacembelus), and the nandid genus Nandus in India (Mukherjee, 1998). In Thailand, it has been found in giant gourami (Osphronemus goramy) and climbing perch (Anabas testudineus) during an outbreak in 1996-1997 (Kanchanakhan and others, 1999).
A parasitic disease that can affect humans is gnathostomiasis, caused by a helminth parasite, Gnathostoma spinigerum. It has been recognized as a highly important disease with about 800 suspected cases per year in two hospitals in Bangkok, Thailand, between 1985 and 1988 (Setasuban, 1990). Channa striata has been identified as an intermediate host for this parasite, found mostly in muscle tissue and occurring in 100 percent of fish examined over 41 cm in length (Setasuban and others, 1991). It is unknown if additional species of snakeheads in Thailand and other countries of southeastern Asia may serve as an intermediate host for larvae of this parasite.
Most snakeheads are part of capture fisheries. Few details were found in the literature on fishing methods, but most appear to involve hook and line, traps, gillnets, or seines.
Species for which we have found no information that they are of importance as a fishery resource include Channa amphibeus, C. bankanensis, C. burmanica, C. cyanospilos, and C. melasoma. Some do not appear to be targets of active fisheries, but are believed or known to be periodically available in local markets as incidental catches. These species include C. aurantimaculata (Musikasinthorn, 2000), C. baramensis (Ng and others, 1996), C. barca (also in the aquarium trade; Talwar and Jhingran, 1992), C. bleheri (wild caught for the aquarium trade; Ralf Britz, personal commun., 2002), C. gachua (Talwar and Jhingran, 1992), C. harcourtbutleri (Ng and others, 1999), perhaps C. melanopterus, C. nox (Zhang and others 2002), C. panaw (Musikasinthorn, 1998), C. stewartii (Talwar and Jhingran, 1992), and possibly Parachanna africana and P. insignis. Those for which there are active commercial fisheries are C. argus (Berg, 1965; Baltz, 1991; Dukravets, 1992), C. asiatica (Nichols, 1943; Daiqin and others, 1999), C. lucius (for food and aquarium purposes; Ng and Lim, 1990), C. maculata (Nichols, 1943; Atkinson, 1977; Hay and Hodgkiss, 1981), C. marulioides (aquarium purposes; Ng and Lim, 1990), C. marulius (Sriramlu, 1979; Rao and Durve, 1989; Talwar and Jhingran, 1992), C. micropeltes (Lee and Ng, 1991; Dudley, 2000), C. orientalis (Rainboth, 1996), C. pleurophthalma (Lee and Ng, 1991; Kottelat and others, 1993; Dudley, 2000), C. punctata (Quayyum and Qasim, 1962; Bhuiyan and Rahman, 1984; Rao and Durve, 1989; also in aquarium trade, Talwar and Jhingran, 1992), C. stewartii (minor importance in India, also in aquarium trade; Talwar and Jhingran, 1992), C. striata (Roa and Durve, 1989; Talwar and Jhingran, 1992), and P. obscura (aquarium and food purposes; Dankwa and others, 1999) . In addition, C. argus, C. maculata, and C. striata are commercially fished in most areas where these species have been introduced. Interestingly, there are cultural differences in acceptance of using introduced C. argus as a food fish. Within its native range in China, Korea, and southern Siberia (Berg, 1965), and within its introduced range in Kazakhstan, Uzbekistan, and Turkemistan, it is considered a desirable and sought-after food fish (Baltz, 1991; Dukravets, 1992; FAO, 1994); nevertheless, it failed to become popular following its introduction to Japan in the early 1900s (Okada, 1960).
Snakeheads known to be cultured are summarized in table 3. The most important and widely cultured species appears to be Channa striata. This may apply, however, only within its native range and perhaps where it has been introduced into southern China. It is becoming evident that it has been misidentified in places where this species has been reported as introduced (Madagascar and Hawaii in particular), and the introduced snakehead is C. maculata (Ralf Britz, personal commun., 2002). Thus, the many reported introductions of C. striata to Pacific Islands summarized by Eldredge (1994) and Lever (1996) will require reexamination. Channa maculata is the second most important snakehead cultured in China (Fang Fang, personal commun., 2002), and its culture appears to be concentrated primarily in Guangdong Province, where it is native. During 2001, imports of snakeheads (likely C. maculata) into the U.S. increased, the point of export having been Ghangzhou, Guangdong Province. Until identification of introduced C. striata is verified, its reputation as the most widely cultured snakehead
Table 3-Species of the family Channidae currently known
remains in question. We have verified that it is in culture in Hawaii (Qin and Fast, 1996a,b,c; Qin and others, 1997; Qin, Fast, and Kai, 1997; Qin, He, and Fast, 1997; Qin and Fast, 1998; Pam Fuller, personal commun., 2002). Moreover, it is considered to be the most important species economically in India (Bhatt, 1970), and is being cultured there and in Thailand, Java (Hofstede and others, 1953); Vietnam (Pantulu, 1976; Bard, 1991); the Philippines (Conlu, 1986; Guerrero, 2000); Sri Lanka (Kilambi, 1986); Pakistan (Talwar and Jhingran, 1992); Malaysia (Ali, 1999); and Cambodia (Balzer and others, 2002).
Channa argus is the most important snakehead cultured in China (Fang Fang, personal commun., 2002) where it is grown in ponds, rice paddies, and reservoirs (Atkinson, 1977; Sifa and Senlin, 1995; Liu and others, 1998). It was being cultured on three fish farms in Arkansas until importation, culture, sale, and possession of snakeheads was prohibited by the Arkansas Fish and Game Commission in August 2002.
Channa micropeltes is cultured for food in Vietnam (Pantulu, 1976; Wee, 1982), Malaysia (Lee and Ng, 1991), Thailand (FAO, 1994), and Cambodia (Rainboth, 1996), and often in floating cages (Pantulu, 1976; Rainboth, 1996). Young of this species are sold in the aquarium fish trade where this species, at least in the U.S., has been the most available snakehead.
Channa marulius is cultured in ponds, ricefields, and irrigation wells that do not support other fishes in Pakistan and India (Bardach and others, 1972). Wee (1982) noted that it is reared in monoculture in India, where it is fed tilapia. Mirza and Bhatti (1993) contradicted Bardach and others (1972) in stating that this species is unsuitable for aquaculture in Pakistan due to its highly piscivorous nature. Young have been available in the aquarium fish trade and are presumed to have originated from cultured stock.
Channa punctata has been an important food fish in India, where it is fished commercially and reared in ponds (Quayyum and Qasim, 1962; Talwar and Jhingran, 1992). Some snakehead species, including C. punctata, used in intensive aquaculture, are subject to outbreaks of EUS, and this has been reported for this species in India (Prasad and others, 1998; Qureshi and others, 1999).
Parachanna obscura is being cultured in the Central African Republic (Micha, 1974), Ondo State, Nigeria (Ajana, 1983; Victor and Akpocha, 1992), Benin (Jackson, 1988), and Ghana (Morrice, 1991).
Locations where snakeheads have been introduced beyond their native ranges in the Eastern Hemisphere are shown in figure 3.
Channa argus - Reported as introduced into “Czecho-Slovakia” and Russia beginning in 1949 (Holcik, 1991). No specific localities of introduction or information on status of the releases were provided by Holcik (1991). Nina Bogutskaya (personal commun., 2002) reported early introductions that failed into the Volga delta and ponds in Ekaterinburg (formerly Sverdlovsk) Province in the southern Urals. An experimental introduction was made in ponds of Moscow Province during 1949-1950 that established. In 1953, it was recommended that the species be stocked widely, but that failed to happen. There was a report in a Russian aquarium journal in 1963 noting occurrence of this species in small lakes in the Podolsk Region, Moscow Province, but the species is presently absent from the Moscow area. Tandon (1976) reported that acclimatization experiments were conducted in the former Soviet Union after 1950, and that fry were collected from ponds near Moscow and the Ukraine in 1955 and sent to Czechoslovakia for acclimatization purposes. He concluded that the source of the original stock was the Amur basin.
Figure 3-Introductions of snakeheads in the Eastern Hemisphere. - click to enlarge
The northern snakehead was introduced into the Aral Sea basin in the early 1960s where it became established in the Amu Dar'ya, Syr Dar'ya, and Kashka-Dar'ya rivers of Kazakhstan, Turkmenistan, and Uzbekistan (Dukravets and Machulin, 1978; Usmanova, 1982; Guseva, 1990; Dukravets, 1992). The initial introduction was apparently accidental, with snakeheads mixed with shipments of Asian carps. All introductions were apparently from Yangtze basin stock (Salnikov, 1998), although some authors claim the stock came from the Amur basin and were purposeful releases to establish a food resource. Dukravets (1992) recorded additional introductions that became established in the Sarysu River, reservoirs on the Talus River, and Chu River of Kazakhstan during the 1980s. He also reported that 10 metric tons of northern snakeheads was harvested from reservoirs along the Talus River in 1989.
The northern snakehead was introduced from Korea in the early 1900s and became established in many waters of central and southern Japan (Okada, 1960; Nakamura, 1963; Uyeno and Akai, 1984), which includes the islands of Hokkaido, Honshu, Kyushu, and Shikoku (Hiroshi Ueda, personal commun., 2002).
Channa asiatica - Introduced and established in Taiwan (Musikasinthorn, 2000), probably released as a food resource.
Channa gachua - Ismail (1989), misidentifying this snakehead as C. orientalis (Ralf Britz, personal commun., 2003), included Kalimantan (southern Borneo) in the native range of this species, and Kottelat (1985) noted its presence in the Greater Sunda Islands of Indonesia (probably including Kalimantan). This may represent an introduction, but the rationale for introducing this very small snakehead is not apparent. Myers and Shapovalov (1932) recorded this species in Taiwan.
Channa maculata - Introduced and established as a food resource in Taiwan; Nara, Hyogo, Hiroshima, Mie, and Shiga prefectures, Japan; and the Philippines (Okada, 1960; Liang and others, 1962; Hay and Hodgkiss, 1981; Uyeno and Akai, 1984). Ralf Britz (personal commun., 2002) confirmed that it is this species, not C. striata, that is established in Madagascar. He has also identified this species as present in Oahu, Hawaii, since about 1900, based on specimens examined at the U.S. National Museum of Natural History.
Channa melasoma - Perhaps introduced and established in Palawan, Philippines (Kottelat, 1985). Pathway and rationale unknown.
Channa micropeltes - We believe the presence of the giant snakehead in Kerala State, southwestern India, and described by Day (1865a) as Ophiocephalus diplogramma was the result of an introduction from southeastern Asia that occurred prior to the mid-1800s.
Channa punctata - Smith (1950) reported this species as introduced in the vicinity of Delagoa Bay, southern Mozambique. Paul Skelton (personal commun., 2001) stated that no snakehead has been found or reported from southern Africa since the Smith (1950) record.
Channa striata - This species has been reported as the most widely introduced species of snakehead. It was recorded as introduced and established in Madagascar (Raminosoa, 1987; Reinthal and Stiassny, 1991; Stiassny and Raminosoa, 1994; Leveque, 1998), although Ralf Britz (personal commun., 2002) stated that this was a misidentification of C. maculata. The chevron snakehead is also recorded from the following locations, although some of these records may prove to be C. maculata, misidentified as C. striata: Mauritius (Parameswaran and Goorah, 1981; Welcomme, 1988, Lever, 1996); Philippines (Seale, 1908; Herre, 1924, 1934; Conlu, 1986); Vogelkop Peninsula, Papua, Indonesia (Allen, 1991); Sundaland, Sulawesi, Lesser Sundas, Moluccas (Welcomme, 1981; Kottellat and others, 1993; Lever, 1996). Kottelat and others (1993) reported introductions into China but gave no specific localities. Its presence in Papua, Indonesia, was confirmed through photographs supplied by Gerald L. Allen (personal commun., 2002). The species was also introduced into Fiji and New Caledonia where establishment is questionable, and its introduction to Guam failed (Maciolek, 1984). Channa striata is regarded as a prized food fish in many parts of southeastern Asia, and in some localities its oils are used to heal wounds and prevent scarring. Introductions beyond its native range were primarily to establish a live-food resource.
Five species of snakeheads have been reported from open waters of the United States (California, Florida, Hawaii, Maine, Maryland, Massachusetts, North Carolina, Rhode Island, and Wisconsin), and three became established as reproducing populations (fig. 4). One species was being cultured in Arksansas until possession of live snakeheads was prohibited in August 2002 and a fifth species is under culture in Hawaii.
A northern snakehead, Channa argus, was collected by California Department of Fish and Game personnel by electrofishing in a reservoir, Silverwood Lake, October 22, 1997. This represents the earliest known record of a live snakehead captured from open waters of the western United States. Silverwood Lake is in the Mohave River drainage, east-northeast of Los Angeles and north of San Bernardino in the San Bernardino Mountains, and receives water from the California Aqueduct. The specimen was subsequently frozen and, apparently, later discarded (Camm Swift, personal commun., 2002). A photograph of the 71 cm specimen that weighed 3.4 kg was taken, which allowed identification of the fish (John Sunada, personal commun. to Camm Swift, 2002). It remains unknown if the snakehead was released into Silverwood Lake or arrived through the California Aqueduct. The aqueduct has been the source of other fishes in the reservoir, including inland silverside (Menidia beryllina), striped bass (Morone saxatilis), bigscale logperch (Percina macrolepida), and tule perch (Hysterocarpus traskii) (Swift and others, 1993; Camm Swift, personal commun., 2002).
Figure 4-States where snakeheads have been collected from open waters,
An established population of the bullseye snakehead, Channa marulius, was discovered in residential lakes and adjoining canals in Tamarac, Broward County, Florida, in 2000 (Florida Fish and Wildlife Conservation Commission, 2001). It is unknown how long this species has occupied these waters, perhaps several years, but both juveniles and adults have been collected, indicating reproductive success. This species is a large snakehead with adults commonly reaching lengths of 120-122 cm (Talwar and Jhingran, 1992). In Maharashtra State, India, it can reach a length of 1.8 m and a weight of 30 kg, and was observed to reach a length of 30 cm in 1 year (Talwar and Jhingran, 1992).
The pathway for the introduction in Broward County, Florida, is unknown. The species may have been purposefully introduced to establish a food or aquarium fish resource or could have been released accidentally by aquarists, in which case several must have been released almost simultaneously. Because this species is considered as a game fish in its native range (http://www.fishingasia.com), it also could have been released illegally to establish a new sport fishing resource. Tamarac is located just east of Water Conservation Area II, north of Everglades National Park, and interconnected canal systems lead into this area. It is likely that Channa marulius will expand its range in peninsular Florida as its native range includes tropical to temperate climates. The bullseye snakehead is considered predacious (Jhingran, 1984; Talwar and Jhingran, 1992), especially on other fishes (Schmidt, 2001).
The northern snakehead, Channa argus, is also reported from Florida waters. Two individuals were caught in the St. Johns River below Lake Harney, Seminole and Volusia Counties in 2000, with unconfirmed reports of an additional three individuals caught nearby. An attempt to collect additional specimens by Florida Fish and Wildlife Conservation Commission (FFWCC) and U.S. Geological Survey (USGS) personnel by electroshocking in 2001 was unsuccessful, but will be repeated. Until reproduction has been confirmed, we consider the species as present but not established. This fish is not involved in the aquarium fish trade but has been sold in ethnic food markets as a food fish. The most likely pathway is introduction of livefood fish, perhaps to establish a local source.
A live northern snakehead was purchased in a live-food fish market in Orlando, Florida, in March 2002, another indication of its availability in a state where possession is illegal. Moreover, we found a few U.S. aquarium fish retailers that sell snakeheads via the Internet. Three species were purchased from a reputable dealer in Rhode Island who requested a copy of our permit to possess certain restricted fishes, including snakeheads. Private purchases can also be made through several Internet chat rooms where possession of permits is doubtlessly of no concern.
The blotched snakehead (Channa maculata), misidentified as the chevron snakehead (C. striata), has been established on Oahu, Hawaii, since the late 1800s, possibly introduced from southern China (Herre, 1924). For whatever reasons, it does not appear to have been introduced into other waters of Hawaii, although Morita (1981) reported the species from Kauai. It is now mainly confined to one or more reservoirs on Oahu (Maciolek, 1984). Ralf Britz (personal commun., 2002) has examined two specimens at the U.S. National Museum of Natural History, labeled as C. striata that were collected about 1900, and confirmed that they are C. maculata. We have examined other specimens, collected in the early 1900s on Oahu, borrowed from the American Museum of Natural History in New York City, Bernice P. Bishop Museum in Honolulu, the California Academy of Sciences in San Francisco, and the Field Museum of Natural History in Chicago, and they, too, are C. maculata. Two photographs, reported to be of C. striata in Yamamoto and Tagawa (2000) from Hawaii, are that of C. maculata. It was those photographs that alerted us to the likelihood that C. maculata existed in Hawaii. We believe that all past published records of C. striata in Hawaiian waters were based on misidentifications of C. maculata.
Channa striata is now being cultured as a food fish on Oahu, first imported in the early 1990s under permit to Arlo Fast of the University of Hawaii (Domingo Cravalho, Jr., personal commun. 2002). Peter Ng (personal commun., 2002) reported that he saw C. striata in a market in Honolulu in recent years. Pam Fuller (USGS, Gainesville, Florida) purchased five chevron snakeheads in Honolulu in September 2002. This species is regarded as carnivorous with a preference for other fishes (Mohsin and Ambak, 1983; Conlu, 1986), and was described as a “territorial ambush feeder” (Lee and Ng, 1991). Chevron snakeheads are used to control tilapia populations in culture ponds in the Philippines (Conlu, 1986; Milstein and Prein, 1993), and is one of the species of snakeheads capable of overland migration (Peter Ng., personal commun., 2002).
A northern snakehead, Channa argus, was caught by an angler in a 1.8-ha pond in Maryland on May 18, 2002 (Beth Rogers, personal commun., 2002). The angler, unable to identify the fish, took three photographs of the specimen before releasing it into the pond. Estimated total length of the specimen was 43-45 cm. On June 30, 2002, another angler captured a larger (66-67 cm) specimen from the same pond and dipnetted eight juveniles from the pond on the evenings of July 7-8. Maryland Department of Natural Resources personnel subsequently captured over 100 juveniles from the pond, proving that a well established population was present. When the pond was treated with rotenone (a pesticide used for fish management, as well as other uses) in August 2002, more than 1,200 northern snakeheads were recovered (Bob Lunsford and Steve Early, personal commun., 2002). In addition, at least three specimens of the giant snakehead, C. micropeltes, have been caught in Maryland waters in recent years (Bob Lunsford, personal commun., 2002). Presence of this subtropical/tropical species in Maryland waters where it could not overwinter likely resulted from releases by aquarists.
Maryland DNR fishery biologist Bob Lunsford examines a berm of sandbags and silt fences strategically placed to prevent pond water overflow or overland fish migration from Crofton Pond to the Little Patuxent River. Photo by Walter R. Courtenay, Jr., USGS. - click to enlarge
Biologists dipnetting for snakeheads. Photo by Tom Darden, Governors office, Annapolis, Maryland. - click to enlarge
New England States
A specimen of the northern snakehead, Channa argus, was collected in October 2001 from Newton Pond, Sudbury, Worcester County, Massachusetts, by Massachusetts Department of Fish and Wildlife personnel (Hartel and others, 2002). The likely source is live-food fish markets, as this species was the most common snakehead available in ethnic food markets and restaurants as a live-food fish. Moreover, it is capable of establishment in most freshwaters of the United States. Okada (1960) reported adults as voracious feeders, particularly on other fishes.
Specimens of the giant snakehead, Channa micropeltes, have been collected from open waters in Maine, Massachusetts, and Rhode Island (Courtenay and others, 1984; Fuller and others, 1999). This tropical/subtropical species could not establish itself in those temperate waters (Hartel and others, 2002). Juveniles of the species are cardinal red with two dark stripes on either side of the body, and are sold by aquarium fish retailers as red or redline snakeheads. Aquarist-oriented websites note that this species requires much animal food and that growth is rapid. These sites often advise that once these fish reach about 15-20 cm in length, no more than one individual should be kept in a single aquarium because they are aggressive predators. The pathway for release into these New England States was likely aquarists when their “pets” grew too large for their aquaria and/or because of the costs of feeding them. Releases of this species into subtropical waters in southern Florida or Hawaii could lead to establishment of this snakehead, regarded as the most predacious channid and known to have attacked humans (Ng and Lim, 1990; Lee and Ng, 1991; Kottelat and others, 1993).
An angler reported having caught two blotched snakeheads, Channa maculata, from a bridge over the Charles River in Boston in late July 2002 (Karsten Hartel, personal commun., 2002). We confirmed that two live snakeheads purchased in an ethnic market in Boston in October 2001 by Karsten Hartel were C. maculata, thus proving local availability of this species at that time.
On July 31, 2002, two anglers reported catching two northern snakeheads from Lake Wylie, a reservoir on the Catawba River, Mecklenburg County, North Carolina (Wayne Starnes, personal commun., 2002). North Carolina Wildlife Resources Commission biologists sampled the lake using electrofishing equipment on August 14, 2002, but failed to find any snakeheads (Russell Wong, personal commun., 2002).
A single specimen of the giant snakehead, Channa micropeltes, was captured by personnel of the Wisconsin Department of Natural Resources in the Rock River near Beloit on September 4, 2003 (Karl J. Scheidegger, personal commun., 2003). This species would not overwinter in Wisconsin and was undoubtedly released by an aquarist.
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