Picture by Chad Thomas, Texas State University-San Marcos

Anguilla rostrata

American eel

Type Locality

Cayuga Lake, NY (Lesueur 1817).

Etymology/Derivation of Scientific Name

Anguilla, Latin for eel; rostrata, Latin for “beaked or curved”, presumably a characteristic of which only Lesueur was aware (Scharpf 2005).

Synonymy

Muraena rostrata Lesueur 1817:81.

Anguilla chrysypa Evermann 1899:308.

Anguilla rostrata Hay 1883:73; Cook 1959:144 (Ross 2001).

Characters

Maximum size: 1,200 mm, 47 in (Lee 1980). 

Coloration: Mature with a metallic sheen, back and sides blackish or bronze with purple reflections, and black pectoral fins at time of downstream migrations. Maturing females with copper colored sides, dark dorsal surface, and darkly mottled ventral surface or silvery-white. Migrating eels found in the ocean were silver, with the dorsal aspect of the pectoral and caudal fins darkly pigmented. Individuals may transition from bronze to silver as spawning migration progresses.  As individual matures, the eye develops coloration termed “retinal gold” (Hardy 1978).

Counts: Vertebrae 103-111; branchiostegals 9-13 (Hardy 1978).

Body shape:  Body snakelike, crossection is round anteriorly and laterally compressed posteriorly; snout depressed, broad, blunt (Hardy 1978).

Mouth position: Mouth large, slightly oblique; gape extended to posterior margin of eye (Hardy 1978).

Morphology: Teeth in bands on jaws and vomer (Hardy 1978). Scales small, cycloid and embedded, often difficult to see without magnification; lateral line well-developed and accentuated; dorsal, caudal, and anal fins continuous; dorsal origin far behind pectorals, nearer vent than gill openings (Hardy 1978).

Distribution (Native and Introduced)

U.S. distribution: Atlantic, Caribbean, and Gulf drainages of North America, Central America, and South America.

Texas distribution: Originally found in large rivers from the Red River to the Rio Grande. Extirpated in several drainages, attributed to reservoirs that impede upstream migration (Hubbs et al. 1991). Warren et al. (2000) listed the following drainage units for distribution of american eel in the state: Red River (from the mouth upstream to and including the Kiamichi River), Sabine Lake (including minor coastal drainages west to Galveston Bay), Galveston Bay (including minor coastal drainages west to mouth of Brazos River), Brazos River, Colorado River, San Antonio Bay (including minor coastal drainages west of mouth of Colorado River to mouth of Nueces River), Nueces River. Hubbs (2002) reported that dams have precluded young eels from repopulating Caddo Lake in northeast Texas.

[Additional literature noting collection of this species from Texas locations includes, but is not limited to the following: Riggs and Bonn (1959); Edwards and Contreras-Balderas (1991).]

Abundance/Conservation status (Federal, State, Non-governmental organizations):

Currently secure (Warren et al. 2000) although susceptible to extirpations. 

Habitat Associations

Macrohabitat: Found in a variety of aquatic environments (streams and reservoirs) in drainages connected to marine environments (Lee 1980). Adults occasionally found in landlocked lakes, primarily in the northeastern United States (Facey and Van Den Avyle 1987). Females encountered most frequently in freshwater (Helfman et al. 1984; Lee 1980).

Mesohabitat: Postlarval eels tend to be bottom-dwellers, hiding in burrows, tubes, snags, plant masses, other types of shelter, or the substrate itself (Fahay 1978; Van Den Avyle 1984). Large eels were associated with slow, deep, muddy habitats; small eels were associated with faster currents, in upper coastal plain streams of the central Savannah River drainage, South Carolina (Meffe and Sheldon 1988). In Maryland streams, higher densities of eels occurred at sites with greater velocity-depth diversity, at which four habitats were present: slow (<0.3 m/s)-deep (>0.5 m), slow-shallow (<0.5 m), fast (>0.3 m/s)-deep, and fast-shallow (Wiley et al. 2004). Specimens collected from mud bank habitat with hoop nets in the Missouri River (Robinson 1977). Nocturnal; uses cover during daylight hours (Van Den Avyle 1984; Baras et al. 1998). American eels prefer highly oxygenated water (Hill 1969).

Biology

Spawning season: February - April (Facey and Van Den Avyle 1987); possibly January - July (Hardy 1978), or August (Van Den Avyle 1984).

Spawning location: Adults breed in the mid-Atlantic Ocean (Lee 1980).

Reproductive strategy: Broadcast spawn eggs.  Eggs and leptocephalus larvae drift in the water column and are carried by ocean currents to continental drainages along western Atlantic Coast. (Hardy 1978; Wippelhauser et al. 1985).

Fecundity: 413,000-2,561,000 eggs (latter amount obtained from 724 mm long female, weighing 755 g, 1.66 lb) based on counts from females migrating from Chesapeake Bay (Wenner 1972; Wenner and Musick 1974). Ovarian eggs mostly spherical (smaller developing eggs cuboidal) with centrally located nucleus (Wenner 1972). According to Facey and Van Den Avyle (1987), fecundity is between about 500,000-4,000,000 eggs, with large individuals capable of producing up to 8,500,000 eggs.

Age/size at maturation: Sexual maturity not reached until at least 5 years, and often 20+ years for females (Hardy 1978; Haro et al. 2000); mature slowly, in 7 to 30+ years (K. Oliveira, Univ. of Maine, pers. comm. in: ASMFC 2000). Males reported to mature at about 280 mm (11 in), and females at about 457 mm (18 in); however females may mature at lesser sizes (Hardy 1978).

Migration: Catadromous (Simon 1999); adults breed at sea after living most of their lives in fresh and brackish waters (Lee 1980). Generally, “glass eels” (larvae) move inshore into brackish or freshwater and transform (gradually developing pigmentation) into “elvers” in late winter or early spring (Fahay 1978; Helfman et al. 1984). Elvers remain in fresh water for several years, and are called “yellow eels”. Yellow eels may be sexually differentiated or undifferentiated, or hermaphroditic, but none are capable of reproduction and are therefore immature. Maturing eels undergo changes in body color and morphology, and migrate downriver and through the ocean to spawning grounds; these individuals are known as “bronze eels” or “silver eels” (Van Den Avyle 1984).

Longevity:  Landlocked eels librated as elvers in Sherman Lake, Michigan lived to 35 – 40 years (Van Den Avyle 1984); yellow eels from northern rivers reported to live 15-20 years (Fahay 1978). Adult eels apparently die after spawning, as none have been observed to migrate up rivers, and spent eels have not been reported (Hardy 1978; Facey and Van Den Avyle 1987).

Food habits:  Invertivore/carnivore; voracious piscivore; main food items are fishes and invertebrates (Goldstein and Simon 1999). Three basic feeding modes include: 1) inertial suction of food – drawing small items into mouth and esophagus; 2) grasp and shake – grasping of larger items in mouth and shaking of head and body, thereby tearing small pieces from larger item; 3) rotational or spin feeding – grasping of larger items in mouth and spinning on long axis, thereby tearing larger prey items into smaller pieces (Helfman and Clark 1986). In the James River, Virginia, eels feed on aquatic insects in freshwater, shifting to larger insects, crustaceans, fishes, and other vertebrates (i.e. frogs) as eel size increases (Ranidae; Lookabaugh and Angermeier 1992). Polychaetes, crustaceans, and bivalves were the most important food items of eels in the brackish water regions of three Virginia rivers (Lower Chesapeake Bay; Wenner and Musick 1975). Analysis of stomach contents from individuals found in New Jersey streams indicated a gradual increase in size of food organisms taken with increase in size of eels; specimens <400 mm (15.7 in) primarily consumed insects while specimens >400 mm (15.7 in) more frequently consumed fish and crustaceans (Ogden 1970). In Canada, 90% of the diet consisted of larval aquatic insects (Smith and Saunders 1955).

Growth/Population structure: Growth rates within year classes highly variable, leading to considerable variation in length at age and poor predictability of age from size (Van Den Avyle 1984). Females grow faster than males (Helfman et al. 1984; Van Den Avyle 1984; Oliveira 1999). In maritime provinces of Canada, elvers may reach lengths of at least 80-100 mm (3-4 in)  during their first year in fresh water (Smith and Saunders 1955). Male silver eels migrating from Chesapeake Bay averaged 372 mm (14.6 in); female silver eels averaged 633 mm, 24.9 in (Wenner and Musick 1974). Specimens from the Altamaha River, Georgia, were smaller, younger, and matured more rapidly than those at more northern latitudes; glass eels captured in late winter were 49-56 mm (1.9-2.2 in) long and 250-300 days old; maturing silver eels captured during late winter/early spring were 353-587 mm (13.9-23.1 in) long and 3-6 years old (Helfman et al. 1984).

Phylogeny and morphologically similar fishes:

Morphologically similar but genetically distinct from the European eel, A. anguilla (Lee 1980); A. rostrata comprised of one, genetically homogenous population (Avise et al. 1986). Both A. anguilla and A. rostrata exist in Icelandic habitats, and are known to hybridize within this range (Avise et al. 1990).

Host Records: 

The non-indigenous eel swimbladder nematode, Anguillicola crassus, has been documented to have significant negative impacts on eels in Texas and South Carolina (ASMFC 2000). Hoffman (1967) listed parasite species infecting eels including Protozoa, Trematoda, Cestoda, Nematoda, Acanthocephalan, Crustacea.

Commercial or Environmental Importance:

      Haro et al. (2000) presented evidence for a decline in the population of American eels from several widely distributed regions of North America from 1984–1995, and suggested numerous potential factors which may be influencing the decline: barriers to migration, habitat loss and alteration, hydro turbine mortality, oceanic conditions, over-fishing, parasitism, and pollution. The Atlantic States Marine Fisheries Commission developed a fisheries management plan designed to protect and restore the species (ASMFC 2000).

References

ASMFC (Atlantic States Marine Fisheries Commission). 2000. Interstate fishery management plan for American eel. ASMFC Fishery Management Report No. 36, Washington, D.C. 79 pp.

Avise, J.C., G.S. Helfman, N.C. Saunders, and L.S. Hales. 1986. Mitochondrial DNA differentiation in North Atlantic eel: population genetic consequences of an unusual life history pattern. Proc. Nat. Acad. Sci. 83:4350-4354.

Avise, J.C., W.S. Nelson, J. Arnold, R.K. Koehn, G.C. Williams, and V. Thorsteinsson. 1990. The evolutionary genetic status of Icelandic eels. Evolution 44(5):1254-1262.

Cook. F.A. 1959. Freshwater fishes in Mississippi. Mississippi Fish and Game Commission, Jackson. 239 pp.

Edwards, R.J., and S. Contreras-Balderas. 1991. Historical changes in the ichthyofauna of the lower Rio Grande (Rio Bravo del Norte), Texas and Mexico. The Southwestern Naturalist 36(2):201-212.

Evermann, B.W. 1899. Report on investigations by the U.S. Fish Commission in Mississippi, Louisiana, and Texas, in 1897. Rept. U.S. Fish Comm. 24:287-310.

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 Wild. Serv. Biol. Rep. 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.

Goldstein, R.M., and T.P. Simon. 1999. Toward a united definition of guild structure for feeding ecology of North American freshwater fishes. pp. 123-202 in T.P. Simon, editor. Assessing the sustainability and biological integrity of water resources using fish communities. CRC Press, Boca Raton, Florida. 671 pp.

Hardy, J.D., Jr. 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.

Hay, O.P. 1883. On a collection of fishes from lower Mississippi valley. Proc. Bull. U.S. Fish Comm. 2:57-75.

Helfman, G.S., E.L. Bozeman, and E.B. Brothers. 1984. Size, age, and sex of American eels in a Georgia River.  Transactions of the American Fisheries Society 113:132-141.

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. 486 pp.

Hubbs, C. 2002. A preliminary checklist of the fishes of Caddo Lake in northeast Texas. Texas Journal of Science 54(2):111-124.

Hubbs, C., R.J. Edwards, and G.P. Garrett. 1991. An annotated checklist of the freshwater fishes of Texas, with keys to the identification of species. The Texas Journal of Science, Supplement  43(4):1-56.

Jessop, B.M. 1987. Migrating eels in Nova Scotia. Trans. Amer. Fish. Soc. 116:161-170.

Lee, D.S. 1980. Anguilla rostrata (Lesueur), American eel.  pp. 59 in D. S. Lee, et al.  Atlas of North American Freshwater Fishes.  N.C. State Mus. Nat. Hist., Raleigh, i-r+854 pp.

Lesueur, C.A. 1817.  A short description of five (supposed) new species of the genus Muraena, discovered by Mr. Lesueur, in the year 1816.  J. Acad. Nat. Sci. Phil. 1(1):81-83.

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

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.

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.

Oliveira, K. 1999. Life history characteristics and strategies of the American eel, Anguilla rostrata. Canadian Journal of Fisheries and Aquatic Sciences 56:795-802.

Riggs, C.D., and E.W. Bonn. 1959. An annotated list of the fishes of Lake Texoma, Oklahoma and Texas. The Southwestern Naturalist 4(4):157-168.

Robinson, J.W. 1977. The utilization of dikes by certain fishes in the Missouri River. Federal Aid Project No. 2-199-R. Missouri Department of Conservation, Jefferson City. 14 pp.

Scharpf, C. 2005. Annotated checklist of North American freshwater fishes, including subspecies and undescribed forms. Part 1: Petromyzontidae through Cyprinidae. American Currents, Special Publicaiton 31(4):1-44.

Simon, T.P. 1999. Assessment of Balon’s reproductive guilds with application to Midwestern North American Freshwater Fishes, pp. 97-121. In: Simon, T.L. (ed.). Assessing the sustainability and biological integrity of water resources using fish communities. CRC Press. Boca Raton, Florida. 671 pp.

Smith, M.W., and J.W. Saunders. 1955. The American eel in certain fresh waters of the maritime provinces of Canada.  Journal of the Fisheries Research Board of Canada 12:238-269.

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 Wildl. Serv. FWS/OBS-82/11.24. U.S. Army Corps of Engineers, TR EL-82-4. 20 pp.

Wippelhauser, G.S., J.D. McCleave, and R.C. Kleckner. 1985. Anguilla rostrata leptocephali in the Sargasso Sea during February and March 1981. Dana 4:93-98.

Warren, M.L., Jr., B.M. Burr, S.J. Walsh, H.L. Bart, Jr., R.C. Cashner, D.A. Etnier, B.J. Freeman, B.R. Kuhajda, R.L. Mayden, H.W. Robison, S.T. Ross, and W.C. Starnes. 2000. Diversity, Distribution, and Conservation status of the native freshwater fishes of the southern United States. Fisheries 25(10):7-29.

Wenner, C.A., and J.A. Musick. 1974. Fecundity and gonad observations of the American eel, Anguilla rostrata, migrating from Chesapeake Bay, Virginia. J. Fish. Res. Board Can. 31:1387-1391.

Wenner, C.A., and J.A. Musick. 1975. Food habits and seasonal abundance of the American eel, Anguilla rostrata, from the lower Chesapeake Bay. Chesapeake Science 16(1):62-66.

Wiley, D.J., R.P. Morgan, II, R.H. Hilderbrand, R.L. Raesly, and D.L. Shumway. 2004. Relations between physical habitat and American eel abundance in five river basins in Maryland. Trans. Amer. Fish. Soc. 133:515-526.