How an Electric Eel Is Like a Taser

For the past few weeks, the Science Friday Book Club has been reading The Lost City of Z, by David Grann, in which a number of Amazonian creatures make an appearance. One is the notorious electric eel. Read on to learn more about how the species shock its prey:

The first thing you need to know about the electric eel, pictured above, is that it isn’t actually an eel. Despite its moniker, the South American creature Electrophorus electricus is a fish—the only species in its genus—and more closely related to other electric fish than to eels, according to Kenneth C. Catania, the Stevenson Professor of biological sciences at Vanderbilt University.

Its electrifying abilities are real, though. Research by other scientists has shown that the species can emit upwards of 600 volts—about five times the voltage of a standard U.S. wall socket—to hunt and debilitate prey. In December, Catania became the first to describe how the fish’s complex electroshock system affects its food, publishing his findings in Science.

Catania began by filming electric eels in an aquarium as they interacted with prey (typically other fish) and then watched the footage in very, very slow motion. “A lot of predators move really fast,” he says, and this one is no exception. After reviewing the recording at 1,000 frames per second, he found that the fish was able to completely immobilize its victims in just three milliseconds.

“That’s 3,000ths of a second,” he says. “So that raises the question of, How could the eel be doing that?”

Through further experimentation, Catania found that the animal’s shock works like a Taser, that infamous electrical weapon. A Taser can deliver 19 high-voltage pulses a second, which overwhelm a person’s motor neurons, causing involuntary muscle contractions. An electric eel, meanwhile, can administer 400 high-voltage pulses a second, according to Cantania—a volley of discharge that temporarily immobilizes a victim before the predator even touches it. “It’s really remotely controlling the motor neurons of the prey,” says Catania.

The sinewy fish delivers those pulses using electric organs, which are essentially modified muscles that act “like batteries in a flashlight,” says Catania. Those muscles take up most of the room in its body, which can grow longer than eight feet. (The other internal organs are compacted within the first six inches or so of its front end.)

Cantania also found that when it’s hunting, the electric eel continually sends out low-voltage pulses in a manner similar to other electric fish, perhaps as a means of sensing its environment. When it detects food nearby, it amps those signals up to what Cantania calls “doublets.” These are two high-voltage pulses, spaced about two milliseconds apart, that are strong enough to make potential prey in the fish’s wake twitch their muscles.

“[The electric eel] causes the prey to make a movement stronger than they could even voluntarily make if they wanted to make the biggest movement ever,” says Catania. “It’s the worst thing that could possibly happen to you [as prey].” Indeed, electric eels are extremely sensitive to water movements, so any twitching is enough for the predator to immediately zero in on its victim. And then, “it basically follows up with the full volley and attacks the side of the water movement and eats whatever is there,” says Catania.

If you find yourself near Amazonian waters, where the electric eel makes its home, should you worry? Catania hasn’t heard of any reports of the fish killing or permanently injuring a person. Having been shocked a few times after putting his hand in the wrong place at the wrong time, he likens the feeling to that of walking into an electric fence. “It’s not something you would keep doing,” he laughs.

But being immersed in water could increase the risk of death. “I wouldn’t want to be swimming next to [an electric eel], because if you were immobilized, you could drown,” he says. “I’m sure it would be unpleasant.”

*This article was updated on January 29, 2015, to reflect the following change: “Research by other scientists has shown that electric eels can emit upwards of 600 volts—about five times the voltage of a standard U.S. wall socket.” The article originally stated that 600 volts is equivalent to the power coming out of a standard U.S. wall socket. Voltage and power are not equivalent.