Electric Eels Leap to Deliver Painful, Taser-Like Jolt

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Catania, Stevenson Professor of Biological Sciences, studies the neurobiology of predators and prey and last year proved the validity of a controversial 200-year-old account of eels leaping out of Amazonian waters to shock horses. But documenting their leaping ability left him wondering about the resistances and current for each component of an attack.

Catania realized he had accidentally imitated a predatory attack on his eels in shallow water. But, at first, he was “just confused” by their behavior. Why didn’t they simply swim away? He soon realized the leaping might help the eels to effectively target a would-be predator and intensify the shock.

 

“It was definitely a good lesson in how efficient the electric eel would be at deterring a predator,” said Catania, who worked with a 16-inch-long juvenile eel he affectionately named Finless. “Eels are essentially batteries immersed in water, and I wanted to solve the question of how powerful those batteries are. What’s the internal resistance of the battery? What’s the resistance of the water? My past research left out the last variable: my arm.”

A graphic of the device Ken Catania used to complete the circuit among eel, arm and water. 

Credit: Ken Catania/Vanderbilt University

To close the circuit and get the measurement, he created a device that used copper wire to conduct the electricity from the shock to his arm back to the water, one of the methods documented in his paper “Power Transfer to a Human during an Electric Eel’s Shocking Leap.” It will be published in the Sept. 25 issue of Current Biology.

Catania said the research reminded him that there’s always something more to learn about electric eels, even though they’ve been studied for 200 years.

 

“They’re so much more sophisticated than we possibly could have imagined,” he said. “This animal can generate hundreds of volts, but they’ve also evolved to very efficiently deliver that electricity.”

In fact, electric eels’ leaping behavior had been described by Alexander von Humboldt way back in the 1800s. Humboldt claimed to have witnessed a dramatic battle between electric eels and horses in the Amazon. But, Catania says, “No one really necessarily believed it, or if they did, they thought it was just kind of weird.” Whatever they thought, it was more or less forgotten.

To understand the dynamics of the electrical circuit created when an eel contacts another animal, Catania developed an apparatus to accurately measure the strength of the electric current through a human arm when the electric eels leapt in attack. Catania put that apparatus to use with his own arm and a relatively small, and therefore less powerful, eel.

Credit: Steve Green/Vanderbilt

As reported in the new study, the electrical current delivered by the eel peaked at 40-50 milliamps. That’s more than enough to cause a person or animal considerable pain, but not enough to actually hurt them. In a video, one can see Catania’s arm reflexively pull back, an involuntary reaction similar to what would happen if you touched a hot stove.

“It’s impressive that a little eel could deliver that much electricity,” Catania says. Of course, they have good reason as they may encounter crocodiles, predatory cats, and “who knows what else,” he adds. “We don’t know the main driver of the behavior, but they need to deter predators, and I can tell you it’s really good at that. I can’t imagine an animal that had received this [jolt] sticking around.”

Now that he’s been able to measure the strength of the electrical current, Catania says he can solve the rest of the circuit. That means it’s now possible to estimate the power of a shock delivered by eels of various size or under different circumstances. It turns out the findings are relevant to humans, too. Catania notes that a YouTube video that recently surfaced and went viral shows a fisherman being shocked by a leaping electric eel in the Amazon.

When Catania first saw that footage, it surprised him. But, he now realizes, it’s something that’s “probably happened a lot.” The only difference in the recent case is that someone managed to successfully capture it on video. Now, after voluntarily receiving more shocks in his lab than he cares to recount, Catania has, too. 

Contacts and sources:
Heidi Hall