Electric Eels: 860 Volts, Three Species, Not Eels

Until 2019 the electric eel was treated as a single species, Electrophorus electricus, described roughly 250 years ago. A team led by C. David de Santana at the Smithsonian's National Museum of Natural History showed it is three.

The researchers collected and examined 107 specimens and combined genetic, morphological and ecological data, along with 3-D CT scans, to separate them. De Santana has said that without the DNA it would be almost impossible to tell them apart from external features alone. The two new species were named Electrophorus voltai, after Alessandro Volta, and Electrophorus varii, after the late Smithsonian ichthyologist Richard Vari. The work was published in Nature Communications in September 2019.

The three occupy different water. E. varii lives in the slow-flowing lowland floodplains of the Amazon basin. E. electricus is a Guiana Shield fish. E. voltai lives in the highland rivers of the Brazilian Shield and south-flowing rivers of the Guiana Shield.

If you are looking at a photo from an aquarium or a river trip, photograph it and the app identifies it — though as the researchers note, species-level identification in this genus is a laboratory question.

Electrophorus voltai was recorded discharging up to 860 volts, the highest voltage ever measured from a living animal. E. electricus reaches about 650 volts and E. varii about 150.

The explanation researchers offer is water chemistry. Highland waters on the Brazilian Shield have lower conductivity than lowland Amazon floodplain water, so a stronger discharge is needed to push the same effect through them. The highest-voltage species lives where electricity travels least well.

For scale, a standard car battery runs at 12 to 13 volts. What makes the eel survivable to encounter is that the discharge is delivered as brief pulses at very low current, not as a sustained shock — which is why people are hurt by falls, drowning and repeated pulses rather than by electrocution in the usual sense.

An electric eel carries stacked electricity-producing cells along most of its body length, organised into distinct organs that do different jobs.

The Sachs organ produces weak discharges used for navigation and communication. That matters because these are fish of turbid, tannin-stained water where vision is nearly useless; the weak field works as an electrical equivalent of sonar, letting the animal sense objects around it.

Hunter's organ produces the high-voltage pulses used to stun prey and to defend against threats. The two systems run in the same animal and are used for different purposes.

Electric eels also breathe air. They surface to gulp at the water's surface, which is an adaptation to the same oxygen-poor swamps and slow floodplains where the electrical sense pays off.

Treat them as dangerous. A discharge from a large individual is painful enough to cause involuntary muscle contraction, and the real hazard in the water is losing control and drowning, or receiving repeated pulses while unable to get away.

That is not a reason for alarm in North America — electric eels live only in South America, in the Amazon and Orinoco systems and associated floodplains. The practical exposure for most people is a public aquarium exhibit, which is safe by design.

If you are travelling in the Amazon basin, take local guidance on where to swim seriously rather than relying on general advice, and do not handle any eel-shaped fish you cannot identify. Anyone shocked and showing confusion, chest pain, irregular heartbeat or injury from a fall needs medical assessment, not a wait-and-see.

Purely because of shape. An electric eel has a long cylindrical body, no obvious dorsal fin, and a long anal fin running most of the underside that it undulates to swim forwards or backwards — the classic knifefish arrangement.

They belong to the South American knifefishes, and their closest relatives are the catfishes rather than the true eels of the order Anguilliformes. True eels, including morays and the American eel, sit in a completely different part of the fish family tree.

The name stuck for the same reason wolf eel and eelpout did: in English, long-bodied fish get called eels regardless of ancestry. If you want a rule of thumb, a true eel has no pelvic fins and a continuous fin fringe around the tail, while the electric eel's swimming fin is the single long one along the belly.

True eels make up the order Anguilliformes, which Wikipedia divides into 8 suborders, 20 families and 164 genera with about 1,000 species. Electric eels are not among them: they are knifefish that only share the shape. Moray eels alone account for a large share; Sea Dwelling Creatures, a marine livestock wholesaler, puts them at about 200 species in 15 genera.

True eels range from the one-jawed eel at about 5 cm to the slender giant moray at up to 4 m, and the heaviest is the European conger at up to 3 m and 110 kg (Wikipedia).

The main eel families, with their common names (Wikipedia):

• Anguillidae: freshwater eels, such as the American eel, European eel, Japanese eel and short-finned eel, the main commercial species
• Muraenidae: moray eels, such as the green moray, spotted moray, chain moray and California moray
• Congridae: conger and garden eels, such as the American conger
• Ophichthidae: snake eels, such as the sharptail eel
• Synaphobranchidae: cutthroat eels
• Saccopharyngidae: gulper eels
• Moringuidae: spaghetti eels

Fishing database Fishdatabase.com lists 17 eel-type fish recognised by US anglers, mostly morays and congers. Its list also includes the wolf eel and the Asian swamp eel, which, like the electric eel, are called eels without being true eels. See our moray eel and wolf eel pages.

Eels are fish. Wikipedia classifies true eels as ray-finned fish. Several other fish evolved the same long shape independently and are called eels: electric eels, swamp eels, slime eels and deep-sea spiny eels (Wikipedia). None of them is a reptile.

In fish markets and on menus, the freshwater eels of the genus Anguilla are the most familiar: the American, European, Japanese and short-finned eels are the principal commercial species, and Japan eats more than 70 percent of the world's eel catch (Wikipedia). They are also in trouble: Wikipedia lists the European eel as Critically Endangered and the American and Japanese eels as Endangered. On reefs and in aquariums, moray eels are the eels people meet most often.

Because most of their body is a biological battery. The Smithsonian's National Zoo says the three electric organs make up about 80% of the fish's body. Each organ is built from flattened cells called electrocytes, and Wikipedia describes about 6,000 of them stacked in series in the main organ, each producing a small voltage that adds up the same way batteries in a torch add up, for a main-organ discharge of at least 600 volts.

The fish uses that electricity for four jobs, according to the National Zoo: defence, hunting, communication and navigation. Weak pulses let it sense its surroundings in dark, muddy water; strong ones stun prey and drive off threats.

Wikipedia adds that pulses can fire at up to 500 per second, each lasting only about two milliseconds, which is why a shock arrives as a rapid burst rather than a single jolt.

Because the voltage is high but the energy is tiny. Wikipedia gives a maximum current of about 1 ampere at 500 volts per pulse, and a pulse length of about two milliseconds. Multiply those out and one pulse carries roughly 1 joule of energy (500 watts for 0.002 seconds). A 60-watt light bulb uses 60 joules every second.

The fish also runs out. Wikipedia quotes Alexander von Humboldt's 1800 account: after delivering many shocks, the eels needed a long rest and plenty of food before they could discharge strongly again.

The useful part is the design, not the animal. Wikipedia describes synthetic cells modelled on electrocytes, designed by Jian Xu and David Lavan in 2008 as a possible power source for medical implants, and 2016 eel-inspired devices that work as high-voltage capacitors suitable for things like electric watches or LEDs.

The bite is the lesser problem. Wikipedia describes the teeth as small and prickly; electric eels hunt by stunning prey with electricity, not by biting.

The shock is what matters. Historical accounts collected on Wikipedia describe it clearly: John Hunter's 1775 research recorded severe numbness, and Hugh Williamson wrote of receiving a severe shock. Wikipedia also records Kenneth Catania's observation that electric eels will leap out of the water to shock an animal they see as a threat, and Humboldt's account of horses stunned by eels and then drowned.

The practical dangers are the ones already covered above: losing muscle control in water, drowning, falling, and repeated pulses. If someone is shocked and has chest pain, an irregular heartbeat, confusion, breathing trouble or an injury from a fall, get emergency medical help.

No. Treat any water where electric eels live as unsafe for swimming. They live only in South America, and a large one is powerful: the National Zoo gives lengths of 6 to 8 feet, and Wikipedia gives a documented maximum of 2 m and 20 kg.

Two behaviours make them more dangerous than a fish that only shocks when touched:

• Leaping: Catania's work, reported on Wikipedia, shows they can leap from the water to shock a perceived threat
• Group hunting: Wikipedia reports that Volta's electric eel, E. voltai, sometimes hunts in packs, herding shoals of tetras and striking together

Follow local guides in the Amazon and Orinoco basins, stay out of murky backwaters, and do not wade where you cannot see the bottom. In an aquarium, the glass keeps visitors safe.

Figures from the Smithsonian's National Zoo:

• Length: 6 to 8 feet (2 to 2.5 m)
• Lifespan: unknown in the wild; in human care, males typically live 10 to 15 years and females 12 to 22
• Breeding: females lay 1,200 to 1,700 eggs in the dry season; males build nests out of saliva and guard the larvae until the rainy season
• Diet: generalist carnivores that eat fish, crustaceans, insects and small amphibians, reptiles and mammals
• Breathing: obligate air-breathers, with a mouth lined by folded, blood-rich tissue that absorbs oxygen; Wikipedia says they surface for air about every two minutes

A note on voltage: the National Zoo gives "up to 800 volts" for electric eels in general, while the 860-volt figure above is the record for E. voltai. The difference is between a general figure and a single-species record.