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| NAS - Nonindigenous Aquatic Species |
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Common Name: Asian swamp eel
Synonyms and Other Names: rice eel, ricefield eel, belut, rice paddy eel, ta-unagi. Other names used for this species include Monopterus alba, Fluta alba, and Monopterus javanenesis.
Taxonomy: available through 
Identification:
Distinguishing characteristics and illustrations or photographs were given by Day (1958), Sterba (1973), Rosen and Greenwood (1976), Masuda et al. (1984), Talwar and Jhingran (1992), and Kottelat et al. (1993); characteristics were also provided by Smith (1945) and Merrick and Schmida (1984). This eel was included in keys of Rosen and Greenwood (1976), Talwar and Jhingran (1992), and Kottelat et al. (1993).
Most individuals in Florida are olive-drab brown in color with yellow-orange bellies (as shown above). However, some specimens are brightly colored with variations of orange, pink, and a calico pattern (Shafland et al. 2010).
The taxonomy of the genus Monopterus is in need of systematic review. Monopterus albus was initially thought to be a single species, but subsequent study has shown four known populations of this "species" (in Florida and Georgia) may actually be three distinct species or taxa, each from a different area of Asia (Collins et al., 2002).
Size: 100 cm.
Native Range:
Asia, from northern India and Burma to China, perhaps Asiatic Russia, Japan, and the Indo-Malayan Archipelago (Bailey and Gans 1998); possibly northeastern Australia (Merrick and Schmida 1984).
Genetic analysis indicates that there have been multiple introductions from different geographic areas (Collins et al., 2002). The Atlanta population is from Japan or Korea; the populations in Tampa and North Miami are from Southern China; and the population in Homestead is from IndoChina, the Malay Peninsula, or the East Indies (Collins et al., 2002).
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Interactive maps: Continental US, Alaska, Hawaii, Caribbean
Nonindigenous Occurrences:
A synbranchid tentatively identified as this species was recently discovered in several waterways in peninsular Florida near Tampa, Homestead and Miami (Nico, unpublished data). It also is known from three spring-fed impoundments (Chattahoochee River drainage) at the Chattahoochee Nature Center in Roswell, Fulton County, and the Chattahoochee River National Recreation Area, Gwinnett County Georgia (Starnes et al. 1998; Tilmant 1999). This species was introduced to Oahu, Hawaii, before 1900 (Brock 1960; Maciolek 1984, Devick 1991a, 1991b). It is established on the island of Oahu (Mundy 2005). Swamp eels were also found in Silver Lake, Gibbsboro, New Jersey, in September 2008. (A different species was released in the Passaic River, New Jersey).
Ecology:
In their native range, Asian swamp eels consume a wide variety of invertebrate and vertebrate pray including fish (Yang et al. 1997, Cheng et al. 2003, Hill and Watson 2007). Hill and Watson's (2007) investigation into the diet of an introduced population near Tampa, Florida, revealed prey items such as amphipods, crayfish, fish, fish eggs, insects, oligochaetes, orgainic material. plant material and a tadpole. Shafland et al. (2010) found primarily fish (in 56% of stomachs), crustaceans (32%) (mostly crayfish), and insects (27%). Fish species included swamp darter (Etheostoma fusiforme), bluefin killifish (Lucania goodei), eastern mosquitofish (Gambusia holbrooki), other swamp eels, fat sleeper (Dormitator maculatus), largemouth bass (Micropterus salmoides), Mayan cichlid (Cichlasoma urophthalmus), tadpole madtom (Noturus gyrinus), bluegill (Lepomis macrochirus), jaguar guapote (Cichlasoma managuense), jewelfish (Hemichromis bimaculatus), black acara (Cichasoma bimaculatum), and spotted sunfish (Lepomis punctatus). Swamp eels had also eaten mollusks, frogs, a turtle, fish eggs, and a snake's head. The paper by Shafland et al. gives further details on size and frequency of prey items, as well as comparison of day and night feeding.
This species is unique in that all individuals are born as females and some later transform into males (Shafland et al. 2010). The population tends to be heavily skewed towards females (90-98%) in the populations studied in South Florida (Shafland et al. 2010). In Snake Creek, individuals transitioning ranged in size from 694-782 mm TL. Yet in another location, the smallest male was 434 mm TL. The smallest mature female was 318 mm TL and the smallest mature male was 434 mm TL.(Shafland et al. 2010).
A mature female averaged 439 (range 268-642) eggs (Shafland et al. 2010).
Laboratory studies show that swamp eels stopped feeding at 14-16 C and died at 8-9 C (Shafland et al. 2010). This temperature coincides with a range that would not extend farther north than Jacksonville (Shafland and Pestrak 1982). However, the Georgia population has survived air temperatures below freezing and ice cover over their pond habitat (Starnes et al. 1998) for many years indicating that it is different genetically (as found by Collins et al. 2002). Collins et al. (2002) predicted these ecological differences based on genetics.
This species is capable of breathing air, using atmospheric oxygen absorbed via a vascualarized breathing apparatus in the back of thier mouths (Shafland et al. 2010).
Means of Introduction:
Its introduction into Florida was probably the result of either an aquarium release or a fish farm escape or release, or a combination of all of the above (Nico, personal communication). The Tampa population is near an old fish farm. Colorful specimens may indicate selective breeding for the aquarium trade. They are known as a popular food item and may have been released. The release of another species of swamp eel in New Jersey was the result of a Buddhist prayer release of specimens purchased in a live fish market.
The eel was probably introduced into Georgia as an aquarium release. In Georgia, adults were first collected in 1996, although they were likely present since 1990 or before (Starnes et al. 1998).
It was presumably brought to Hawaii by Asian immigrants as a food fish (Devick 1991b). Brock (1960) stated that it was established in Hawaii prior to 1900. Devick (1991b) listed it as one of six fish species that were successfully introduced into Hawaii in the 19th century. However, Cobb (1902) and Jordan and Evermann (1902, 1905) made no mention of finding the species in their reports of their turn-of-the-century surveys of Hawaiian fishes.
Status:
Established in Florida (Shafland et al. 2010), Georgia (Starnes et al. 1998), and Hawaii (Devick 1991b). Status in New Jersey is unknown.
Impact of Introduction:
Largely unknown. Because they are generalized predators, this species is a potential threat to native fishes, frogs, and aquatic invertebrates. In both Georgia and Florida there is concern that the species will spread to adjacent water bodies. The Georgia impoundments where this eel has been taken are connected to the Chattahoochee River. However, Shafland et al (2010) state that in the 11 years they have studied this species in South Florida no deleterious ecological effects caused by swamp eels were noted.
Managment and Control
In theory, swamp eels can be controlled using rotenone. Although most small swamp eels were killed at concentrations of 2 and 4 mg/l, 100% mortality of swamp eels was only achieved at 8 mg/l (Schofield and Nico, 2007). In reality, the high concentration of rotenone needed, the habitat complexity in its current range in Florida, and the species behavior (burrowing and possibly crawling out of water) make success unlikely (Schofield and Nico, 2007).
Electrofishing has been tried as a method for controlling the population. Although it is very effective at catching swamp eels, it was determined that electrofishing alone was not enough to change the population structure of abundance. In addition many eels evaded capture by moving to deep water or by burrowing into the canal banks (Schofield and Nico, 2007).
Remarks:
Although there are reports of this species moving over land, (Shafland et al. 2010) found no evidence of that after studying them for many years. They are also reputed to be able to live out of water for a considerable length of time (Day 1958).
Georgia specimens were identified by Starnes.
Voucher specimens: Florida (UF uncatalogued); Hawaii (BPBM 3448, 3546, 5542, 5970, 28361, 30601, 30604, 33499; UF 98934); Georgia (UF 99872, USNM uncatalogued, NCSM).
Bryant, R. - Georgia Game and Fish, Atlanta, GA. 1994.
Cheng, H., Y. Guo, Q. Yu, and R. Zhou. 2003. The rice fieldeel as a model system forvertebrate sexual development.Cytogenetic and Genome Research 101:274–277.
Collins, T. M., J. C. Trexler, L. G. Nico, and T. A. Rawlings. 2002 . Genetic diversity in a morphologically conservative invasive taxon: Multiple introductions of swamp eels to the southeastern United States. Conservation Biology 16:1024-1035.
Day, F. 1958. The fishes of India; being a natural history of the fishes known to inhabit the seas and fresh waters of India, Burma, and Ceylon, volume I. William Dawson and Sons Ltd., London, England.
Devick, W. S. 1991a. Disturbances and fluctuations in the Wahiawa Reservoir ecosystem. Project F-14-R-15, Job 4, Study I. Division of Aquatic Resources, Hawaii Department of Land and Natural Resources. 21 pp.
Devick, W. S. 1991b. Patterns of introductions of aquatic organisms to Hawaiian freshwater habitats. Pages 189-213 in new directions in research, management and conservation of Hawaiian freshwater stream ecosystems. Proceedings of the 1990 symposium on freshwater stream biology and fisheries management, Division of Aquatic Resources, Hawaii Department of Land and Natural Resources.
Hill, J.E. and
Kottelat, M., A. J. Whitten, S. N. Kartikasari, and S. Wirjoatmodjo. 1993. Freshwater fishes of Western Indonesia and Sulawesi. Periplus Editions, Ltd., Republic of Indonesia. 221 pp. (+ plates).
Maciolek, J. A. 1984. Exotic fishes in Hawaii and other islands of Oceania. Pages 131-161 in W. R. Courtenay, Jr., and J. R. Stauffer, Jr., editors. Distribution, biology, and management of exotic fishes. The Johns Hopkins University Press, Baltimore, MD.
Masuda, H., K. Amaoka, C. Araga, T. Uyeno, and T. Yoshino, editors. 1984. The fishes of the Japanese Archipelago. Tokai University Press. Text: i-xxii + 437 pp.; atlas: pls. 1-370.
Merrick, J. R., and G. E. Schmida. 1984. Australian freshwater fishes: biology and management. Griffin Press, Netley, South Australia.
Roberts, T. R. 1989. The freshwater fishes of Western Borneo (Kalimantan Barat, Indonesia). Memoirs of the California Academy of Science 14. California Academy of Sciences, San Francisco, CA. 210 pp.
Schofield, P.J. and L.G. Nico. 2007. Toxicity of 5% rotenone to swamp eels. North American Journal of Fisheries Management 27:435-459.
Shafland, P.L., K.B. Gestring, and M.S. Sanford. 2010. An assessment of the Asian swamp eel (Monopterus albus) in Florida. Reviews in Fisheries Science 18(1):25-39.
Smith, H. M. 1945. The fresh-water fishes of Siam, or Thailand. Bulletin of the U.S. National Museum (Smithsonian Institution) 188:1-622.
Starnes, W. - North Carolina State Museum of Natural History, Raleigh, NC.
Sterba, G. 1973. Freshwater fishes of the world. English translation and revision from German. Two volumes. Tropical Fish Hobbyist Publications, Inc., Neptune City, NJ.
Talwar, P. K., and A. G. Jhingran, editors. 1992. Inland fishes of India and adjacent countries. A. A. Balkema, Rotterdam, The Netherlands. Two volumes.
Tilmant, J.T. 1999. Management of nonindigenous aquatic fish in the U.S. National Park System. National Park Service. 50 pp.
Yang, D., F. Chen, D. Li, and B. Liu. 1997. [Preliminary study on the food composition of mud eel, Monopterus albus.]Acta Hydrobiologica Sinica 21:24–30. (In Chinese with English abstract.)
Other Resources:
USGS Invasive Species Case File
Monopterus albus (Global Invasive Species Database)
Author: Pam Fuller and Leo Nico
Revision Date: 1/8/2010 Citation for this information:
Pam Fuller and Leo Nico. 2010. Monopterus albus. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=974> Revision Date: 1/8/2010
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