Taxonomy & naming
Anguilla rostrata was described by the French naturalist Charles Alexandre Lesueur in 1817. The Catalog of Fishes (Eschmeyer, CAS) places it in the genus Anguilla Garsault, 1764 — the type genus of the family Anguillidae, order Anguilliformes. This lineage, the catadromous freshwater eels, represents true eels in the strict sense: they are Anguilliformes, and their closest relatives are the marine eels rather than the spiny eels (Mastacembelidae, order Synbranchiformes) or swamp eels (Synbranchidae), both of which are convergent in body form.
The specific epithet rostrata is Latin for 'beaked' or 'snout-bearing', referring to the pointed snout that distinguishes A. rostrata from the European eel A. anguilla, which has a slightly broader jaw. The American eel is the sole Anguilla species native to eastern North America. The genus includes roughly 18 recognised species distributed across the Northern Atlantic and Indo-Pacific, and the African Anguilla species (notably A. marmorata, A. bengalensis and A. mossambica) are morphologically cryptic and require DNA barcoding to distinguish reliably.
Morphology
The American eel is a large, serpentine fish reaching up to 60 in total length, though most individuals encountered in fresh water are considerably smaller; common length in the literature is around 19.5 in. Males are typically smaller than females and are more often found in brackish and estuarine habitats, while large females — which can grow to well over a metre — tend to move furthest inland into rivers and lakes.
The body is greatly elongate, with continuous dorsal, caudal and anal fins that taper to a rounded tip. The skin is slimy and scaleless to the naked eye; tiny cycloid scales are embedded in the dermis in a basket-weave pattern and become visible only in adults. Coloration changes markedly with life stage: leptocephalus larvae are transparent; glass eels entering fresh water are still largely transparent; elvers and juvenile 'yellow eels' are olive to yellowish-brown on the flanks; sexually maturing 'silver eels' destined for the spawning migration develop a silvery belly, enlarged eyes, and a darkened back as part of their oceanic transformation.
Habitat
During the continental growth phase, the American eel occupies an exceptionally broad range of freshwater and brackish habitats — rivers, streams, muddy or silt-bottomed lakes with continuous flow, estuaries, coastal lagoons and tidal creeks — from Greenland and Iceland south through eastern North America to Panama and the West Indies. Small eels tend to occupy faster, shallower reaches; larger, older fish favour slow, deep, muddy habitats where they can burrow into soft substrate by day and forage at night.
The species tolerates a wide temperature range, from near 32 °F in winter (under ice, where it becomes torpid) to about 77 °F in summer, with an overall preferred mean around 43 °F recorded in FishBase's compiled data. It is euryhaline — tolerant of both fresh and salt water — which underpins its ability to reach rivers far from the coast and to persist through the entire salinity gradient of an estuary. The spawning habitat is entirely different: the Sargasso Sea, roughly at 26°N, 55°W, at depths of 1312–2297 ft, where the larvae hatch and begin their drift.
Feeding
The American eel is a generalist nocturnal predator and scavenger. It forages primarily after dark, using its well-developed olfactory sense and sensitive lateral line to hunt in turbid and low-light conditions. The diet recorded in the literature is broad: aquatic insect larvae (mayflies, dragonflies, stoneflies, caddisflies), gastropod molluscs, oligochaete worms, crustaceans, and small fish are all taken. It is an opportunist that will scavenge carrion as well as take live prey, and in rivers it is considered an important ecological link between benthic invertebrate production and larger predators.
In the aquarium, American eels are rarely kept intentionally (see In the aquarium), but captive individuals readily accept meaty live and frozen foods — earthworms, pieces of fish, crustaceans — offered after dark. They are cautious, burrowing hunters rather than active chasers, and they feed most confidently in subdued light.
Mating
Anguilla rostrata is semelparous: each individual mates exactly once in its lifetime, after which it dies. Sexual maturity is not reached until the fish has spent many years — typically 10 to 20 — growing in fresh or brackish water, and the precise trigger for the transition to reproductive condition is not fully understood, though age, size, and environmental cues (including photoperiod and temperature) are all implicated.
Mature 'silver eels' undergo a dramatic pre-spawning transformation: the eyes enlarge, skin pigmentation changes to a silvery counter-shading suitable for the open ocean, the gut degenerates (they stop feeding entirely), and the gonads develop. They then leave their freshwater habitat in autumn, migrate downstream, and enter the ocean. The destination is the Sargasso Sea — a shared spawning ground used by both the American eel and the European eel (A. anguilla) in broadly overlapping but apparently distinct areas — where spawning takes place at depths of hundreds of metres. The details of courtship and spawning at sea remain almost completely unknown; no wild spawning event has been directly observed.
Breeding
The American eel cannot be bred in captivity. This is not a husbandry limitation that better technique might overcome; it reflects the eel's biology — its reproductive system does not fully mature without the oceanic spawning migration, and the gonads of fish held in fresh water remain largely undeveloped. Hormonal induction can force partial gametogenesis in research settings, but the full breeding cycle has never been completed under artificial conditions.
In nature, eggs are broadcast-spawned in the open ocean, hatch into leptocephalus larvae — thin, transparent, leaf-shaped — and drift in oceanic currents for approximately one year before metamorphosing into glass eels and riding coastal currents to North American shores. Glass eels enter estuaries and migrate upstream as elvers. The entire farming and ranching industry for Anguilla species worldwide depends on catching wild glass eels or elvers from this drift and raising them in tanks or ponds; there is no captive-bred eel stock. In the United States, glass-eel fishing is regulated and in some states restricted, and the commercial harvest of wild glass eels is a major trade that directly affects population recovery.
In the aquarium
The American eel is not a conventional aquarium fish, and keeping it is generally inadvisable for several practical and ethical reasons. Adult fish reach well over a metre in length and live for up to two decades, demanding an enormous, tightly secured aquarium. Like all true eels — and like the spiny and swamp eels too — Anguilla rostrata is an expert escape artist that can climb wet glass, squeeze through surprisingly small gaps, and survive out of water long enough to travel considerable distances. A fully sealed, eel-proof lid is essential for any eel species, and with A. rostrata this is non-negotiable.
The species is scaleless and unusually sensitive to copper-based medications, which are common treatments for aquarium disease; standard off-the-shelf remedies can be lethal. It is also nocturnal and cryptic, spending most daylight hours burrowed into soft substrate or wedged under cover. In much of its range, wild-caught American eels are subject to fisheries regulation or outright protection, making acquisition legally complex. For those who keep them, a large species-only or large-tankmate setup with a deep sand bed, extensive cover, and meaty evening feeds provides the best conditions. The fish is intelligent and long-lived, but it belongs in its rivers, not in a tank.
Conservation
The American eel is assessed as Endangered (EN) on the IUCN Red List (assessed 2014), and U.S. Atlantic stocks have declined to historic lows. The threats are numerous and mutually reinforcing: overfishing of glass eels and adults, physical fragmentation of river habitat by dams and weirs that block upstream migration and downstream spawning runs, water pollution and eutrophication, the parasitic swim-bladder nematode Anguillicola crassus (introduced from Asia), and the impacts of climate change on the Sargasso Sea spawning environment and larval drift patterns.
Dams are a particularly acute problem because the American eel is the only freshwater fish that migrates throughout the entire eastern North American watershed, from small headwater streams to tidal estuaries, and any barrier to migration cuts off portions of the range permanently. Glass-eel and elver trading — a highly lucrative market driven by demand from East Asian aquaculture that relies entirely on wild-caught juvenile eels — has been subject to tightening regulation in Canada, the U.S. and Europe, but illegal harvests remain substantial. Conservation measures include trap-and-truck passage programmes at dams, glass-eel harvest quotas, and ongoing population monitoring, but population recovery has been slow and the species's single-lifetime breeding strategy means that losses of spawning adults are irreversible on a human timescale.