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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: European eel

Synonyms and Other Names: Muraena anguilla (original combination), common names include Common eel, River eel, Glass eel, Silver eel, Weed eel

Taxonomy: available through www.itis.gov

Identification: The body is elongate, cylindrical with small, slit-like gill openings.  One pair of pectoral fins, no pelvic fins.  No spines in the anal or dorsal fins.  Vertebrae count 110-120.  The lower jaw is slightly longer than the upper.  The dorsal and anal fins are confluent around the caudal, generally with >500 soft rays.  Berg (1964) gave the following fin-ray counts:  243-275 dorsal rays, 175-249 anal rays, 15-21 pectoral rays.  Dorsal fin origin well behind pectoral fins.  Anal fin origin slightly behind anus; well back from origin of dorsal fin.  May attain 1.5 m. 

McCosker (1989) presents a key to five Anguilla species most likely to be imported to the United States. Also see Maitland (1977) and Wheeler (1978).

Size: to 1.5 m

Native Range: Atlantic Ocean:  Atlantic coast from Scandinavia to Morocco and rivers of North Atlantic, Baltic and Mediterranean seas.  Along the coast of Europe from the Black Sea to the White Sea.  Spawning area in western Atlantic (Sargasso Sea; Froese and Pauly 2005). 

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

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

Ecology: European eels are nocturnal, finding hiding places or burrowing into mud (or under stones) during the day and coming out in search of food at dusk. The cold months are spent in hibernation (Reshetnikov 2003; Froese and Pauly 2005).  Eels are remarkably mobile, and are capable of movement over dams, weirs and even land (McCosker 1989).

The diet is broad, and includes marine, estuarine and freshwater fauna.  The principal food is invertebrates (esp. molluscs and crustaceans) and fishes (Sinha and Jones 1975; Maitland 1977).  Eels also scavenge on dead fishes (Coad 2005).  Small eels feed on insect larvae, molluscs, worms, and crustaceans.  The diet of larger specimens consists predominately of other fishes.  European eels do not feed during the cold months (Reshetnikov 2003).  The species is reported to leave the water and enter fields to feed on terrestrial fauna, such as slugs and worms (Deedler 1970; Coad 2005).

McCosker (1989) noted that European eels can survive near freezing temperatures.  Deedler (1970) gave a range of roughly 0 – 30 ºC for survival. 

Anguillid eels are catadromous, spending their adult lives in freshwater or estuarine habitats, then migrating to the ocean (sometimes over long distances) to reproduce.  The leaf-shaped larvae common to all anguillids (called a leptocephalus) is especially suited to long distance migration.  The larvae drift in the plankton for an average of 7-11 months; however, this stage may last as long as three years (Maitland 1977).  Just before reaching coastal waters, the leptocephalus undergoes a metamorphosis into the "glass eel" stage that results in a shortening of the body and formation into a more cylindrical shape (Sinha and Jones 1975).  The glass eels gain pigmentation, transform into elvers and move into freshwaters.  During this life stage (e.g. in freshwater), the fish are known as "yellow eels" (Sinha and Jones 1975).  Eels are stimulated to move upstream toward lower temperatures and salinities (Tosi et al. 1986; Vollestad et al. 1986).  Eels may also migrate more readily when influenced by population pressure in the lower reaches of rivers (Moriarty 1986).  After migration to brackish or fresh waters, eels feed and grow (males for 6-12 years; females for 9-20 years) before returning to sea for reproduction (Froese and Pauly 2005).  Eels are called "silver" eels when migrating from freshwaters to the sea (Sinha and Jones 1975).  Eels appear to be stimulated to migrate downstream at night during the new moon and especially during floods (Sinha and Jones 1975).  For a detailed review of eel reproduction and migration see Sinha and Jones (1975).  Mature females contain 3 million eggs per 1 kg body weight (Coad 2005). The average life span is 10 – 20 years.  The maximum reported age for a specimen kept in aquarium is 85 years (Svärdson 1949 in Deedler 1970; Froese and Pauly 2005).

Anguilla anguilla has been artificially hybridized with the Japanese eel A. japonica (Okamura et al. 2004).

Means of Introduction: Skinner (1971) suggested that some California anguillids may have arrived in ballast water of foreign ships. However, McCosker (1989) discounted ballast water as a vector. In general, eels caught in California waters 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).

Status: Reported from California but failed.

Impact of Introduction: Unknown.  Introduced anguillids may prey on trout and young salmon, and also may compete with salmonids and other native fishes for food (McCosker 1989, Coad 2005).  Additionally, eels can attack commercial fishes trapped in nets and therefore may constitute a potential loss to fisheries (Coad 2005).  Because eels do not reproduce in captivity, their culture requires removal of live eels from the wild.  Consequently, there is a high probability for introduction of new diseases, pathogens, and parasites (McCosker 1989).  European eels have been diagnosed with at least 29 diseases, including bacterial, parasitic and fungal infections (Froese and Pauly 2005).  A nematode parasite, Anguillicola crassus, was transferred to European eels from A. japonica and the native A. rostrata.

Remarks: There is still some uncertainty associated with the identification of the two California A. anguilla specimens.  Because each had 114 vertebrae, Williamson and Tabeta (1991) indicated that these fish cannot be reliably distinguished from A. japonica.

Anguillids are a popular food fish in many regions of the world. 

Eels can also travel overland during rainy periods, demonstrating that they are not easily contained (McCosker 1989).  Because of potential impacts, California has made the importation, sale, or culture of live anguillids illegal.  According to Williamson and Tabeta (1991), the Pacific Ocean near California does not seem to have an area suitable for Anguilla spawning, and, therefore, eels introduced into the western United States probably would not reproduce successfully.

The blood of the European eels is poisonous, but the poison is destroyed by cooking (Coad 2005).

Voucher specimens: California (CAS 27136, 39012).

References: (click for full references)

Berg, L. S.  1964.  Freshwater Fishes in the U.S.S.R. and Neighbouring Countries.  Vol. 2., Fourth edition.  Translated from Russian by Israel Program for Scientific Translations, Jerusalem, IPST Catalog No. 742.  496 pp.

Coad, B. W.  1995.  Freshwater fishes of Iran.  Acta Sci. Nat. Acad. Sci. Brno. 29:1-64.  Available online at:  http://www.briancoad.com/main.asp?page=titlepage.htm

Deedler, C. L.  1970.  Synopsis of biological data on the eel Anguilla anguilla (Linnaeus) 1758.  FAO Fisheries Synopsis No. 80.  FAO, Rome. 

Eschmeyer, W. N., C. J. Ferraris, Jr., M. D. Hoang and D. J. Long.  1998.  A Catalog of the Species of Fishes.  Preliminary Version 2, November 1996.  California Academy of Sciences.  Available online at:  http://www.calacademy.org/research/ichthyology/species/.

FAO.  1997. FAO Database on Introduced Aquatic Species.  FAO Database on Introduced Aquatic Species, FAO, Rome.

Froese, R. and D. Pauly. Editors. 2005. FishBase.  World Wide Web electronic publication.
www.fishbase.org.

Golani, D. and D. Mires.  2000.  Introduction of fishes to the freshwater system of Israel.  Bamidgeh 52: 47-60.

Hillman, J. C.  1993.  List of introduced species of Eritrea. Compiled by staff of the Research Section, Ministry of Marine Resources, Massawa, Eritrea. 1 p.

Krupp, F. and W. Schneider.  1989.  The fishes of the Jordan River drainage basin and Azraq Oasis. p. 347-416. In Fauna of Saudi Arabia. vol. 10.

Maitland, P. S.  1977.  Freshwater Fishes of Britain and Europe.  The Hamlyn Publishing Group Ltd., London, UK.  256 pp.  

McCosker, J. E.  1989.  Freshwater eels (Family Anguillidae) in California: current conditions and future scenarios.  Calif. Fish and Game. 75: 4-11.

Miyai, T., J. Aoyama, S. Sasai, J. G. Inoue, M. J. Miller and K. Tsukamoto.  2004.  Ecological aspects of the downstream migration of introduced European eels in the Uono River, Japan.  Environmental Biology of Fishes 71: 105-114.

Moriarty, C.  1986.  Riverine migration of young eels Anguilla anguilla (L.).  Vie et milieu 36: 266.

Okamura, A., H. Zhang, T. Utoh, A. Akazawa, Y. Yamada, N. Horie, N. Mikawa, S. Tanaka and H. P. Oka.  2004.  Artificial hybrid between Anguilla anguilla and A. japonica.  Journal of Fish Biology 64: 1450-1454. 

Reshetnikov, Y.S.  2003.  Atlas of Russian Freshwater Fishes.  Vols 1 & 2.  Moscow, Nauka.

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

Sinha, V. R. P. and J. W. Jones.  1975.  The European Freshwater Eel.  Liverpool University Press, United Kingdom.  146 pp.

Tosi, L., P. Tongiorgi, A. Spampanato, C. Sola and L. Sala.  1986.  Influence of temperature and salinity on the orientation of the glass eels of Anguilla anguilla during migration from the sea to fresh waters.  Nova Thalassia 8: 621-622.

Vollestad, L. A., B. Jonsson, N. A. Hvidsten, T. F. Naesje, O. Haraldstad and J. Ruud-Hansen.  1986.  Environmental factors regulating the seaward migration of European silver eels (Anguilla anguilla).  Canadian Journal of Fisheries and Aquatic Sciences 43: 1909-1916.

Welcomme, R. L.  1988.  International introductions of inland aquatic species.  FAO Fish. Tech. Pap. 294. 328 pp.

Wheeler, A. 1978. Key to the fishes of northern Europe. Frederick Warne Ltd., London, England.

Williamson, G. R., and O. Tabeta. 1991. Search for Anguilla eels on the West Coast of North America and on the Aleutian and Hawaiian Islands. Japanese Journal of Ichthyology 38(3):315-317.

Xie, Y., Z. Lin, W. P. Gregg and D. Li.  2001.  Invasive species in China - an overview.  Biodiversity and Conservation 10:1317-1341.

Other Resources:
US Fish and Wildlife Service Ecological Risk Screening Summary for Anguilla anguilla

Author: Schofield, P.J., and Fuller, P.

Peer Review Date: 3/5/2011

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.