Taxonomy & naming
Electrophorus electricus was described by Linnaeus in 1766, originally in the genus Gymnotus alongside the banded knifefishes — a placement that correctly recognised, from the very start, that the electric eel is a knifefish. It sits in the family Gymnotidae within the order Gymnotiformes, the New-World electric knifefishes, and its closest relatives are the banded knifefishes of the genus Gymnotus. The English name "eel" is purely descriptive of its long, cylindrical, finless body; it has nothing to do with the true eels (Anguilliformes), which are a separate lineage of bony fish covered in this atlas under Eels.
For two and a half centuries the electric eel was considered a single, wide-ranging species. In 2019 a study by de Santana and colleagues showed that it is in fact three: E. electricus in the stricter sense, confined to the uplands of the Guiana Shield in the north; E. voltai, of the Brazilian Shield to the south, which was recorded producing an 860-volt discharge, the strongest of any known animal; and E. varii, of the central Amazonian lowlands. This account covers E. electricus proper — the northern, Guiana-Shield species. The Catalog of Fishes is the authority for the valid names.
Morphology
The electric eel is a long, heavy, cylindrical fish that reaches around two metres and can weigh some twenty kilograms — by a wide margin the largest of all the knifefishes. Like the rest of the order it has no dorsal or tail fin and swims by rippling a long anal fin along the underside; the body is otherwise smooth, scaleless and grey-brown to olive, often with a paler, yellow-orange throat. The eyes are small and, in old animals, of little use, matching a fish that works by electricity and by feel.
Most of the body — around four-fifths of its length — is given over to the electric organs, not to guts, which are packed into a small space just behind the head. There are three organs: the large main organ and Sachs' organ produce the sensing and the high-voltage output, while Hunter's organ contributes to both. It is this enormous investment in electrogenic tissue, thousands of stacked electrocyte cells wired like batteries in series, that lets the fish generate the voltages it is famous for.
Habitat
Electrophorus electricus lives in the fresh waters of the Guiana Shield in northern South America — the highland rivers, streams, rapids and associated lowlands of the Guianas and neighbouring drainages. Its typical haunts are warm, still or slow, often muddy or shaded waters: floodplain pools, swamps, creeks and river margins, frequently poorly oxygenated.
Those low-oxygen conditions are why the electric eel became an air-breather. It is an obligate air-breather: the lining of its mouth is richly folded and vascularised, and the fish must rise to the surface every few minutes to gulp air, from which it draws most of its oxygen. Held underwater, it drowns. This ability lets it thrive where many fish cannot — in warm, stagnant, deoxygenated backwaters — and it shapes everything about how the animal would have to be housed: a covered but accessible surface, warm water, and a great deal of room.
Feeding
The electric eel is a predator, and its electricity is central to how it hunts. Alongside the weak discharges it uses, like other knifefish, to navigate and to sense its surroundings, it produces high-voltage volleys that stun prey. Research has shown the eel can use these discharges with startling precision — remotely triggering the muscles of a hidden fish to make it twitch and reveal itself, then delivering a volley that immobilises it before it is swallowed whole. Larger eels have even been observed launching from the water to press a discharge directly onto a threat.
Its diet is made up of fish, along with invertebrates and small vertebrates such as amphibians, taken across the warm lowland and shield waters it inhabits. Young eels start on invertebrates and take fish as they grow. In captivity — which in practice means a public aquarium — it is fed whole fish and other meaty foods; feeding a two-metre fish that can deliver a dangerous shock is, understandably, a job done with great care and proper equipment.
Mating
Breeding in the electric eel is tied to the dry season. As waters shrink and warm, a male constructs a nest — a mass of foam bound with saliva, hidden in cover — into which a female lays her eggs. Weak electric signalling is thought to play a part in bringing the pair together in the murky water where they live, as it does across the order, though the details of electric courtship in this species are less studied than in the small, laboratory-friendly ghost knifefishes.
What is unusual, and well documented, is what follows. Unlike most of its relatives, the electric eel is a devoted parent: the male stays with the nest and guards the eggs and the developing larvae. Thousands of young may hatch in a single nest under his protection.
Breeding
The electric eel is very rarely bred in captivity, and essentially never in private hands — the fish is far too large, and its needs far too specialised, for a home aquarium. Successful reproduction has been reported chiefly in the wild and, occasionally, in large public-aquarium settings, following the natural pattern: a dry-season foam nest built and guarded by the male, into which the female spawns, with the male tending the eggs and the shoal of larvae that hatch from them.
The young grow quickly and begin producing weak electric discharges early in life, well before they can generate a dangerous shock. For the hobby, the honest position is simple: this is not a fish to breed, or indeed to keep, outside a specialist institution, and almost every electric eel most people will ever see is a display animal in a public aquarium rather than a captive-bred pet.
In the aquarium
For all but a handful of specialist and public aquariums, the honest advice on the electric eel is: do not. It grows to around two metres, is a powerful obligate air-breather that needs a large, warm, filtered volume of water with constant access to the surface, and it produces a discharge that is genuinely dangerous to people — a shock capable of causing painful injury, falls and, in vulnerable individuals, worse. It is a fish that demands a purpose-built system, careful handling protocols and trained keepers.
Where it is kept properly, it is a compelling display animal: intelligent, responsive, and often surprisingly interactive with familiar keepers, some of whom report the eel learning feeding routines. Many public aquariums wire the tank to a speaker or light array so visitors can hear or see the discharges when the eel feeds. But none of that translates to the living room. Its scaleless skin still means care with medications and pristine, warm water, and its size and voltage put it firmly outside the home hobby. The right way to admire an electric eel is through the glass of a large institution — and the right thing to know about it is that it is a knifefish, not an eel at all.
Conservation
The electric eel is assessed as Least Concern on the IUCN Red List. It is widespread across suitable lowland and shield waters in northern South America, tolerant of the warm, deoxygenated habitats that exclude many fish, and not a significant target of the ornamental trade — its size and its shock see to that. Populations are considered stable.
The more interesting conservation story is scientific rather than one of threat. The 2019 discovery that the familiar electric eel is really three species — one of them, E. voltai, the strongest bioelectricity generator known — is a reminder of how much basic biology remains undescribed even in a fish this famous, and of how the geological history of the Amazon, which once flowed the other way, shaped the animals living in it. The priorities for the electric eels are the ones common to Amazonian fish generally: intact, unpolluted water, and continued study of a group whose diversity we have only just begun to appreciate.