Newly Identified 8-foot Electric Eel Delivers Strongest Shock in Animal Kingdom

It isn’t that nobody realized there were huge, dangerous electric fish in the Amazon rivers, just that science thought they were a single species — until now

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Electrophorus electricus.
Electrophorus electricus.Credit: R. Covain

What’s 8 feet (2.4 meters) long, looks like a phallus with psoriasis, can curl up like a bagel, and electrocute you with its nervous system?

Two previously unrecognized species of electric eel revealed by the Smithsonian on Tuesday, that’s what.

The discovery that the electric eels thronging the rivers of South America aren’t a single species with a lot of variation triples the number of recognized electric eel species from one to three, report C. David de Santana and colleagues at the Smithsonian National Museum of Natural History, in Nature Communications.

Electrophorus varii, swimming in the Rio Negro.Credit: D. Bastos

Moreover, the three species appear to occupy different geographical domains, making the zoological confusion over the last 250 years even more remarkable.

“They’re really conspicuous,” remarks de Santana, indicating that he suspects they should have been noticed before now. There is also their pesky predilection for hunting in packs and the fact that they can give you an electric shock you will notice (and then some).

One of the newly recognized species, Electrophorus voltaii, can generate a greater electrical discharge than any other animal: 860 volts. Its name is a tribute to Alessandro Volta (1745-1827), the father of the battery and today’s command of electricity. The “standard” electric eel, Electrophorus electricus, can only generate a pathetic 650 volts. That will stun you too.

The other new species was named Electrophorus varii, after the late Smithsonian ichthyologist Richard Vari.

Electric eel territory in the Amazonia.Credit: Carlos de Santana

The classic eel lives in the waters of the Guiana Shield. The weaker new eel, varii, swims in the rivers of the Brazilian Shield and the monster, voltaii, can be found in the north-flowing rivers of the Brazilian Shield and the south-flowing water of the Guyana Shield.

Among other things, the identification of the new species was based on genetic analysis. The scientists estimate that the species diverged about 3.6 million years ago, when the Amazon flow reversed.

Electric eels aren’t actually eels. They’re a different kind of fish entirely — the Gymnotidae, or naked-backed knifefish. They are popularly called electric eels because from a distance they look like eels.

Electric eels like this environment: Coppename River.Credit: Carlos de Santana

There are no fewer than four suborders of true eels, but none of them can electrocute their prey or attackers. They are just elongated fish with no pelvic fins — and usually no pectoral fins either — that can reach 13 feet in length (in the case of the giant moray eel). The eel has a life cycle that includes a transparent phase, during which they are known as glass eels. They look very pretty in this stage. There is no stage at which electric eels look very pretty.

Electric eels have modified nerve cells organized in special organs that generate electric fields. Their electric charge might not kill, but it can stun and paralzye their prey, which can then be eaten. Or it can stun attackers, which can then be avoided.

And if they stun a fish or frog, and then can’t find the thing because it sank helplessly to the seafloor? Worry not for the electric eel: A report in July explained that the fish — which are, to begin with, largely nocturnal — also uses its high-voltage electric charges as a sensory aid to track the shocked fish. The electrocuted fish twitches, which causes ripples in the water that the eel can detect.

Carlos de Santana going eeling.Credit: E. Kauano

The mechanism by which electric eels generate current was elaborated in Scientific American in 2005. Long story short, the specialized nervous system has the capacity to synchronize electricity-producing cells, which operate in tandem, producing a short-lived current that runs down the eel’s body. The current passes into the water surrounding the animal, causing nasty shocks to anything near it.

If you find yourself attacked by an electric eel, you may perhaps find it a comfort to know that their electrical generation capacity can become fully discharged, at which point it will stop electrocuting you.

It may be less of a comfort to know that these fish seem to be able to communicate and attack in tandem. Electric fish communicate using electrocommunication, and in the case of the naked-backed knifefish, one stimulus leading to communication is being attacked.

Electrophorus voltai swimming in the Xingu River.Credit: L. Sousa

Finally, how does our friend the electric eel (which isn’t actually an eel) generate a current that powerful? They curl up, trying to position the prey fish between their tail and head

“During a typical predatory attack, the eel’s electrical discharge forms a (roughly) dipole field around the eel,” explains Kenneth Catania in an article in Frontiers. “The positive pole is the region around the eel’s head and the negative poll is the region around the tail.” If the fish curls so that the prey fish is between its head and tail, that strengthens the electricity field.

Young electric eels do this every time they hunt. Big adult eels tend to bagel up and blast only when the prey is tough, Catania found.

So if you’re swimming in an Amazonian river and encounter an elongated fish that starts to curl up, you know what to do. Scream.