Asian swamp eel

{{Short description|Species of fish}} {{Distinguish|text=the rice-paddy eel (Pisodonophis boro)}} {{Speciesbox | image = Monopterus albus 2.jpg | status = LC | status_system = IUCN3.1 | status_ref = <ref name=IUCN>{{Cite iucn|author1=Ame, E.C.|author2=Ballad, E.L.|author3=Kesner-Reyes, K.|name-list-style=amp|year=2021|title=''Monopterus albus''|article-number=e.T166148A162163341|doi=10.2305/IUCN.UK.2021-2.RLTS.T166148A162163341.en|access-date=6 August 2023}}</ref> | taxon = Monopterus albus | authority = (Zuiew, 1793) | synonyms = *''Muraena alba'' Zuiew, 1793 *''Fluta alba'' (Zuiew, 1793) *''Synbranchus grammicus'' Cantor, 1842 *''Gymnotus albus'' Zuiew, 1789 *''Monopterus javanensis'' Lacepède, 1800 *''Unibranchapertura laevis'' Lacepède, 1803 *''Monopterus laevis'' (Lacepède, 1803) *''Ophicardia phayriana'' McClelland, 1844 *''Pneumabranchus cinereus'' McClelland, 1844 *''Monopterus cinereus'' (McClelland, 1844) *''Synbranchus xanthognathus'' Richardson, 1845 *''Monopterus xanthognathus'' (Richardson, 1845) *''Ophicardia xanthognatha'' (Richardson, 1845) *''Monopterus helvolus'' Richardson, 1846 *''Monopterus marmoratus'' Richardson, 1846 *''Apterigia saccogularis'' Basilewsky, 1855 *''Apterigia nigromaculata'' Basilewsky, 1855 *''Apterigia immaculata'' Basilewsky, 1855 | synonyms_ref = <ref name = FishBase/> }}

The '''Asian swamp eel''' ('''''Monopterus albus'''''), also known as '''rice eel''', '''ricefield eel''', '''rice paddy eel'''<ref name=Fuller/> or '''white rice-field eel''',<ref name=IUCN/> is a commercially important air-breathing species of fish in the family Synbranchidae. It occurs in East and Southeast Asia, where it is commonly sold and eaten throughout the region. It has been introduced to two areas near the Everglades in Florida and near Atlanta in Georgia.

==Taxonomy== The Asian swamp eel is a freshwater, eel-like fish belonging to the family Synbranchidae (swamp eels).<ref name=Nelson>Nelson, J.S. Fishes of the World. 3rd. New York City: John Wiley & Sons, Inc., 1994. Print.</ref>

Some work indicates that the species should be split into three geographical clades or cryptic species, although these were not given nomenclatural names, as the taxonomic synonymy was too complex to sort out at the time. The populations in the Ryukyus are distinct, the populations in China and Japan belong to another clade, and the rest, the original ''M. albus'', belong to the third group. Although these groups are too phenotypically similar to tell apart morphologically, they exhibit different brooding behaviours. In the Japanese/Chinese form, the males wait until the fertilised eggs hatch in their foam nests, and then keep the larvae in their mouths until they can breathe their own air. The Ryukyuan populations also make foam nests, but do not keep the larvae in the somewhat narrow buccal cavities in their mouths. The most widespread clade does not make foam nests, but lays the eggs among the roots of floating plants, and shows no parental care. Larvae use their pectoral fins to increase water flow and thus oxygen intake across their skin. This last form shows the most genetic diversity and may belong to numerous cryptic species. This form is also the type that has been introduced to the USA.<ref name=Matsumoto2009>{{cite journal |last1=Matsumoto |first1=Seiji |last2=Kon |first2=Takeshi |last3=Yamaguchi |first3=Motoomi |last4=Takeshima |first4=Hirohiko |date=19 August 2009 |title=Cryptic diversification of the swamp eel ''Monopterus albus'' in East and Southeast Asia, with special reference to the Ryukyuan populations |url=https://www.researchgate.net/publication/226719766 |journal=Ichthyological Research |volume=57 |issue=1 |pages=71–77 |doi=10.1007/s10228-009-0125-y |issn=1341-8998 |access-date=8 November 2020}}</ref>

''M. albus'' is not a "true" eel' in the order Anguilliformes; it belongs to the order Synbranchiformes.<ref>{{Cite journal |last1=Schoch |first1=Conrad L |last2=Ciufo |first2=Stacy |last3=Domrachev |first3=Mikhail |last4=Hotton |first4=Carol L |last5=Kannan |first5=Sivakumar |last6=Khovanskaya |first6=Rogneda |last7=Leipe |first7=Detlef |last8=Mcveigh |first8=Richard |last9=O'Neill |first9=Kathleen |last10=Robbertse |first10=Barbara |last11=Sharma |first11=Shobha |last12=Soussov |first12=Vladimir |last13=Sullivan |first13=John P |last14=Sun |first14=Lu |last15=Turner |first15=Seán |date=2020-01-01 |title=NCBI Taxonomy: a comprehensive update on curation, resources and tools |url=https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=43700 |journal=Database |language=en |volume=2020 |doi=10.1093/database/baaa062 |issn=1758-0463 |pmc=7408187 |pmid=32761142}}</ref>

==Description== [[File:Asian swamp eel (Monopterus albus) at a restaurant in Mindanao, Philippines 01.jpg|right|thumb|''Monopterus albus'' at a restaurant in Mindanao, the Philippines]] 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 swamp eel, it has a tapering tail and blunt snout, and lacks pectoral and pelvic fins. The dorsal, anal, and caudal fins are rudimentary, with the caudal fin often absent.<ref name=Nelson/> These fins serve to protect the swamp eel against rolling, and assist in sudden turns and stops. Its gill membranes are fused, but one v-shaped gill is located beneath the head. Such a shape prevents reverse flow.{{Citation needed|date=July 2021}}

Their colour is variable, but generally olive or brown, with irregular dark flecks.<ref name=Fuller>Fuller, P.L., L.G. Nico, and M. Cannister. ( 11 30 2010). [https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=974 "Asian swamp eel." Nonindigenous Aquatic Species]. United States Geological Survey. Retrieved 15 Mar 2011.</ref> Individuals in Florida usually have a dark body and head, with dark olive or brown dorsal coloring and light orange ventral coloring. Individuals caught in Florida can be more colourful, indicating breeding for the pet trade.<ref name=Fuller/><ref name="Shafland">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</ref>

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.<ref name=Fuller/>

===Similar species=== ''M. cuchia'', a related species also commonly eaten, has also been introduced to the USA. When it breaths, the throat expands on sides of head, as opposed to ventrally in ''M. albus''. This species also has "suprapharyngeal air chambers", which ''M. albus'' does not, and a few scales, which are entirely absent in ''M. albus''. ''M. cuchia'' has a single row of teeth, as opposed to two rows.<ref name=Fuller/>

==Distribution== It has a wide distribution.<ref>[http://el.erdc.usace.army.mil/ansrp/ANSIS/html/monopterus_albus_asian_swamp_eel.htm#Malbus_Distribution ''M.albus'' distribution] {{webarchive |url=https://web.archive.org/web/20110928170007/http://el.erdc.usace.army.mil/ansrp/ANSIS/html/monopterus_albus_asian_swamp_eel.htm#Malbus_Distribution |date=September 28, 2011 }}</ref> ''Monopterus albus'' is native to much of East and Southeast Asia, ranging west as far as India.<ref name=FishBase>{{FishBase| genus=Monopterus | species=albus | month=March | year=2019 }}</ref> ''M. albus'' is native to the tropical and subtropical areas of northern India and Burma to China, Japan, and Indo-Malayan Archipelago,<ref name=Fuller/> possible populations in Far East Russia and northeastern Australia might belong to different cryptic species.<ref name=Fuller/><ref name=Collins2002>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</ref> It is a common fish in India, Southern China to Malaysia and Indonesia.{{Citation needed|date=July 2021}}

The populations in most of Japan (Honshu and Kyushu) are likely introduced from China. The population in the Nara Basin was introduced from Korea in the beginning of the 20th century. Its distribution in Japan is discontinuous, which also indicates that it is introduced within the last millennium or so. The eels found in Taiwan appear to belong to two different species, a Japanese form was introduced in 1940, but a Southeast Asian form is also common and may have also been introduced or be native.<ref name=Matsumoto2009/> The eels were first introduced to the Oahu in Hawaiian Islands around 1900, where they still occur.<ref name=Fuller/><ref>{{cite journal|author=Clay, Keith|year=2003|title=Parasites Lost|journal=Nature|volume=421|issue=6923|pages=585–586|doi=10.1038/421585a|pmid=12571575|s2cid=1967346|doi-access=free}}</ref> Earliest record of the fish in the Philippines is in 1918 from a collection by the Commercial Museum of Philadelphia where it has become an invasive species.<ref>{{Cite journal |last=Fowler |first=Henry W. |date=1918 |title=A List of Philippine Fishes |journal=Copeia |issue=58 |pages=62–65 |jstor=1436970 |issn=0045-8511}}</ref><ref>{{Cite journal |last=Herre |first=Albert W.C.T. |date=August 1923 |title=A review of the eels of the Philippine archipelago |url=https://www.biodiversitylibrary.org/item/88959#page/143/mode/1up |journal=The Philippine Journal of Science |volume=23 |issue=2 |pages=125–126 |via=Biodiversity Library}}</ref><ref>{{Cite journal |last=Guerrero III |first=Rafael D. III |date=June 2014 |title=Impacts of Introduced Freshwater Fishes in the Philippines (1905-2013): A Review and Recommendations |url=https://philjournalsci.dost.gov.ph/images/pdf/pjs_pdf/vol143no1/pdf/impacts_of_introduced_freshwater_fishes_in_the_Phils.pdf |journal=Philippine Journal of Science |volume=143 |issue=1 |pages=49–59}}</ref>

Locations in the Southeastern United States were not colonized until the end of the 20th century.<ref name=Fuller/> Around 1990, the eels were introduced to several ponds at a nature center near Atlanta, Georgia, within the Chattahoochee River drainage basin; by 1994, individuals had migrated to an adjacent marsh, the Chattahoochee Nature Center north of Atlanta.<ref name=Reinert>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.</ref> Subsequently, eels were collected from Florida waters in 1997 at two widely separated areas, one in southeast and the other in west-central Florida.<ref name="Shafland"/> 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 eels have been discovered since 1993, one outside of Tampa, Florida, and one in southern Georgia near the Chattahoochee River.<ref name="Daerr">Daerr, Elizabeth G.(2000). [https://www.thefreelibrary.com/Asian+Swamp+Eel+Invades+Florida.-a062140589 "Asian swamp eel invades Florida."] National Parks. 74.5/6: 13–14.</ref> 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.<ref name=Fuller/>

==Ecology== ''M. albus'' is a nocturnal animal. Its diet includes other fish, shrimp, crayfish, frogs, turtle eggs, aquatic invertebrates such as worms and insects, and occasionally detritus.<ref name=Fuller/>

An old document from 1958 claimed ''M. albus'' is capable of moving over dry land, but many years of study found no evidence for this.<ref name=Fuller/><ref name="Shafland"/>

===Habitat=== [[File:Asian Swamp Eels (13145567903).jpg|thumb|right|Introduced Asian swamp eels in Georgia in the United States]] The preferred environment for the Asian swamp eel includes a wide variety of muddy, freshwater, shallow wetlands, such as rice paddies, ditches, ponds, marshes, streams, rivers, canals, lakes, and reservoirs. Depths less than 3 m are optimal. ''M. albus'' can live in a wide range of oxygen levels. This fish can obtain up to 25% oxygen from air transcutaneously if not using gills under water.<ref name=Fuller/>

===Lifecycle=== The Asian swamp eel is hermaphroditic. All young are females. As juvenile fish begin to mature, some take on the masculine phenotype. Males are capable of changing sex, allowing them to replenish female populations when female densities are low. This change from one sex to another can take up to a year.<ref>Talwar, P.K. [http://www.fishbase.org/Summary/SpeciesSummary.php?ID=4663&AT=asian+swamp+eel "Asian Swamp Eel."] ''FishBase.org''. Retrieved 13 Mar 2011.</ref>

Spawning can occur throughout the year.<ref name=Chivers1999>Chivers, C.J. (1999). "Swamp aka Rice Eels." Wildlife Conservation. 102.2: 18.</ref> Some Japanese and Chinese forms of ''M. albus'' exhibit a great deal of parental care. Large males construct bubble nests at the mouth of burrows and guard the eggs and young.<ref name=Fuller/><ref name=Matsumoto2009/> In some Japanese and Chinese forms, 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.<ref name=Matsumoto2009/><ref name=Chivers1999/>

===Disease=== Swamp eels are a host for the nematode ''Gnathostoma spinigerum''. In Thailand and Vietnam, eating raw or undercooked swamp eel is the most common cause of gnathostomiasis, an uncommon parasitic disease.<ref name="Setasuban1991">{{cite journal|author1=Setasuban P |author2=Nuamtanong S |author3=Rojanakittikoon V |author4=Yaemput S |author5=Dekumyoy P |author6=Akahane H |author7=Kojima S | title = Gnathostomiasis in Thailand: a survey on intermediate hosts of ''Gnathostoma'' spp. with special reference to a new type of larvae found in ''Fluta alba''. |journal=Southeast Asian Journal of Tropical Medicine and Public Health |year=1991 |volume=22 Supplement |pages=220–4 |pmid=1822890}}</ref><ref>{{cite journal|vauthors=Akahane H, Setasuban P, Nuamtanong S, Horiuchi S, Koga M, Kojima S |title=A new type of advanced third-stage larvae of the genus ''Gnathostoma'' in freshwater eels, ''Fluta alba'', from Nakhon Nayok, central Thailand |journal=Southeast Asian Journal of Tropical Medicine and Public Health |year=1995 |volume=26 |issue=4 |pages=743–7 |pmid=9139388}}</ref><ref name=Tran2009>{{cite journal|author1=Tran Phu Manh Sieu |author2=Tran Thi Kim Dung |author3=Nguyen Thi Quynh Nga |author4=Tran Vinh Hien |author5=Anders Dalsgaard |author6=Jitra Waikagul |author7=K. Darwin Murrell |title=Prevalence of ''Gnathostoma spinigerum'' infection in wild and cultured swamp eels in Vietnam |journal=Journal of Parasitology |year=2009 |volume=95 |issue=1 |pages=246–248 |doi=10.1645/GE-1586.1 |pmid=19245276 |s2cid=23748298}}</ref>

==Uses== thumb|Dish of rice with swamp eel in China The fish is an important protein source for people in Thailand.<ref name="Setasuban1991"/> It is cultured throughout Vietnam.<ref name=Tran2009/> In Indonesia, Cambodia, China, Laos, Myanmar, Thailand, Vietnam, and other Asian countries, swamp eels are farmed in polyculture rice fields and sold as a food product with the rice crop.{{Citation needed|date=July 2021}}

In Balinese, the eels are known as ''lindung'', they are sold dried in almost all village markets for use in Hindu offerings.<ref>{{cite web |url=https://dictionary.basabali.org/Lindung |title=Lindung |author= |website=BASAbali |date=29 March 2020 |access-date=8 November 2020}}</ref>

In Japan, it is known as ''ta-unagi'', from 田, pronounced "ta", meaning paddy and 鰻, pronounced "unagi", meaning eel, usually written in katakana as タウナギ, and not commonly eaten.<ref name="KDJ">1988, 国語大辞典（新装版） (Kokugo Dai Jiten, Revised Edition) (in Japanese), Tōkyō: Shogakukan</ref><ref name="DJR">2006, 大辞林 (Daijirin), Third Edition (in Japanese), Tōkyō: Sanseidō, {{ISBN|4-385-13905-9}}</ref><ref name="DJS">1995, 大辞泉 (Daijisen) (in Japanese), Tōkyō: Shogakukan, {{ISBN|4-09-501211-0}}</ref>

In addition to being useful as a food. This species of eel is also often released into natural water resources in Thailand. According to the belief of the Thai people that it will help to end suffering and sorrow, or as a merit as releasing other fish or other aquatic animals such as climbing perch (''Anabas testudineus''), striped snakehead (''Channa striata''), Chinese edible frog (''Hoplobatrachus rugulosus''), pond snail (''Filopaludina martensi'') etc.<ref>{{cite web|url=https://d.dailynews.co.th/article/783274/|work=Daily News|access-date=2023-06-10|date=2020-07-06|language=thai|title='แก้เคราะห์-เสริมดวงชะตา' แบบไหนถึงได้บุญ}}</ref>

==Conservation== Asian swamp eels might pose a future threat to the environment of Everglades National Park, although preliminary studies reported no deleterious ecological effects in Florida. However, more recent studies<ref name=Pintar>Pintar; M, Dorn, N; Kline, J; and Trexler, J. (2023) [https://doi.org/10.1016/j.scitotenv.2022.159245 Hydrology-mediated ecological function of a large wetland threatened by an invasive predator]. Science of the Total Environment, Vol. 857, part 1. 20 January 2023.</ref> in the Everglades do show several species faced precipitous declines after the introduction of swamp eels. Two crayfish became nearly absent from areas with swamp eels, and other species of fish also saw significant declines. The United States Geological Survey has used several methods to control the ''M. albus'' population here. They discourage catching and transporting the eel.<ref name=Fuller/> Water-management structures near established swamp eel populations are not being opened to prevent or at least retard dispersal, particularly into the waters of the park.<ref name=McPherson>McPherson, B.F., Miller, R.L., Haag, K.H., and Bradner, Anne. (2000) [https://pubs.water.usgs.gov/circ1207/ Water Quality in Southern Florida]. Florida,1996–98: U.S. Geological Survey Circular 1207, 32 p.</ref> Adult and juvenile swamp eels are 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 pesticide dilutions of antimycin-A were tested and found to be innocuous. No changes in morbidity and mortality were observed.<ref name=Reinert/> The fish in the United States likely originate from a different areas in Asia, and are slightly different in characteristics.<ref name=Collins2002/>

==References== {{Reflist}}

==External links== {{Commons category|Monopterus albus}} * {{FishBase family|family=Synbranchidae}} * [http://www.iucngisd.org/gisd/species.php?sc=446 Invasive Species Specialist Group] * [https://www.invasivespeciesinfo.gov/aquatic/fish-and-other-vertebrates/asian-swamp-eel Species Profile – Asian Swamp Eel (''Monopterus albus'')], National Invasive Species Information Center, United States National Agricultural Library * [https://el.erdc.dren.mil/ansrp/ANSIS/html/monopterus_albus_asian_swamp_eel.htm ''Monopterus albus''], US Army Corps of Engineers *[http://www.fishbase.org/PopDyn/KeyfactsSummary_1.php?ID=4663&GenusName=Monopterus&SpeciesName=albus&vStockCode=4880&fc=262 Life History Data on ''Monopterus albus'', Asian swamp eel]

{{DEFAULTSORT:Monopterus albus}} Asian swamp eel Category:Fish of Asia Category:Taxa named by Vasily Zuyev Category:Fish described in 1793