Electric eels, catfish, and rays deliver painful and terrifying shocks.

The Shocking Story of Electric Fish

The Shocking Story of Electric Fish

Wild Things
Slate’s animal blog.
Jan. 6 2015 10:36 AM

The Shocking Story of Electric Fish

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The genome of the electric eel was sequenced in 2014, the culmination of centuries’ worth of exceedingly painful research.

Courtesy of Michigan State University

Zeb Hogan had always kind of wanted to get shocked by an electric eel.

“Not in the daredevil kind of way,” he clarified, but as a matter of curiosity. Hogan is an aquatic biologist and host of a show on Nat Geo Wild called Monster Fish. He’s had his hands around myriad creatures most of us only know from legend, lore, and YouTube.

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In a recent episode, Hogan and his team went to Brazil to look for electric eels in tributaries of the Amazon River. Traditional fishing methods failed to yield any of the creatures, so they turned to another approach, a fish trap constructed of fencing, nets, and a funnel. After a day of waiting, even that wasn’t working, so the whole crew hopped into the thigh-high water to pack up the trap.

“All of a sudden, we heard one of the cameramen yelling,” said Hogan.

The man was shaking, screaming, and clearly in pain. Everyone rushed over to check on him. There was no blood, no sign of attack by piranha or stingray or catfish, and yet even minutes later he was disoriented and confused about what had happened.

And then they realized: There were eels in the water after all.  

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Sharks can be dangerous creatures, but only if you get near their mouths. Same with snapping turtles and Nile crocodiles. Tigers have claws, scorpions their stingers, and snakes their fangs, but in every instance, these animals can only harm you if they can touch you.

Not so with the electric eel (Electrophorus electricus), which is actually not an eel at all but a knifefish.

From the time it’s a tiny larva, the electric eel can generate a few dozen millivolts. As the animal grows, so does its zing. Full-grown adults can reach more than 8 feet in length and are capable of discharging around 600 volts into the water around them. Human deaths by electric eel are extremely rare, but that kind of power does have the potential to arrest the heart or cause respiratory failure. To fully understand this animal’s mayhem potential, just watch this amazing video of a caiman getting cranked by an eel.

Of course, it’s not as if electric animals are playground bullies, discharging their wrath indiscriminately. Their powers are used instead to sense the environment around them, communicate with their own kind, stun prey, and dissuade predators. A recent study even revealed that some eels can use their electricity to Jedi–mind-trick their prey out of hiding.

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Now, imagine what it must have been like for an early human to encounter one of these fish or any of the numerous species of rays and catfish with similar powers: There’s no flash of light. The creature makes no sound. And yet the animals are clearly capable of walloping anything that wanders too close. This is a powerful and ancient magic.

“Three or four hundred years ago, electricity was literally considered to be an occult force,” said William Turkel, associate professor of history at Western University.

And though they did not understand how electric fish produced this energy, people were quick to try to harness it.

In his book Spark from the Deep, Turkel explains how the Romans applied live electric rays (also called torpedoes) to patients as a remedy for gout and headache. Nigerians reportedly dropped colickey babies into tubs containing several live electric catfish. And up until at least 1661, the repeated shock of a torpedo was said to cure even the most stubborn case of prolapsed rectum or uterus.

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“Like many past medicinal treatments, you have to wonder if the cure was preferable to the ailment,” said Turkel. (No, Bill, I don’t think I do.)

But oh, it gets worse. As is often the case with early medicine, some of the participants in the studies of electric fish were not what you would call willing.

You’ve no doubt seen the videos of policemen standing arm-in-arm and then collapsing in unison to demonstrate the power of a Taser. Well, they used to do the same thing in colonial times, only the policemen were slaves, and the Taser was an electric eel, and the whole thing was a lark for the audience.

In another of Turkel’s examples, a young slave boy with crooked arms and legs was tossed daily into a tub with a large electric eel. Sometimes, he was able to crawl out of his own volition, though often someone else would have to haul the boy out of the water (and get shocked in the process). The treatment failed to straighten his shinbones.

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Remember how ol’ Zeb Hogan sorta-kinda-maybe wanted to feel what it was like to get shocked by an eel?

“As the trip went on, I stopped feeling that way,” he said.

At one point during the show, Hogan and company visited a nature reserve so that they could catch an eel and measure its voltage. They had the animal corralled on a tarp and were handling it while wearing thick rubber gloves, but the eel was so powerful Hogan said he could feel a pervasive tingling sensation coming through.

“That was enough to set off alarm bells in my subconscious,” said Hogan. “It made me think, ‘This is something that I shouldn’t be doing.’ ”

Unfortunately for the electric fishes, the power they evolved to keep us away only drew us closer. In the 1700s and 1800s, humans became entranced by experiments with eels, rays, and catfish. The only problem was the animals were, literally, difficult to get ahold of.

One exhaustively named Prussian naturalist, Friedrich Wilhelm Heinrich Alexander von Humboldt, came by his test subjects by way of indigenous peoples in the Caribbean, but at great cost. To catch the eels, the Guayqueria Indians would drive 30 or so mules and horses into a pool at the river’s edge. All those thrashing hooves drove the eels out of the mud and up to the surface, whereupon they set to shocking the ever-loving hell out of the horses and mules.

It’s difficult to say which animals got the worst end of the deal here. After a time, the eels wore themselves out and were able to be drawn out of the water with small harpoons. However, by then many of the horses and mules had been zapped so thoroughly that they disappeared beneath the water’s surface and drowned.

Things didn’t get much better for the electric animals back at the lab. Dissections of every sort were carried out in order to understand where the electricity was coming from.

In the electric catfish of the Nile, the charge was traced to a pair of nerves that could be exposed with a single incision. This made the fish particularly useful in experiments, as opposed to the electric eel, which needed hundreds of such nerves across the length of its body to discharge its payload.

And this is where things get really weird.

In 1780, Luigi Galvani discovered that if you expose the sciatic nerves of a frog leg to static electricity, the leg would kick. (It had to be a frog, by the way. Toad legs twitched too much on their own and made for unreliable measurements.) For many decades after his discovery, a frog leg in a glass tube would remain the most sensitive electricity sensor in science. Fun fact: If you touch one of these sensors against the heart of a living animal, the frog leg will kick in rhythm with the heart’s beat.

For all of these reasons, frog legs were crucial tools in teasing out the secrets of electric animals. Turkel catalogs pages and pages of these bizarre stops and starts—electric rays connected to dozens of stacks of frog legs, the electric organ of a catfish wired to a phone receiver—but my favorite is called the “frog-alarum” or “frog-interrupter.”

First, you take an electric catfish and pin it to the bottom of its tank with a fish-shaped saddle. The saddle both keeps the animal in place and collects its electricity using tin foil at both ends. A pair of wires runs from the catfish to a galvanometer to measure the fish’s charge, then on to a freshly amputated frog leg attached to tiny hammer next to a bell. Then you put a loach in the tank, and wait for the electric catfish to strike.  

Before the frog-alarum, a scientist would have to sit beside the tank for hours on end so as not to miss any action. But now, thanks to this ghastly precursor to Mouse Trap, every time the catfish let out a shock, the bell would ring.

And ring and ring and ring. Poor loach.

Eventually, an invention called the Leyden jar would replace electric animal lab instruments. The new technology was a whole lot easier to care for and transport than a 9-foot fish that coughs up lightning bolts when it’s cranky.

“Of the fish I’ve dealt with, the electric eel is the most obviously capable of inflicting harm,” said Hogan. And that means a lot coming from a guy who routinely goes looking for giant stingrays, alligator gar, and Mongolian terror trout.

The good news, Hogan said, is that most electric animals want nothing to do with humans. Even the fishermen Hogan talked with, guys who have spent their whole lives on the Amazon River, had only a handful of electric eel encounters between them.

So as long as you aren’t a documentary filmmaker or a 19th-century electrophysiologist, you should be just fine.