Species Profile - Anguilla rostrata

Anguilla rostrata (Lesueur, 1817)

Common Name: American Eel

Synonyms and Other Names:

Anguille, black eel, bronze eel, glass eel, green eel, river eel, silver eel, yellow eel

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).


This map only depicts Great Lakes introductions. Click here for Great Lakes region collection information Click here for the national map

Great Lakes Nonindigenous Occurrences: In 1973, this species was stocked but failed to establish in Lake Mead on the Colorado River, near the Arizona border and in Nevada (Minckley 1973). More than one specimen has been since collected from an unspecified location in Arizona in 1994 (Rinne 1994). It was also stocked on several occasions in Sacramento and San Francisco bays, California, in the late 1800s, apparently with no evidence of survival (McCosker 1989, Shebley 1917, Smith 1896). Thirteen specimens were collected in the San Francisco area during the period from 1978 to 1984 (McCosker 1989, Williamson and Tabeta 1991). Specimens have been reported from the San Luis Valley, Conejos County, Colorado, where they escaped from an aquaculture facility (Zuckerman and Behnke 1986). Eels were stocked in the Calumet River south of Chicago, Illinois, in 1873 (Goode 1884, Milner 1874b). Anguilla rostrata was also reported as established in several localities in Indiana in 1945 (Gerking 1945). An 1873 stocking introduced the American eel to a river near Eaton, Michigan (Goode 1884, Milner 1874). This species was accidentally introduced into the Elkhorn River near Omaha, Nebraska, that same year, when a railroad car transporting East Coast fish to the West Coast lost its cargo to the river after a railroad bridge collapsed. An estimated 1,500 eels from Martha's Vineyard and 40,000 from the Hudson River were released into the Elkhorn (Smith 1896). In 2000, one American eel was collected in the Nolichucky River, North Carolina, but a population is not established (Shute and Etnier 2000). In the late 1800s, Ohio received transplants of hundreds of thousands of eels, which likely arrived through the Welland Canal (Trautman 1981). The American eel was stocked in Utah Lake and Salt Lake, Utah in the late 1800s, but it disappeared shortly thereafter (Popov and Low 1953, Sigler and Miller 1963). In 1873, A. rostrata was also stocked in the Fox River at Appleton, Wisconsin (Goode 1884, Milner 1874).

Great Lakes Occurrences (outside of native range)
First collected in Lake Superior from Alger County, Michigan at the mouth of Beaver Lake Creek, Pictured Rocks National Lakeshore in 1957. In 1970, a specimen was collected from the mouth of the Brule River in Douglas County, Wisconsin, and again in 1974 from Superior Harbor in Douglas County (Becker 1983). In 1978, an American eel was collected from the Blackhoof River in Carlton County, Minnesota, a tributary of the Nemadji River in the Lake Superior drainage (Cochran 1981). Although individuals have been observed in Lake Superior, the American eel is currently not believed to be established there (Mandrak 2009). Identified in 1935 in Port Washington, Ozaukee County, Wisconsin; collected from Green Bay at Red Banks in 1968 and again in 1974 from Green Bay at Pestigo Point in the Lake Michigan Basin. In 1977, this species was collected in Harrington Beach State Park, Ozaukee County, Wisconsin (Becker 1983). Eels have also been collected in Illinois and Indiana waters of Lake Michigan (Lee et al. 1980 et seq.) Earliest non-indigenous Great Lakes occurrence, collected in 1844 after traveling through the Welland Canal from Lake Ontario but did not become established (Trautman 1981). Collected from Maumee Bay, Lucas County, Ohio, in 1902 but again failed to establish (Trautman 1981). In 1977, the first established population was reported in Lake Erie, in Erie County, Pennsylvania after traveling through the Welland Canal (Busch et al. 1977). First collected in Lake Huron in 1957 from Goderich Harbor, Ontario in Canadian waters. A specimen was later collected in 1966 from Canadian waters in Macpherson Point near Underwood, ON. Again in 1973, this species was collected on three separate occasions in Canadian waters, including Nottawasaga Bay, the North Channel, and St. Mary’s River near Macdonald, ON. In 1990 and 2000, two more collections from the Canadian waters of Lake Huron took place near the mouth of the Sauble River (Royal Ontario Museum 2011). There are no reports of this species being established in the American waters of Lake Huron.

Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Anguilla rostrata are found here.

Full list of USGS occurrences

State/Province	First Observed	Last Observed	Total HUCs with observations†	HUCs with observations†
IL	1873	1873	1	Little Calumet-Galien
MI	1957	2000	2	Betsy-Chocolay; Lake Superior
MN	1978	1978	1	Beartrap-Nemadji
OH	1844	1986	4	Cedar-Portage; Cuyahoga; Lake Erie; Sandusky
PA	1977	1977	1	Lake Erie
WI	1873	2000	4	Beartrap-Nemadji; Lake Michigan; Lake Superior; Lower Fox

Table last updated 4/27/2024

† Populations may not be currently present.

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.

Great Lakes Impacts: There is little or no evidence to support that Anguilla rostrata has significant environmental impacts in the Great Lakes outside of its native range.
Realized:
American eels in Texas and South Carolina have been found to be infected with the Asian eel nematode Anguicolla crassus (Fries et al. 1996, M. Ray, Texas Parks and Wildlife Department, pers. comm.). This nematode was originally known only to infect the Japanese eel, Anguilla japonica, in Southeast Asia (Kuwahara et al. 1974). However, this parasite has spread into the European eel, A. anguilla, and is now present in most European countries with up to 100% infectivity in some areas (Kennedy and Fitch 1990, Neumann 1985, Paggi et al. 1982). It colonizes the eel’s swimbladder, causing retarded growth and maturation, and is fatal to a high percentage of infected individuals. It has also been found to infect fin fish, with unknown consequences (R. Ward, Texas Parks and Wildlife, pers. comm.). A. crassus was first reported in U.S. waters in 1993, when an infected eel was found in a Texas aquaculture facility (Fries et al. 1996, M. Ray, Texas Parks and Wildlife Department, pers. comm.). It is thought to have arrived in the U.S. from shipments of infected foreign European eels, and has now colonized much of the Atlantic coast from Florida to New York (Reid 2001).

Potential:
This parasite is not yet present in the Great Lakes or St. Lawrence River, and it is considered unlikely to become established in eel populations in those regions due to extended cold winter water temperatures (4-9°C or less) (Knopf et al. 1998). However, there is a chance of this parasite being transmitted to these waters when summer water temperatures are above 9°C (Reid 2001). Many other parasites are also capable of infecting American eels, including protozoans, trematodes, cestodes, acanthocephalans, and crustaceans (Hoffman 1967).

There is little or no evidence to support that Anguilla rostrata has significant socio-economic impacts in the Great Lakes outside of its native range.
Realized:
As this species is native to Lake Ontario, its spread into the upper Great Lakes is not expected to have any significant negative socio-economic impact. An active eel fishery is currently maintained in Ontario on the Lake Ontario/St. Lawrence River ecosystem, however, these populations are currently suffering decline, as are many other native eel populations (Reid 2001). It is unknown how expanded Anguilla rostrata populations throughout the rest of the Great Lakes will affect the Lake Ontario population, or whether expanded populations will become commercially valuable on their own. Recreational landings of American eel since 1981 have generally accounting for less than 1% of total eel landings for U.S. recreational harvest, and eel catches in recreational fisheries are usually incidental to other targeted species (Shepherd 2006).

There is little or no evidence to support that Anguilla rostrata has significant beneficial effects in the Great Lakes outside of its native range.
Realized:
Glass eels are a popular part of the diet in Europe and are a delicacy on the Asian market. Therefore, this young life phase was heavily harvested in the U.S. from the Chesapeake Bay and the Gulf of St. Lawrence and shipped to Asia up until the 1970s (USFWS 2006). Currently, Maine is the only U.S. state to maintain a commercial American eel fishery (USFWS 2006), and a commercially valuable fishery is also present in Ontario on the Lake Ontario/St. Lawrence River ecosystem as well (Reid 2001). These fishery populations, as well as most other native populations, are suffering recent severe declines (Reid 2001). It is unknown if any beneficial contribution will be had on the commercially valuable fishery population in Lake Ontario as a result of expanded American eel populations in the Great Lakes. It is also unknown whether these non-native populations will become commercially viable in the Great Lakes on their own if they continue to expand.

Remarks: Since 2005, A. rostrata has been classified as apparently secure in the United States (N4) (NatureServe 2010). However, throughout the United States as a whole, American eel populations have experienced a decline over the past few decades, likely due to habitat loss and alteration, barriers to migration, over-fishing, parasitism, and pollution (Haro et al. 2000). Juvenile recruitment in Lake Ontario experienced an 81-fold decline between the years of 1985 to 1992 (Castonguay et al. 1994). Declines in the northern range of the American eel population are especially significant, as northern sub-populations are thought to carry the highest reproductive potential (Casselman 2003).

Management: Regulations

The American eel is imperiled throughout its native range, including Lake Ontario. It is managed for preservation of the fishery and recovery of the native population by the Atlantic States Marine Fisheries Commission and the American Eel Task Group of the Great Lakes Fishery Commission. In the Great Lakes it is managed with “ the ultimate goal … the long-term sustainability of American Eel in Ontario throughout its historic range.” (MacGregor et al 2011). Although outside its native range, the American eel is considered a threatened species in Ohio (including Lake Erie) and managed with the goal of preserving the species in Ohio waters. American eels are rare in the upper Great Lakes, and generally managed for their potential to contribute to the downstream Lake Ontario populations (managed as threatened valuable species rather than invasive).

Control

Physical

The American eel is generally resident in tributaries to the Great Lakes and moves through the lakes on its journey to spawn in the Sargasso Sea (and juveniles back to the tributaries). Removal of dams blocking upstream migration into tributaries is key to the restoration of the species.

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 reference list)

Other Resources:
USGS/NAS Technical Species Profile

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

FishBase Summary

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

Contributing Agencies:

Revision Date: 9/12/2019

Peer Review Date: 2/5/2016

Citation for this information:
Fuller, P., L. Nico, M. Neilson, K. Dettloff, and R. Sturtevant, 2024, Anguilla rostrata (Lesueur, 1817): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/GreatLakes/FactSheet.aspx?Species_ID=310, Revision Date: 9/12/2019, Peer Review Date: 2/5/2016, Access Date: 4/27/2024

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.