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The American eel, Anguilla rostrata, is a facultative catadromous fish found on the eastern coast of North America. Eels (Anguilla spp.) are fish belonging to the elopomorph superorder, a group of phylogenetically ancient teleosts. The American eel has a slender snakelike body that is covered with a mucous layer, which makes the eel appear to be naked and slimy despite the presence of minute scales. A long dorsal fin runs from the middle of the back and is continuous with a similar ventral fin. Pelvic fins are absent, and relatively small pectoral fin can be found near the midline, followed the head and gill-covers. Variations exist in coloration, from olive green, brown shading to greenish-yellow and light gray or white on the belly. Eels from clear water are often lighter than those from dark, tannic acid streams 
The eel lives in fresh water and estuaries and only leaves these habitats to enter the Atlantic ocean to start its spawning migration to the Sargasso Sea. Spawning takes place far offshore where the eggs hatch. The female can lay up to 4 million buoyant eggs a year, but dies after egg-laying. After the eggs hatch and the early-stage larvae develop into leptocephali, the young eels move toward North America where they metamorphose into glass eels and enter freshwater systems where they grow as yellow eels until they begin to mature.
The American eel is found along the Atlantic coast including Chesapeake Bay and the Hudson River and as far north as the St. Lawrence River region. Is also present in the river systems of the eastern Gulf of Mexico and in some areas further south. Like all anguillid eels, American eels hunt at night, and during the day it hides in mud, sand or gravel very close to shore, roughly 5 to 6 feet under. They feed on crustaceans, aquatic insects, small insects, and probably any aquatic organisms that they can find and eat.
American eels are economically important in various areas along the East Coast as bait for fishing for sport fishes such as the striped bass, or as a food fish in some areas. Their recruitment stage, the glass eel, are also caught and sold for use in aquaculture in a few areas, although this is now restricted in most areas.
Eels were once an abundant species in rivers, and were an important fishery for aboriginal people. The construction of hydroelectric dams, however, has blocked their migrations and locally exterminated eels in many watersheds. For example, in Canada, the vast numbers of eels in the St. Lawrence and Ottawa Rivers have dwindled.
The American Eel Anguilla rostrata was first described in 1817 by Lesueur. Anguilla is Latin for eel, and rostrata is a Latin word that can mean either "breaked or curved" or "long nose". French: Anguille d’Amérique, Spanish: Anguila americana.
The American eel body is elongate and snake-like. Its dorsal and anal fins are confluent with the rudimentary caudal fin. It lacks ventral fins but pectoral fins are present. The lateral line is well-developed and complete. The head is long and conical, with rather small, well-developed eyes. The mouth is terminal with jaws that are not particularly elongated. The teeth are small, pectinate or setiform in several series on the jaws and the vomer. Minute teeth also present on the pharyngeal bones, forming a patch on the upper pharyngeals. Tongue present with thick lips that are attached by a frenum in front. Nostril are superior and well separated. Gill openings are partly below pectoral fins, relatively well-developed and well separated from one another. Inner gill slits are wide.
The scales are small, rudimentary, cycloid, relatively well embedded below the epidermis and therefore often difficult to see without magnification. The scales are not arranged in overlapping rows as they often are in other fish species but are rather irregular, in some places distributed like “parquet flooring”. In general, one row of scales lies at right angle to the next, although the rows immediately above and below the lateral line lie at an angle of approximately 45°. Unlike other bony fishes, the first scales do not develop immediately after the larval stage but appear much later on.
Several morphological features distinguish the American eel from other eel species. Tesch (1977)  described three morphological characteristics which persist through all stages from larvae to maturing eels: the total number of vertebrae (mean 107.2), the number of myomeres (mean 108.2), and the distance between the origin of the dorsal fin to the anus (mean 9.1% of total length).
American eels can grow to 1.22m in length and to 7.5 kg in weight. Females are generally larger than males, lighter in color, with smaller eyes and higher fins.
The distribution of the American eel encompasses all accessible freshwater (streams and lakes), estuaries and coastal marine waters across a latitudinal range of 5 to 62 N. Their natural range includes the eastern North Atlantic Ocean coastline from Venezuela to Greenland and including Iceland ). Inland, this species extends into the Great Lakes and the Mississippi River.
Nonindigenous occurrences of this species in the United States were recorded from Lake Mead on the Colorado River and on the Arizona border (Minckley 1973). It was stocked on a few occasions in Sacramento and San Francisco bay, CA in the late 1800s. No apparent evidence of survival on these occasions was noted (Smith 1896; Shebley 1917; Shapovalov et al. 1981; McCosker 1989). It was also stocked and unintentionally introduced in various states, including Illinois (Milner 1874b; Goode 1884), Indiana (Gerking 1945), Nebraska, Nevada (Minckley 1973), North Carolina (Shute and Etnier 2000), Ohio and Pennsylvania (Scott and Crossman 1973; Busch et al. 1977; Trautman 1980), Wisconsin (Milner 1874b; Goode 1884). Stocking of this species also occurred in Utah in the late 1800s, but soon disappeared (Popov and Low 1953; Sigler and Miller 1963).
Eels are bottom dwellers. They hide in burrows, tubes, snags, masses of plants, other types of shelters. They are found in a variety of habitats including streams, rivers, and muddy or silt-bottomed lakes during their freshwater stage, as well as oceanic waters, coastal bays and estuaries. Individuals during the continental stage occasionally migrate between fresh, salt and brackish water habitats and have varying degrees of residence time in each. During winter, eels burrow under the mud and enter a state of torpor (or complete inactivity) at temperatures below 5°C. although they may occasionally be active during this period. Temperature requirements are suggested to be flexible. It has been found that American eels during elver stage can survive temperature as low as -0.8oC (Jefferies 1960). Barila and Stauffer (1980)  reported a final mean temperature preference at 16.7oC. Karlsson et al. (1984) disagreed with this interpretation and found the final temperature preference of 17.4 ± 2.0oC with a 95% confidence interval.
Seasonal patterns described by Fletcher and Anderson (1972) generalize annual movements from freshwater to estuaries and coastal bays to feed during spring, then either a return during the fall to overwinter (juvenile and immature adults), or a southward migration to the spawning grounds (silver eels Continental phase eels appear highly plastic in habitat use. Eels are extremely mobile and may access habitats that appear unavailable to them, using small watercourses or moving through wet grasses (Scott and Scott 1988). Small eels (<100 mm total length) are able to climb and may succeed in passing over vertical barriers. Habitat availability may be reduced by factors such as habitat deterioration, barriers to upstream migration (larger eels), and barriers (i.e. turbines) to downstream migration that can result in mortality.
The American eel’s complex life history begins far offshore in the Sargasso Sea in a semelparous and panmictic reproduction. From there, young eels drift with ocean currents and then migrate inland into streams, rivers and lakes. This journey may take many years to complete with some eels travelling as far as 6,000 kilometers. After reaching these freshwater bodies they feed and mature for approximately 10 to 25 years before migrating back to the Sargasso Sea in order to complete their life cycle.
Life stages are detailed below.
1. Eggs: The eggs hatch within a week of deposition in the Sargasso Sea. McCleave et al. (1987) suggested that hatching peaks in February and may continue until April. Wang and Tzeng (2000) proposed, on the basis of otolith back-calculations, that hatching occurs from March to October and peaks in August. However, Cieri and McCleave (2000) argued that these back-calculated spawning dates do not match collection evidence and may be explained by resorption. Fecundity for many eels is between about 0.5 to 4.0 million eggs, with larger individuals releasing as many as 8.5 million eggs (Wenner and Musick 1974). The diameter of egg is about 1.1mm. Fertilization is external, and adult eels are presumed to die after spawning. None has been reported to migrate up rivers.
2. Leptocephali: The leptocephalus is the larval form, a stage strikingly different from the adult form the eels will grow into. Leptocephali are transparent with a small pointed head and large teeth and are frequently described “leaf-like”. The laterally compressed larvae are passively transported west and north to the coastal waters on the eastern coast of North America, by the surface currents of the Gulf Stream system, a journey that will last between 7 and 12 months (Schmidt 1922; Tesch 1977; Kleckner and McCleave 1982). Vertical distribution is usually restricted to the upper 350 m of the ocean (Kleckner and McCleave 1982; Castonguay and McCleave 1987). Growth has been evaluated at about 0.21 to 0.38 mm per day (Kleckner and McCleave 1985; Castonguay 1987; Tesch 1998; Wang and Tzeng 2000).
3. Glass eel: As they enter the continental shelf, leptocephali metamorphose into glass eels (juveniles), which are transparent and possess the typical elongate and serpentine eel shape (McCleave et al. 1987). The term glass eel refers to all developmental stages between the end of metamorphosis and full pigmentation (Tesch 2003). Metamorphosis occurs when leptocephali are about 55 to 65 mm long (Kleckner and McCleave 1985). Mean age at this metamorphosis has been evaluated at 200 days and estuarine arrival at 255 days; giving 55 days between glass eel metamorphosis and estuarine arrival (Wang and Tzeng 2000). Young eels use selective tidal stream transport to move up estuaries (Kleckner and McCleave 1982). As they enter coastal waters, the animals essentially transform from a pelagic oceanic organism to a benthic continental organism.
4. Elvers: Glass eels become progressively pigmented as they approach the shore; these eels are termed elvers. The melanic pigmentation process (Bertin 1951; Élie et al. 1982; Grellier et al. 1991) occurs when the young eels are in coastal waters. At this phase of the life cycle, the eel is still sexually undifferentiated. The elver stage lasts about three to twelve months. Elvers that enter fresh water may spend much of this period migrating upstream (Haro and Krueger 1991; Jessop 1998a). Elver influx is linked to increased temperature and reduced flow early in the migration season, and to tidal cycle influence later on (Tesch 1977; Kleckner and McCleave 1982; Martin 1995; Jessop 2003b).
5. Yellow eels: This is the sexually immature adult stage of American eel. They begin to develop a yellow color and a creamy or yellowish belly. In this phase, the eels are still mainly nocturnal. Those remained in estuarine environment continue to go through their life cycle more quickly than those traveled into freshwater. Those in freshwater, however, tend to live longer and attain much larger sizes. Sexual differentiation occurs during the yellow stage and appears to be strongly influenced by environmental conditions (Krueger and Oliveira 1997; Oliveira 1997; Krueger and Oliveira 1999). Krueger and Oliveira (1999) suggested that density was the primary environmental factor influencing the sex ratio of eels in a river, with high densities promoting the production of males. From life history traits of four rivers of Maine, Oliveira and McCleave (2000) evaluated that sexual differentiation was completed by 270 mm total length.
6. Silver eels: As the maturation process proceeds, the yellow eel metamorphoses into a silver eel. The silvering metamorphosis results in morphological and physiological modifications that prepare the animal to migrate back to the Sargasso Sea. The eel acquires a greyish colour with a whitish or cream coloration ventrally (Gray and Andrews 1971; Scott and Crossman 1973; Tesch 1977). The digestive tract degenerates (Pankhurst and Sorensen 1984; Durif 2003), the pectoral fins enlarge to improve swimming capacity (Pankhurst 1982a; McGrath et al. 2003; Durif 2003), eye diameter expands and visual pigments in the retina adapt to the oceanic environment (Vladykov 1966; Pankhurst 1982b; McGrath et al. 2003), the integument thickens (Tesch 1977; Pankhurst and Lythgoe 1982), percentage of somatic lipids increases to supply energy for migrating and spawning (Larsson et al. 1990; Tremblay 2004), gonadosomatic index (Verreault 2002; McGrath et al. 2003; Tremblay 2004) and oocyte diameter increase (Couillard et al. 1997), gonadotropin hormone (GTH-II) production increases (Durif et al. 2005), and osmoregulatory physiology changes (Dutil et al. 1987).
Eels are nocturnal and most of their feeding therefore occurs at night (Helfman 1986). Having a keen sense of smell, eels most likely depend on scent to find food. The American eel is a generalist species which colonizes a wide range of habitats. Their diet is therefore extremely diverse and includes most of the aquatic animals sharing the same environment.
Little is known about the food habits of leptocephali. Recent studies on other eel species (Otake et al. 1993; Mochioka and Iwamizu 1996) suggest that leptocephali do not feed on zooplankton but rather consume detrital particles such as marine snow and fecal pellets or particles such as discarded houses of larvacean tunicates.
Based on laboratory experiments on European glass eels, Lecomte-Finiger (1983) reported that they were morphologically and physiologically unable to feed. However, Tesch (1977) found that elvers at a later stage of pigmentation, stage VIA4 (Élie et al. 1982), were feeding. Stomach examination of elvers caught during their upstream migration in the Petite Trinité River on the north shore of the Gulf of St. Lawrence revealed that elvers fed primarily on insect larvae (Dutil et al. 1989).
The yellow eel is essentially a nocturnal benthic omnivore. Prey includes fishes, molluscs, bivalves, crustaceans, insect larvae, surface-dwelling insects, worms, frogs and plants. The eel prefers small prey animals which can easily be attacked. Food type varies with body size (Ogden 1970, cited in Tesch 1977). Stomachs of eels less than 40 cm and captured in streams contained mainly aquatic insect larvae, whereas larger eels fed predominantly on fishes and crayfishes. Insect abundance decreased in larger eels (Facey and LaBar 1981). The eel diet adapts to seasonal changes and the immediate environment. Feeding activity decreases or stops during the winter, and food intake ceases as eels physiologically prepare for the spawning migration.
Little information about predation on eels has been published. It was reported that elvers and small yellow eels are prey of largemouth bass and striped bass, although they were not a major parts of these predators' diet. Leptocephali, glass eels, elvers, and small yellow eels are likely to be eaten by various predatory fishes. Older eels are also known to eat incoming glass eels. They also fall prey to other species of eels, bald eagles, gulls, as well as other fish-eating birds 
The major outlet for U.S landings of yellow and silver eels is the EU market 
In the 1970s, the annual North Atlantic harvest averaged 125,418 kg, with an average value of $84,000. In 1977, the eel landings from Maine, New Hampshire, and Massachusetts were about 79,700, 2,700, and 143,300 kg, valued at $263,000, $5,000, and $170,000, respectively (US Department of Commerce 1984)
During the 1980s and early 1990s, the American eel was one of the top three species in commercial value to Ontario's fishing industry. At its peak, the eel harvest was valued at $600,000 and, in some years, eel accounted for almost half of the value of the entire commercial fish harvest from Lake Ontario. the commercial catch of eel has declined from approximately 223,000 kilograms (kg) in the early 1980s to 11,000 kg in 2002.
Substantial decline in numbers and fishery landings of American eels over their range in eastern Canada and the US was noted, raising concerns over the status of this . The number of juvenile eels in the Lake Ontario area decreased from 935,000 in 1985 to about 8000 in 1993 and was approaching zero levels in 2001. Rapid declines were also recorded in Virginia, as well as in New Brunswick and Prince Edward Island in Canada.
Because of its complex life cycle, the species face a broad range of threats, some of which are specific to certain growth stage. Being catadromous, the eels's reproductivity success depends heavily on free downstream passage for spawning migration. It also depends on the availability of diverse habitats for growth and maturation.
Sex ratio in the population can also be affected because males and females tend to utilize different habitats. Impacts on certain regions may greatly impact the number of either sex.
Despite being able to live in a wide range of temperatures and different levels of salinity, American eels are very sensitive to low dissolved oxygen level, which is typically found below dams. Contaminations of heavy metals, dioxins, chlordane, and polychlorinated biphenyls as well as pollutants from nonpoint source can bioaccumulate within the fat tissues of the eels, causing dangerous toxicity and reduced productivity. This problem is exacerbated due to the high fat content of eels.
Construction of dams and other irrigation facilities seriously decreases habitat availability and diversity for the eels. Dredging can affect migration, population distribution and prey availability. Overfishing or excessive harvesting of juveniles can also negatively impact local populations.
Other natural threats come from interspecific competition with exotic species like the flathead catfish (Pylodictis olivaris) and blue catfish (Ictalurus furcatus), pathogens and parasites, and changes in oceanographic conditions that can alter currents-this potentially alter larval transport and migration of juveniles back to freshwater streams.
Management of the species had been virtually non-existent till very recently. Information on the species is still limited and much more efforts are needed for a longterm plan to monitor localized populations.
- The Canadian province of Ontario has cancelled the commercial fishing quota since 2004. Eel sport fishery has been closed. Efforts have been made to improve the passage in which eels migrate across the hydroelectric dams on St. Lawrence River 
Some recommendations from the Department of Natural Resources of South Carolina:
In 2010, Greenpeace International has added the American eel to its seafood red list. "The Greenpeace International seafood red list is a list of fish that are commonly sold in supermarkets around the world, and which have a very high risk of being sourced from unsustainable fisheries."
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