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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: American Eel

Synonyms and Other Names: Anguille, black eel, bronze eel, glass eel, green eel, river eel, silver eel, yellow eel

Taxonomy: available through www.itis.gov

Identification: Elongated, snakelike body with a broad, depressed snout. Lower jaw extends beyond the upper jaw, and eyes are placed well forward on the head. The mouth is large and slightly oblique, with the gape extending to the posterior margin of the eye. One long dorsal fin originates far behind the pectorals and is continuous with the rounded caudal and anal fins. Pelvic fins are absent. One small gill slit is present in front of each pectoral fin. Scales are cycloid and embedded, and are difficult to see without magnification. The lateral line is well developed and prominent. Coloration varies depending on maturity level. The larval stage, known as the glass eel, is transparent and leaf shaped with a prominent black eye. This stage develops into an elver, which exhibits dark coloration from grayish green to brown. The first, sexually immature, adult stage has coloration ranging from yellow to olive-brown. Sexually mature adults have prominent black eyes and are dark brown to gray with a metallic sheen on their dorsal side and silver to white on their ventral side. During their spawning migration, coloration may transition from bronze to silver. As individuals mature, the eye develops a gold tinge known as “retinal gold” (Hardy 1978, Page and Burr 1991).

Males are reported to mature around 28 cm and females around 46 cm (Hardy 1978).

Size: 152 cm.

Native Range: Anguilla rostrata is a catadromous species that spawns in the Sargasso Sea of the Western Atlantic and ascends streams in North and South America to live its adult stage in freshwater (Lee 1980, Simon 1999, Smith 1997). Its range extends from Greenland south down the Atlantic coast of Canada (including Newfoundland) and the USA, and as far south as Panama and Brazil. It is common throughout the Caribbean and West Indies. The Mississippi River and the Lake Ontario basin comprise its native freshwater range in the United States (Page and Burr 1991, Scott and Crossman 1973). Niagara Falls forms the edge of its native distribution within the Great Lakes (COSEWIC 2006).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Native range data for this species provided in part by NatureServe

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: Anguilla rostrata is catadromous, spawning in saltwater and returning to freshwater lakes, streams, and rivers to live its adult life. It is also considered a panmictic species, with all species members randomly mating as a single breeding population (COSEWIC 2006). Spawning occurs in autumn after migration to the Sargasso Sea, where eels hatch from eggs and are carried to the Atlantic coast after about one year of drifting through currents. These post-larval eels spend most of their time on the bottom in close proximity to shelter, such as burrows, plant masses, snags, and tubes (COSEWIC 2006, Fahay 1978, Van den Avyle 1984). By the time they reach shore, the eels have developed into their yellow adult form, although they are not yet sexually mature. In this phase, they are nocturnal carnivores, feeding on insects, fish, fish eggs, crabs, worms, clams, frogs, and dead animal matter (Lookabauch and Angermeier 1992). Eel density tends to decrease with distance from the sea in medium and large rivers, and it is thought that eel density drives the determination of sex structure in estuarine rivers: where eels are more concentrated, there are more likely to be males, and where eels are less concentrated, there are more likely to be females (COSEWIC 2006, USFWS 2006). As the American eel grows, it experiences a shift in diet, moving from primarily small insects to larger prey such as fish and crustaceans by the time it reaches a length of 400 mm (Ogden 1970).

Anguilla rostrata is a nocturnal species, taking shelter during the daylight hours (Baras et al. 1998, Van Den Avyle 1984). As an adult, A. rostrata prefers to live in streams with continuous flow or in muddy, silt bottomed lakes. Here, it spends most of its time at the bottom in search of food (Scott and Scott 1988). While small eels tend to be found in faster flowing water, larger eels are associated with slow, deep, and muddy habitats (Fahay 1978, Meffe and Sheldon 1988, Van Den Avyle 1984). The American eel possesses the ability to breathe through its skin, allowing it to travel over land and move around barriers in streams. It can tolerate a wide range of temperatures between 4 and 25°C but is sensitive to low dissolved oxygen levels (Baensch and Riehl 1995, Hill 1969, Sheldon 1974).

After as few as three years (or for females, as many as 40 years) living in freshwater, the American eel reaches sexual maturity and is ready to return to the Sargasso Sea to spawn (Miller 2005). Each individual becomes able to reproduce when it reaches a mature size, regardless of age. Individuals who spend their life in freshwater will grow slower than those who live in brackish water, meaning freshwater individuals will take much longer to become sexually mature. To prepare for their journey back to the sea, the American eel undergoes a wide variety of physical changes. Its body pigmentation changes to have dark bronze to black dorsal sides with a silvery underside. Fat reserves increase, as well as the number of blood vessels feeding the swim bladder. Its eyes double in size and develop an increased sensitivity toward blue, giving the eel better vision in deep ocean water. Once back in the sea, females release between about 500,000 and 4,000,000 eggs, with large individuals (100 cm) capable of releasing up to 8,500,000 (Facey and Van den Avyle 1987). It is believed that the adult eels die after spawning occurs, as none have been observed migrating up rivers thereafter (Facey and Van den Avyle 1987).

Means of Introduction: Intentionally stocked in most locations; accidentally stocked in the Elkhorn River, Nebraska; escaped from an aquaculture facility in Colorado. Since 1874, there have been many shipments of A. rostrata from the eastern United States to California to stock rivers and for fish farming purposes (Williamson and Tabeta 1991). Eels caught in California waters during the 1970s and 1980s are believed to have been imported by Japanese or Chinese restaurants or by fish farms, and the eels either escaped or were released (McCosker 1989, Williamson and Tabeta 1991). In Texas and South Carolina, eels were intentionally introduced for aquaculture and subsequently escaped from the aquaculture facility.

The American eel is thought to have gained access to the upper Great Lakes through the Welland Canal, connecting lakes Ontario and Erie (COSEWIC 2006, Scott and Crossman 1973). The canal opened in 1829, and the first record of the Anguilla rostrata above Lake Ontario was from Lake Erie in 1844 (Trautman 1981). While on Lake Ontario, early captains of Great Lakes vessels commonly carried a tub of eels for food. These eels were frequently thrown overboard when the crew either tired of them or procured better fishes as the vessels sailed through the Great Lakes (Goode 1884). Several thousand eels were later stocked into rivers in Illinois draining into Lake Michigan and into a river near Eaton, Michigan, gaining access to the Great Lakes on multiple fronts (Goode 1884). From 1877-1891, over 2.2 million eels were stocked in Michigan (Fukano et al. 1964).

Status: Failed in Arizona, California, Colorado, Nevada, and Utah. Established in Lake Erie drainages of Pennsylvania and Ohio.

Great Lakes (outside of native range)
Anguilla rostrata is present but uncommon in the upper Great Lakes (Becker 1983). Populations of A. rostrata are currently established in Lake Erie (Busch et al. 1977) and have been collected on multiple occasions from Lakes Michigan, Huron, and Superior where their establishment is uncertain.

Impact of Introduction: Eels in Canada (New Brunswick and Nova Scotia), Connecticut, Florida, Maine, Maryland, Massachusetts, New Jersey, New York, Rhode Island, South Carolina, and Texas have been found to be infected with the Asian eel nematode Anguicolla crassus (Sokolowski and Dove, 2006; Aieta and Oliveira, 2009; M. Ray, personal communication). Infection rates of eels varies widely, with locations ranging from 0-76% prevalence and mean infection intensity ranging from 1.0-7.6 worms per eel (Barse and Secor, 1999; Aieta and Oliveira, 2009). This parasite infests the swimbladder (Sokolowski and Dove, 2006), causing retarded growth and maturation, and is fatal to a high percentage of eels. It has also been found to infect small fishes, amphibians, and aquatic insects, which are used as paratenic hosts. The nematode was originally known only in Japanese eels Anguilla japonica, and was likely transported to both Europe and North America through importation of Japanese eels for aquaculture feasability studies. Nematode populations in Europe and North America stem from separate introductions from Taiwan and Japan, respectively (Wielgoss et al., 2008).

Remarks: An adult eel was captured from the Sacramento-San Joaquin Delta, near Stockton, San Joaquin County, California, in 1964, but there is confusion surrounding its identity. The voucher specimen (SIO 64-219) is a skin only and was reported to be A. rostrata by Skinner (1971); however, the same specimen was reported as being either A. rostrata or A. anguilla by McCosker (1989), and as Anguilla sp. by Williamson and Tabeta (1991). Also see remarks under A. anguilla. Although not outside their native range, eels tentatively identified as this species have been used extensively for aquaculture in several areas, including Texas and South Carolina. The exact origin, and therefore positive identity of eels cultured in Texas has been somewhat uncertain. The Texas fish are believed to be native eels from the southeast coast, but there is a possibility that the fish actually may represent one of the foreign species, A. japonica or A. anguilla. Many of these eels escaped a southern Texas aquaculture facility into nearby Arroyo Colorado. In addition, before it was realized the eels from the Texas facility were infected with a parasite, Anguillicola crassus, live specimens were shipped to South Carolina (Ray, personal communication). Possibly escapees from South Carolina facilities, infected A. rostrata were captured later off the coast of South Carolina (Ray, personal communication). At least three American eels have been collected from Lake Superior on the Canadian side. These were likely ballast water introductions (Mandrak and Crossman 1992). Phelps et al. (2014) examined catch data of American eels in the upper Mississippi River, showing a decline in abundance over time. American eels are listed as endangered on the IUCN Red List (Jacoby et al. 2014).

Voucher specimens: California (CAS 41042-45, 62246, 44056, 53928, 62206), Colorado (MSB, uncataloged (LDZ-50, 51, 86)), Texas (Texas Parks and Wildlife, Palacios).

References: (click for full references)

Aieta, A.E., and K. Oliveira. 2009. Distribution, prevalence, and intensity of the swim bladder parasite Anguillicola crassus in New England and eastern Canada. Diseases of Aquatic Organisms 84:229-235. http://www.int-res.com/articles/dao2009/84/d084p229.pdf.

Atlantic States Marine Fisheries Commission.  2000.  Interstate Fishery Management Plan for American Eel: Fishery Management Report No. 36.  Prepared by the American Eel Plan Development Team And Approved by the Atlantic States Marine Fisheries Commission.  http://www.asmfc.org/uploads/file/amEelFMP.pdf

Baensch, H.A., and R. Riehl. 1995. Aquarien Atlas. Band 4. Mergus Verlag GmbH, Verlag für Natur- und Heimtierkunde, Melle, Germany. 864 p.

Baras, E., D. Jeandrain, B. Serouge, and J.C. Philippart. 1998. Seasonal variations in time and space utilization by radio-tagged yellow eels Anguilla anguilla (L.) in a small stream. Hydrobiologia 371-372: 187-198.

Barse, A.M., and D.H. Secor. 1999. An exotic nematode parasite of the American eel. Fisheries 24(2):6-10.

Becker, G.C. 1983. Fishes of Wisconsin. University of Wisconsin Press, Madison. 1052 pp.

Busch, W.N., D.H. Davies, and S.J. Nepszy. 1977. Establishment of white perch, Morone americana, in Lake Erie. Journal Fisheries Research Board Canada 34(7): 1039-1041.

Casselman, J.M. 2003. Dynamics of resources of the American eel, Anguilla rostrata: declining abundance in the 1990s. Chapter 18 pp. 255-274. In K. Aida, K. Tsukamoto, K. Yamauchi (editors). Eel Biology, Springer-Verlag Tokyo.

Casselman, J and D. Cairns [eds] 2009.  Eels at the Edge: Science, Status, and Conservation Concerns American Fisheries Society Symposium 58, American Fisheries Society, Bethesda, Maryland, 2009.

Castonguay, M., P.V. Hodson, C.M. Couillard, M.J. Eckersley, J.D. Dutil, and G. Verreault. 1994. Why is recruitment of the American eel, Anguilla rostrata, declining in the St. Lawrence River and Gulf? Canadian Journal of Fisheries Aquatic Science 51: 479-488.

Cochran, P.A. 1981. An unusually small American eel (Anguilla rostrata) from the Lake Superior drainage. Canadian Field-Naturalist 95: 97-98.

Cooper, E. L. 1983. Fishes of Pennsylvania. Pennsylvania State University Press, University Park, PA.

COSEWIC 2006. COSEWIC assessment and status report on the American eel Anguilla rostrata in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. x + 71 pp. (www.sararegistry.gc.ca/status/status_e.cfm).

Cudmore-Vokey, B. and E.J. Crossman. 2000. Checklists of the fish fauna of the Laurentian Great Lakes and their connecting channels. Can. MS Rpt. Fish. Aquat. Sci. 2500: v + 39p.

Facey, D.E., and M.J. van den Avyle. 1987. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates (North Atlantic) - American eel. U.S. Fish and Wildlife Service Biological Report 82 (11.74). U.S. Army Corps of Engineers, TR EL-82-4. 28 pp.

Fahay, M.P. 1978. Biological and fisheries data on American eel, Anguilla rostrata (LeSueur). United States National Oceanic and Atmospheric Administration Northeast Fisheries Center Sandy Hook Laboratory Technical Series Report 17.

Fries, L.T., D.L. Williams, and S.K. Johnson. 1996. Occurrence of Anguillicola crassus, an exotic parasitic swimbladder nematode of eels, in the southeastern United States. Transactions of the American Fisheries Society 125(5): 794–797.

Fukano, K.G., H. Gowing, M.J. Hansen, and L.N. Allison. 1964. Introduction of exotic fish into Michigan. Michigan Department of Conservation, Institute of Fisheries Research, Ann Arbor, MI.

Gerking, S. D. 1945. Distribution of the fishes of Indiana. Investigations of Indiana Lakes and Streams 3:1-137.

Goode, G.B. 1884-87. The fisheries and fishery industries of the United State. Washington, DC: Government Printing Office.

Hardy, Jr., J.D. 1978. Development of Fishes of the Mid-Atlantic Bight: An Atlas of Egg, Larval, and Juvenile Stages. Volume II – Anguillidae thorough Syngnathidae. Fish and Wildlife Service, U.S. Department of the Interior. 458 pp.

Haro, A., W. Richkus, K. Whalen, A. Hoar, W. Dieter Busch, S. Lary, T. Brush, and D. Dixon. 2000. Population decline of the American eel: implications for research and management. Fisheries 25(9): 7-16.

Hill, L.G. 1969. Reactions of the American eel to dissolved oxygen tensions. The Texas Journal of Science 20(4):305-313.

Hoffman, G.L. 1967. Parasites of North American freshwater fishes. University of California Press, Berkeley, CA.

Jacoby, D., J. Casselman, M. DeLucia, G.A. Hammerson, and M. Gollock. 2014. Anguilla rostrata. http://www.iucnredlist.org/details/191108/0. Created on 08/27/2014. Accessed on 10/13/2017.

Kennedy, C.R., and D.J. Fitch. 1990. Colonization, larval survival and epidemiology of the nematode Anguillicola crassus, parasitic in the eel, Anguilla anguilla, in Britain. Journal of Fish Biology 36:117-131.

Knopf, K., J. Würtz, B. Sures, and H. Taraschewski. 1998. Impact of low water temperature on the development of Anguillicola crassus in the final host Anguilla anguilla. Diseases of Aquatic Organisms 33:143-149.

Kuwahara, A., A. Niimi, and H. Itagaki. 1974. Studies on the nematode parasitic on the air bladder of eel. I. Description of Anguillicola crassa N. Sp. (Philometridae, Anguillicolidae). Japanese Journal of Parasitology 23:275-279.

Lee, D.S. 1980. Anguilla rostrata (Lesueur), American eel. pp. 59 in D. S. Lee, et al. Atlas of North American Freshwater Fishes. North Carolina State Museum of Natural History, Raleigh, i-r+854 pp.

Lookabaugh, P.S., and P.L. Angermeier. 1992. Diel patterns of American eel, Anguilla rostrata, in the James River Drainage, Virginia. Journal of Freshwater Ecology 7(4):425-431.

MacGregor, R., L. Greig, J.M. Dettmers, W.A. Allen, T. Haxton, J.M. Casselman, and L. McDermott.  2011.  American Eel in Ontario: Past and Present Abundance, Principles, Approaches, Biological Feasibility, and Importance of Recovery.  Version 5.1; February 2, 2011.

Mandrak, N.E. 2009. Fish fauna of Lake Superior: past, present, and future. Pages 645-663 in Munawar, M., and I.F. Munawar, eds. State of Lake Superior. Michigan State University Press. East Lansing, MI.

McCosker, J. E. 1989. Freshwater eels (family Anguillidae) in California: current conditions and future scenarios. California Fish and Game 75(1):4-10.

Minckley, W. L. 1973. Fishes of Arizona. Arizona Fish and Game Department. Sims Printing Company, Inc., Phoenix, AZ.

Meffe, G.K., and A.L. Sheldon. 1988. The influence of habitat structure on fish assemblage composition in southeastern blackwater streams. American Midland Naturalist 120(2):225-240.

Miller, R.R. 2005. Freshwater fishes of México. The University of Chicago Press. 490 p.

Milner, J.W. 1874. Report on the propagation of the shad (Alosa sapidissima) and its introduction into new waters by the U.S. Fish Commissioner in 1873. Part XIX Report of the Commissioner of Fish and Fisheries for 1872 and 1873: 419-451.

Minckley, W.L. 1973. Fishes of Arizona. Arizona Fish and Game Department. Sims Printing Company, Inc., Phoenix, AZ.

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Ogden, J.C. 1970. Relative abundance, food habits, and age of the American eel, Anguilla rostrata (LeSueur), in certain New Jersey streams. Transactions of the American Fisheries Society 99(1):54-59.

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Phelps, Q.E., J.W. Ridings, and D.P. Herzog. 2014. American Eel population characteristics in the upper Mississippi River. American Midland Naturalist 171:165-171. http://www.bioone.org/doi/abs/10.1674/0003-0031-171.1.165

Popov, B.H., and J.B. Low. 1953. Game, fur animal, and fish introductions into Utah. Misc. Publication No. 4. Utah State Department of Fish and Game, Salt Lake City, UT.

Ray, M. - Texas Parks and Wildlife Department. Austin, TX.

Reid, K. 2001. The decline of American eel (Anguilla rostrata) in the Lake Ontario/St. Lawrence River ecosystem: A modeling approach to identification of data gaps and research priorities. Great Lakes Fishery Commission. Ann Arbor, MI. 

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Skinner, J.E. 1971. Anguilla recorded from California. California Fish and Game 57(1):76-79.

Smith, H.M. 1896. A review of the history and results of the attempts to acclimatize fish and other water animals in the Pacific states. Pages 379-472 in Bulletin of the U.S. Fish Commission, Vol. XV, for 1895.

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Van den Avyle, M.J. 1984. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates (South Atlantic)- American eel. U.S. Fish and Wildlife Service FWS/OBS-82/11.24. U.S. Army Corps of Engineers, TR EL-82-4. 20 pp.

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Wielgoss, S., H. Taraschewski, A. Meyer, and T. Wirth. 2008. Population structure of the parasitic nematode Anguillicola crassus, an invader of declining North Atlantic eel stocks. Molecular Ecology 17:3478-3495.

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Zuckerman, L.D., and R.J. Behnke. 1986. Introduced fishes in the San Luis Valley, Colorado. Pages 435-452 in R. H. Stroud, ed. Fish culture in fisheries management. Proceedings of a symposium on the role of fish culture in fisheries management at Lake Ozark, MO, March 31-April 3, 1985. American Fisheries Society, Bethesda, MD.

Other Resources:
Distribution map in Illinois - ILNHS

US Fish and Wildlife Service

Great Lakes Waterlife

US Fish and Wildlife Service Ecological Risk Screening Summary for Anguilla rostrata

Author: Fuller, P., L. Nico, M. Neilson, K. Dettloff, and R. Sturtevant

Peer Review Date: 2/5/2016

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.