Electric eels' secret weapon: Curl before shocking prey

Young eels curl into a horseshoe shape to double their shock value when incapacitating large, unwieldy prey, according to a Vanderbilt University experiment.

Jason Gallant/Michigan State University/Reuters/File
An electric eel swims through vegetation. Scientists have discovered that young eels curl to unleash a more powerful electric jolt to immobilize prey.

Scientists have found that the electric eel, which zaps prey with a powerful electric shock to immobilize it, also has more sophisticated electrocution techniques up its proverbial sleeves.

Younger eels, who have less shocking power, curl their bodies around prey to double the voltage of their shock, "sandwiching it between the two poles of their powerful electric organ," according to a paper published Wednesday in the journal Current Biology.

This powerful shock incapacitates even very large fish, giving the young predators a chance to release and quickly reposition their unwieldy prey in order to swallow it.

"In my mind, it’s sort of a testament to how even an animal that’s been studied for centuries may be doing amazing things that we were unaware of [until] we look closely," said Vanderbilt University biology professor Kenneth C. Catania, who led the study, to the Los Angeles Times.

Eels' serpentine bodies contain electric organs with thousands of specialized cells that store power like tiny batteries, explains National Geographic. An eel zaps its prey with a Taser-like, 600 volt shock – five times the power of a US wall socket – which causes fish muscles to contract.

Prey become temporarily immobilized, giving the eel time to scoop it up and swallow it quickly, before the prey seize "their last, fleeting opportunity to escape as they are briefly released and repositioned," the scientists say.

But younger eels have much less power, and their Amazonian habitat is home to the world’s most diverse mix of fish, which have different sizes, shapes, and protective features, including spines.

So scientists wanted to know, "What happens when an eel struggles with large prey that may not be easily subdued or swallowed? Or when juvenile eels attack?"

To find out, they stuffed goldfish with electrodes designed to measure shock voltage, and then they fed the goldfish to eels in an aquarium.

They observed young eels curl their bodies like horseshoe magnets, bringing their positive electrical pole (head) closer to their negative electric pole (tail), to amplify their electric strength.

With a doubled shock value, the eels hit their prey with numerous shocks, paralyzing the fish and ensuring a meal.

For Catania, this raises the question of how, with so much electricity flowing through their bodies, do eels avoid shocking themselves?

"How they protect their nervous system and their own brain and their own muscles from being activated — as far as I know, it’s pretty much an open question," Catania told the Times.

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