In a fight for their food, electric eels bend their body into an arch, doubling the electrifying shock of their high-voltage pulses and stunning prey into submission. The findings are published in the journal Current Biology.

These slinky creatures are powerful but mostly blind hunters. They use low-level electrical pulses to roam the muddy waters of the Amazon, but when faced with particularly troublesome prey, they will twist into a horseshoe shape to generate a stronger zap of electricity. 

“When the eel curls its positive and negative poles together and sandwiches the prey in between, you get a focusing of the electric field,” said study author Kenneth Catania, a biologist at Vanderbilt University, to Live Science. 

Essentially, the positively-charged head and negatively-charged tail of the aquatic creature acts like an electric dipole field, shortening the distance between the two poles and electrifying their prey.

This is no mean feat: An electric eel can zap its prey at 600 volts, stunning the wriggling creature into paralysis. For comparison, the voltage of an average U.S. wall socket is 120 volts. The eel’s electrifying shock is so strong, it can even knock a horse off its feet. 

This powerful pulse is achieved via thousands of cells in its serpentine body that are lined up like batteries. While individually, each cell only generates about 0.15 volts, stacked together they can stun a prey into submission.

 

^{Image credit: The sequence of events during what Catania calls a "Typical Dipole Attack." Kenneth Catania/Current Biology}

To measure the voltage discharge of the electric eel, Catania inserted electrodes into a dead fish, hooked the fish onto a wire, and dangled the tempting treat in a small aquarium with an eel. Scenarios of varying difficulty were achieved by wriggling the wire to simulate struggling prey. The end result looked like a toy being yanked around for a cat, but instead of a cat, it was an electric eel. 

The electric eel curled on the prey when the struggle became a tad too much. “The amplifying effect of their curling behavior at least doubles the effective power of their discharge through prey compared to an eel in a linear position,” wrote Catania in the paper.

 

^{Image credit: When electric eels change their configuration, it can alter their output of energy. Kenneth Catania / Current Biology}

Electric eels can grow to 2.4 meters (8 feet) in length and weigh 20 kilograms (44 pounds) in weight. Unfortunately, electric eels are not even eels; they are actually knifefish. For videos of their shocking power, check out the author's footage here.

“Given the exceptional power of the electric eel’s discharge, one might wonder why any amplification is needed,” wrote Catania. “But it is important to put this behavior in a larger context. Eels use this tactic when handling large and especially struggling prey that cannot be immediately swallowed.”

This means electric eels likely loop their bodies into a power position when they are smaller and have lower energy output, or when they are large but dealing with prey that have particularly shock-resistant skin.

There’s no doubt the fish’s electric fame is well deserved.