The electric eel is the closest thing nature’s got to a living, breathing battery.
Running up to eight feet in length, these serpentine swimmers (which actually aren’t true eels, but a type of knifefish) are packed with thousands of cells that can generate their own electricity. Some of their homemade jolts are low-voltage, radar-like pulses that help the fish navigate. When prompted, however, electric eels can also serve up shocks powerful enough to incapacitate a horse.
Beneath this electrifying exterior, things get even funkier. Unlike most other fish, electric eels don’t rely on their gills to breathe, instead periodically peeking above water to suck air into their lung-like mouths. During the dry season, females will lay thousands of eggs into nests forged out of their mates’ saliva. And—because DIY electricity just isn’t enough—when they’re f(eel)ing threatened, these suckers can launch themselves at attackers to deliver targeted parcels of pain.
There’s a lot that makes the electric eel unique. And for centuries, scientists thought they all comprised a single species—Electrophorus electricus—occupying its own lonely branch on the knifefish family tree. But it turns out electric eels harbor quite the shocking secret: These fish are so nice, they speciated twice.
An international team of scientists has found that at least three species of electric eel slither the rivers of South America. One of them, Electrophorus voltai, packs an unexpectedly powerful punch, discharging shocks up to 860 volts. That’s a 30 percent uptick over the previous record—and a stat that earns E. voltai the title of the strongest known living source of electricity.
“That’s bonkers,” says Kory Evans, an evolutionary biologist who studies electric fish at Brown University, but was not involved in the study. “The fact that there’s a living organism that has the ability to generate this kind of violent electricity is really shocking, no pun intended.”
The study, published today in the journal Nature Communications, triples the membership of the genus Electrophorus, which now includes the OG E. electricus, as well as newcomers E. voltai and E. varii. (Does this make electric eels less special? Maybe it boosts their appeal by a factor of three.)
In truth, though, the discovery has been a long time coming. Since their discovery in 1766 by Swedish zoologist Carl Linnaeus, electric eels have been found all over Greater Amazonia, lurking wherever the water’s fresh, calm, and chock full of invertebrate snacks.
That’s an enormous range for a single species—essentially the top half of a continent, Evans says. Animals that spread into such diverse geographical regions tend to split off into separate species, especially if disparate groups lose contact with one another along the way. That should have been the case for electric eels, which, with their penchant for shallow, slow-moving waters, aren’t exactly the most cosmopolitan of fish.
Researchers have been trying to “break up” E. electricus for years, says Evans, who praised the new paper. “My first thought was, ‘Oh, they finally did it!’”
There’s a few reasons it took 250 years to get to this point, says study author David de Santana, a zoologist and fish biologist at the Smithsonian’s National Museum of Natural History. For one, the trio of species his team teased apart all look remarkably similar, save for a few subtle discrepancies, like the shapes of their skulls. Even now, with three clear-cut bins to sort them into, picking apart their physical differences takes an exacting eye. According to de Santana, who studies fish morphology for a living, “this was my hardest work yet.”
The crux of the matter came down to a combination of intensive field work and modern genetic sequencing. De Santana and his colleagues spent the better part of four years traipsing through the river basins of Greater Amazonia, wrangling fish out of muddy streams, swamps, and plains throughout Brazil, French Guiana, Guyana, and Suriname.
Back in the lab, DNA extracted from 107 specimens revealed three distinct groups of animals. While the trio appear to share a common ancestor, they ultimately split from each other in two bouts: once about 7.1 million years ago, when E. varii branched off, and again 3.6 million years ago, when E. electricus and E. voltai went their separate ways.
Nowadays, the three species don’t have much to do with one another. While E. electricus was once thought to dominate the entire Amazonian region, de Santana’s team has narrowed its range to the Guiana Shield, a northerly geological formation home to highlands with rapids and waterfalls. South of this is a similar region called the Brazilian Shield, which appears to be the main stomping grounds of E. voltai. De Santana thinks the fast-flowing waters may have helped shape the two closely-related species’ relatively flat heads.
The geographic outlier of the bunch, then, is E. varii, a more bulb-headed fish that lurks in the lowlands of the Amazon Basin, where the waters are murky and sluggish.
Not to be outdone, E. voltai managed to distinguish itself in its own way. When the researchers hooked electrodes up to some of the fish to suss out their shock factor, one E. voltai specimen managed to pump out a whopping 860 volts of electricity.
The team only hooked six fish up to their oscilloscope, and de Santana suspects researchers have yet to crown the world’s most electrifying eel. (De Santana, who’s received his fair share of shocks, adds that the jolts are brief, and “not so bad.” That said, you would not want to get cornered by a dozen or so pissed off electric eels at once—a real concern, considering the team believes the fish sometimes hunt in packs.)
It’s still not totally clear what originally drove the three Electrophorus species apart, de Santana says. But his team is now hard at work disentangling more of the differences that exist between them—and it’s very possible that a few more species have yet to be uncovered.
Evans suspects the new species designations won’t slither down smoothly for everyone. “Usually when you split up species...it gets controversial,” he says. “But genetically, [these electric eels] sort out nicely, and it’s hard to argue with that.”
Kate Allen, a neuroscientist and fish biologist at Johns Hopkins University who was not involved in the study, agrees, pointing out that at least 250 species of electric fish exist in South America (though Electrophorus are the only ones that weaponize their zap). “It’s kind of weird that there would only be one species of electric eel given the diversity in the rest of their group,” she says.
Regardless of where species lines are drawn, though, simply having a more comprehensive catalog of these funky fish could be a boon for scientists in a variety of fields, de Santana says. Electric eels inspired Italian physicist Alessandro Volta to design the first battery in 1799; centuries later, researchers are still studying them to develop more efficient power sources. Other Electrophorus aficionados are exploring applications in the treatment of neurodegenerative disease, or designing robots modeled on the fish’s elongated anal fin, which allows it to swim backward or forward, or simply hover in place.
For these reasons and more, de Santana stresses the importance of preserving biodiversity in the Amazon, where thousands of fires currently rage amidst widespread deforestation. The electric eels’ species surprise, he says, is just the latest piece of evidence that many of the region’s biological riches remain unexplored.
After all, there’s nothing more conspicuous than an 8-foot-long electric eel leaping out of the water to shock you, Allen adds. If we’re still finding diversity “in such a big, charismatic species,” she says, “that means there’s a lot out there we don’t yet know about.”