Monopterus albus (common names: swamp eel, rice eel, white ricefield eel, Asian swamp eel) (Synonym: Fluta alba (Bloch and Schneider, 1801)) is an important air-breathing commercial species of fish in the Synbranchidae family. Originating in the waters of East and Southeast Asia, it has been identified as an invasive species in the North American Everglades.
Taxonomy and Evolution
The Asian swamp eel is a freshwater eel-like fish belonging to the family Synbranchidae. This family is native to the fresh, brackish, tropical, and subtropical waters of Asia, but is now present in West Africa and North, Central and South America. Its taxonomy, however, is incorrect. Though Monopterus albus was initially thought to be a single species, four known populations of the “species” in the southeastern United States may actually be three distinct species or taxa, each originating from a different area in Asia.Monopterus albus comes from the class or subclass Actinopterygii. It arose from the Osteichthyes, the first bony fish, whose fossil record dates back to the Triassic period. In turn, the bony fish came from the Acanthodii class of bony and cartilaginous fish. The common name of M. albus is somewhat of a misnomer, as the Asian swamp eel is not an eel, per se. Eels are of the order Anguilliformes, while M. albus is of the order Synbranchiformes.
The Asian swamp eel has a scaleless, anguilliform body that grows to a meter or less, typically 25 to 40 cm as an adult. As a Synbranchidae, it has a tapering tail, blunt snout, and lacks pectoral and pelvic fins. The dorsal, anal, and caudal fins are rudimentary, with the caudal fin often absent. These fins serve to protect the swamp eel against rolling, and assist in sudden turns and stops (link). Its gill membranes are fused, but one v-shaped gill is located beneath the head. Such a shape prevents reverse flow (link). Its body and head are dark, with dark olive or brown dorsal coloring and light orange ventral coloring. This coloration camouflages the aquatic predator; however, some are brightly colored with yellow, black and gold spots(link). The bristle-like teeth of the M. albus, which are not easily seen, also indicate its carnivorous behavior (link).
Monopterus albus has a scaleless cylindrical snake-like body with tapered tail and small eyes. It grows to a meter or less, usually 25 to 40 cm as an adult. Its body color is brown or green-brown above and white or light-brown below. In adults, paired fins are lacking, and the dorsal, caudal and anal fins are reduced. Through its life, Monopterus Albus develops a small top fin near its rear. The gill openings are merged into a single slit underneath the head while the mouth is large and protractile and both upper and lower jaws have tiny teeth for eating fishes, worms, crustaceans, and other small aquatic animals at night.
Life History M. albus is an evasive nocturnal animal (Source). Its diet includes other fish, shrimp, crayfish, frogs, turtle eggs, aquatic invertebrates like worms and insects, and occasionally detritus. Unlike the traits of its diurnal counterparts, M. albus life history traits (e.g. absolute density and survival) are difficult to accurately measure and can require decades of data to detect trends, as expressed by the lack of data available on the topic. This results in an increase in the population of the invasive species without adequate time for population control methods.
The Asian swamp eel has versatile motility and is even capable of moving over dry land for short distances. This behavior is used for relocation according to resource availability. In the absence of water and food, the Asian swamp eel is able to survive long periods of drought by burrowing in moist earth(link). If its home becomes unsuitable, M. albus simply crawls ashore and makes its way to a more suitable home by slithering over the land in a snake-like fashion. These characteristics enhance the ability of M. albus to disperse widely. The swamp eel is a voracious general predator, making it a threat to native fishes, amphibians, and aquatic invertebrates.
The survivorship of a species or cohort can be found by calculating the number or proportion of individuals surviving at each age. Type I survivorship is characterized by high survival in early and middle life, followed by a rapid decline in survivorship in later life because of physiological changes. Type II survivorship exhibits a constant mortality rate regardless of age because of consistent environmental threats.M. albus survivorship falls between Type I, physiological, and Type II, ecological. They exhibit a great deal of parental care, indicative of physiological survivorship. Large males construct bubble nests at the mouth of burrows and guard the eggs and young. Additionally, eel populations are dependant upon resource abundance, making their survivorship partially ecological. Because of the aforesaid behaviors, removal of the invasive species might be best achieved in the juvenile stage or immediately after spawning, when parental care is at its highest.
The Asian swamp eel is hermaphroditic. All young are females. As juvenile fish begin to mature, some take on the masculine phenotype. Males have transgendered capabilities, allowing them to replenish female populations when female densities are low. This change from one sex to another can take up to a year.
Spawning can occur throughout the year. Eggs are laid in bubble nests located in shallow waters. These bubble nests float at the water’s surface and are not attached to aquatic vegetation. Females produce up to 1,000 eggs, each, per spawning event. This characteristic is important when considering control of the invasive species. The greater the proportion of females in the population, the greater the amount of reproduction. Thus, it would be best to implement removal of the species at the juvenile stage of life cycle to obtain the largest number of the reproductive population.
Distribution and habitat
M. albus is native to the tropical and subtropical areas of northern India and Burma to China, Asiatic Russia, Japan, and Indo-Malayan Archipelago. It is one of the common fish found mainly in Asia, from India, Southern China to Malaysia and Indonesia. The fish is an important protein source for people in the northeastern part of Thailand. In Asia, the swamp eel is wide-ranging, occurring in both tropical and temperate climates. Endemic to southern and eastern Asia, swamp eels live in ditches, ponds, streams, and rice paddies.
The preferred environment for the Asian swamp eel includes a wide variety of freshwater-like shallow wetlands, stagnant waters, marshes, streams, rivers, ditches, canals, lakes, reservoirs, and ponds. While they prefer freshwater, they are also able to tolerate brackish and saline conditions, as seen in their colonization of American marshlands. Depths of less than 3 m are optimal. M. albus also easily tolerates cold temperatures—well below 0 degrees C-- and a wide range of oxygen levels. This fish can obtain up to 25% oxygen from air cutaneously if not using gills underwater. This means that factors that typically limit dispersal—temperature, oxygen, and salinity—do not limit the Asian swamp eel.
The Asian swamp eels were first introduced to the Hawaiian islands around 1900. Locations in the southeastern United States were not colonized until the end of the 20th century. As early as 1990, Asian swamp eels were introduced to several ponds at a nature center near Atlanta, Georgia, within the Chattahoochee River drainage basin; individuals have since migrated to an adjacent marsh of the Chattahoochee River. As a general predator, the Asian swamp eel has disrupted the ecological balance of the Everglades. In 1994, eel specimen were collected in ponds at the Chattahoochee Nature Center north of Atlanta, Georgia. Subsequently, eels were collected from Florida waters in 1997 at two widely separated areas: one in southeast and the other in west-central Florida. Tens of thousands of swamp eels are estimated to inhabit nearly 55 miles of two water canal systems in southern Florida, one in the North Miami area and another on the eastern side of Everglades National Park. Two other populations of the eel have been discovered since 1993: one outside of Tampa, Florida, and one in southern Georgia near the Chattahoochee River. One or more of the populations are believed to be the result of an intentional or accidental release of the creature from a home aquarium or fish farm. Some populations may have been the result of an attempt by a few local residents to establish the eels as a food source. Asian swamp eels pose a threat to the homeostasis of Everglades National Park  by disrupting the natural interactions between native species and their environment. The species has an incredible ability to survive in adverse conditions, and the Everglade food web presents no known natural predators. Swamp eels survive even in the dry season when other nonnative species normally die. To combat Asian swamp eel resilience, the American Fisheries Society is investigating methods for control, containment, and possible eradication.
The United States Geological Survey (USGS) proposed and implemented several methods in controlling the Monopterus albus population in Southern Florida. Having documented eel distribution, behavior, and biology, the USGS discourages catching and transporting the eel for use as bait, food, or aquarium pets. Water management practices are also changing to combat the invasive species. Selected water-control structures near established swamp eel populations are not being opened to prevent or at least retard dispersal, particularly into the waters of Everglades National Park. Adult and juvenile swamp eels are obligate air-breathers, while young absorb oxygen directly through the skin. As such, standard fish poisons or piscicides (e.g., rotenone and antimycin-A) that are transmitted across the gill membrane may not be effective. Serial piscicide dilutions of antimycin-A were tested and found to be innocuous. No change in morbidity and mortality were observed.
In China, Taiwan, Vietnam, and many other Asian countries, swamp eels are served as cuisine.
Swamp eels are an important host for Gnathostoma spinigerum. Eating raw or undercooked swamp eel can cause gnathostomiasis, an important disease in Thailand, Laos, Burma and Vietnam.  Neurognathostomiasis has been reported in the US, but a link to imported swamp eels has not been proven.
Gnathostoma binucleatum (which is native to the Americas) has not been previous been reported to cause neurognathostomiasis, suggesting that G. spinigerum has been introduced to the Americas, but a survey of Gnathostoma isolates has not confirmed this.
Sources and notes
- Nelson, J.S. Fishes of the World. 3rd. New York City: John Wiley & Sons, Inc., 1994. Print.
- Fuller, P.L., L.G. Nico, and M. Cannister. "Asian swamp eel." Nonindigenous Aquatic Species. United States Geological Survey, 11 30 2010. Web. 15 Mar 2011. <http://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=974>.
- Collins, Timothy M., Joel C. Trexler, Leo G. Nico, and Timothy A. Rawlings (2002). "Genetic Diversity in a Morphologically Conservative Invasive Taxon: Multiple Introductions of Swamp Eels to the Southeastern United States." Conservation Biology. 16.4: 1024-1035. Print.
- Zweig, Christa, and Frank Mazzotti. "Body Condition Analysis ...for Use in Everglades Restoration." Joint Conference on the Science and Restoration of the Greater Everglades and Florida Bay Ecosystem. Greater Everglades Ecosystem Restoration. University of Florida, Palm Harbor, FL. 13 Apr 2003. Keynote.
- McPherson, B.F., Miller, R.L., Haag, K.H., and Bradner, Anne, 2000, Water Quality in Southern Florida Florida,1996–98: U.S. Geological Survey Circular 1207, 32 p., on-line at http://pubs.water.usgs.gov/circ1207/
- Campbell, Neil A.; Reece, Jane B. (2005). Biology. Benjamin Cummings. pp. 1177 pp. ISBN 0-8053-7146-X.
- Talwar, P.K. "Asian Swamp Eel." FishBase.org. Academia Sinica. Web. 13 Mar 2011. <http://www.fishbase.org/Summary/SpeciesSummary.php?ID=4663&AT=asian+swamp+eel>
- Chivers, C.J. (1999). “Swamp aka Rice Eels.” Wildlife Conservation. 102.2: 18.
- Clay, Keith (2003). "Parasites Lost." Nature. 421: 585-586. Print.
- Reinert, T. R., C. A. Straight, et al. (2006). "Effectiveness of atimycin-A as a toxicant for control of invasive Asian swamp eels." North American Journal of Fisheries Management 26(4): 949-952.
- Shafland, Paul L., Kelly B. Gestring, and Murray S. Stanford (2010). "An Assessment of the Asian Swamp Eel (Monopterus albus) in Florida." Reviews in Fisheries Science. 18.1: 25-39. Print.
- Daerr, Elizabeth G.(2000). “Asian swamp eel invades Florida.” National Parks. 74.5/6: 13-14.
- Setasuban P, Nuamtanong S, Rojanakittikoon V, Yaemput S, Dekumyoy P, Akahane H, Kojima S. (1991). "Gnathostomiasis in Thailand: a survey on intermediate hosts of Gnathostoma spp. with special reference to a new type of larvae found in Fluta alba.". Southeast Asian J Trop Med Public Health. 22 Suppl: 220–4. PMID 1822890.
- Akahane H, Setasuban P, Nuamtanong S, Horiuchi S, Koga M, Kojima S (1995). "A new type of advanced third-stage larvae of the genus Gnathostoma in freshwater eels, Fluta alba, from Nakhon Nayok, central Thailand.". Southeast Asian J Trop Med Public Health 26 (4): 743–7. PMID 9139388.
- Tran Phu Manh Sieu, Tran Thi Kim Dung, Nguyen Thi Quynh Nga, Tran Vinh Hien, Anders Dalsgaard, Jitra Waikagul and K. Darwin Murrell (2009). "Prevalence of Gnathostoma spinigerum Infection in wild and cultured swamp eels in Vietnam.". Journal of Parasitology 95 (1): 246–248. doi:10.1645/GE-1586.1. PMID 19245276.
- Catalano M, Kaswan D, Levi MH (2009). "Wider range for parasites that cause eosinophilic meningitis". Clin Infect Dis 49 (8): 1283. doi:10.1086/605687. PMID 19780663.
- Almeyda-Artigas RJ, Bargues MD, Mas-Coma S (2000). "ITS-2 rDNA sequencing of Gnathostoma species (nematoda) and elucidation of the species causing human gnathostomiasis in the Americas". J Parasitol 86 (3): 537–544. doi:10.1645/0022-3395(2000)086[0537:IRSOGS]2.0.CO;2.
|Wikimedia Commons has media related to: Monopterus albus|
- Species Profile- Asian Swamp Eel (Monopterus albus), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Asian Swamp Eel.
- , US Army Corps of Engineers, responsible for investigating, developing and maintaining the nation's water and related environmental resources.
- , Life History Data.