Electric Eel (Electrophorus electricus): Facts and Shocks

Is the electric eel really an eel?

No. True eels belong to the order Anguilliformes, which includes the European eel, congers and morays. Electric eels belong to the Gymnotiformes, the South American knifefishes, a group of more than 200 species whose closest relatives are the catfishes. Together with carp and characins such as piranhas and tetras, they belong to a large group of fishes that share the Weberian apparatus, a chain of tiny bones linking the swim bladder to the inner ear and giving them sharp hearing. The long body is a case of convergent evolution, explained in is an electric eel an eel?

For more than 200 years, scientists recognized only one electric eel, first described by Carl Linnaeus in 1766. In 2019 a team led by C. David de Santana split the genus Electrophorus into three species, using DNA, skull shape, habitat and voltage:

• Electrophorus electricus, the original species, now known only from rivers of the Guiana Shield in the north.
• Electrophorus voltai, Volta’s electric eel, mainly from the Brazilian Shield to the south, named after the battery pioneer Alessandro Volta.
• Electrophorus varii, Vari’s electric eel, mainly in the lowland Amazon basin.

The three look almost identical from the outside, so most facts in older books apply to the genus as a whole.

What does an electric eel look like?

The electric eel has a long, thick body that is rounded at the front and flatter toward the tail, a broad, flattened head and a wide mouth that opens slightly upward. The smooth skin has no scales and is dark gray, brown or almost black above, often with a yellow, orange or reddish throat and belly. The eyes are small and its vision is poor.

There is no dorsal fin, no pelvic fins and no separate tail fin. Instead, one long anal fin with more than 400 fin rays runs along most of the underside. The eel swims by sending waves along this ribbon-like fin while keeping its body fairly straight, so it can glide forward or backward with equal ease. Rows of small pits on the head mark the lateral line, a sense organ that detects movement in the water.

Almost the whole fish is built for electricity. The heart, liver, stomach and other vital organs are packed into roughly the front fifth of the body, and the electric organs fill the remaining 80 percent. An electric eel can have up to about 300 vertebrae, and it keeps adding vertebrae as it grows.

How big do electric eels get?

Electric eels are among the largest freshwater fishes of South America. E. electricus can reach about 2 m (6.6 ft) and 20 kg (44 lb), and Volta’s electric eel is the largest of the three species and of all knifefishes, at up to about 2.5 m (8.2 ft) and 22 kg (49 lb). Most adults seen in the wild are smaller, roughly 0.7–2 m (2.3–6.6 ft) long.

Males grow bigger than females, by about 35 cm (14 in) in Volta’s electric eel. Males start breeding at about 1.2 m (3.9 ft) long, while females can breed from about 70 cm (2.3 ft). Young eels already produce weak electric pulses when they are only about 7 cm (2.8 in) long.

Habitat and range

Electric eels live only in fresh water in northern South America, in the Amazon and Orinoco basins and the rivers of the Guianas. Since the 2019 split, E. electricus in the strict sense is known from the Guiana Shield, an ancient upland region that covers Guyana, Suriname, French Guiana, southern Venezuela and the far north of Brazil. Volta’s electric eel lives mainly in rivers draining the Brazilian Shield south of the Amazon, and Vari’s electric eel in the lowland floodplains between the two shields.

Within these regions, electric eels prefer slow, muddy or shaded water: river bottoms, quiet backwaters, creeks, swamps and the pools left behind when rivers fall in the dry season. Many of these places are warm and low in oxygen, which few fish can tolerate. The electric eel copes by breathing air.

How does an electric eel breathe?

The electric eel is an obligate air breather, which means it must come to the surface to breathe or it will drown. Roughly every two minutes it rises, gulps air and holds it in its mouth, where the lining is folded and packed with blood vessels that absorb oxygen. Up to about 80 percent of its oxygen comes from air, its small gills do little, and much of its carbon dioxide leaves through the skin.

This lets electric eels survive in stagnant pools where most fish would suffocate. With wet skin, an electric eel can even survive out of water for some hours.

How electric eels use electricity

The electric organs are built from thousands of electrocytes, flat cells that evolved from muscle cells. Each produces only about 0.15 volts, but the cells are stacked in long rows, like the cells of a battery, so their voltages add up. An electric eel has three pairs of electric organs: the large main organ, Hunter’s organ and Sachs’ organ. The details are in how do electric eels make electricity?

The eel uses two main kinds of discharge. Weak pulses of about 10 volts, made mainly by Sachs’ organ, create an electric field around its body. Fish, rocks and plants distort the field, and electroreceptors in the skin detect the changes, so the eel can sense its surroundings in muddy water at night. This is called electrolocation.

Strong pulses come from the main organ, helped by Hunter’s organ. In the 2019 study, the strongest discharges measured were about 480 volts in E. electricus, 572 volts in Vari’s electric eel and 860 volts in Volta’s electric eel, the highest voltage known from any animal. Each pulse lasts only about 2 milliseconds, and the eel fires them in volleys of up to several hundred per second. For what this means for people, see how strong is an electric eel shock?

What do electric eels eat?

Adult electric eels are nocturnal predators that eat mainly fish, such as armored catfish and cichlids. Young eels feed on insects, small crustaceans and other invertebrates before moving on to fish.

Experiments by biologist Kenneth Catania showed how precise the hunt is. When an eel senses hidden prey, it can give two or three quick high-voltage pulses that make the prey’s muscles twitch, revealing its position. A full volley then makes the prey’s muscles lock, freezing it long enough for the eel to suck it into its mouth. With large or struggling prey, the eel can curl its body so its head and tail sit on either side of the victim, concentrating the shock.

Electric eels were long thought to hunt alone. In 2021, researchers described Volta’s electric eels in the Iriri River region of the Brazilian Amazon hunting as a team: dozens of eels herded small fish into a tight ball near the surface, and several eels then struck together with high-voltage discharges.

Reproduction and life cycle

Electric eels breed in the dry season, when falling water leaves pairs in small pools and swamps. The male builds a nest from his saliva, and the female lays her eggs in it. Field nests have held about 1,200 young on average, and a female may produce up to about 17,000 eggs over a season, laying them in batches. The first larvae to hatch eat eggs laid later.

The male guards the nest and young aggressively. In the lowland species, parental care can last about four months, while the two upland species, which live in faster rivers, seem to care for their young less.

Lifespan, predators and conservation status

How long electric eels live in the wild is unknown. In captivity, males have lived about 10–15 years and females about 12–22 years. Like many fish, electric eels keep growing throughout life.

Adults have few known predators, because their shocks deter most animals. Their eggs and young are more vulnerable, which is one reason the males guard them so closely.

The IUCN Red List classifies Electrophorus electricus as Least Concern, and Volta’s electric eel is also listed as Least Concern. All three species have large ranges in remote river systems. Local threats include dams, mining, river pollution and forest loss in the Amazon and Guiana regions.

Electric eels and people

Electric eels have fascinated scientists for centuries. In the 1770s, the surgeon John Hunter described their electric organs, and experiments on electric eels and torpedo rays influenced Alessandro Volta, who built the first electric battery in 1800. In 1800, the explorer Alexander von Humboldt described people in Venezuela driving horses into a pool so that electric eels would leap and shock them until the eels were exhausted. Many doubted the story, but in 2016 Catania showed that electric eels really do leap out of the water to press their chin against a threat while discharging. In 1839, Michael Faraday used a captive electric eel to prove that its shocks were true electricity.

Electric eels remain important in research. Their electric organs supplied the material for the first sequencing of the voltage-gated sodium channel, a protein that lets nerve and muscle cells fire, and engineers study electrocytes as models for soft, flexible batteries.

For people, the main risk is touching or stepping near a large eel in shallow water. Shocks are very painful and can make muscles spasm, but documented deaths are rare. Electric eels should be watched from a distance and never handled. If someone is shocked, seek emergency medical help immediately: call 911 in the US, 112 in the EU or 999 in the UK.