Electric Eels Curl Up to Double Their Shock Value

The predators take down difficult prey by curling up their bodies to create a powerful electric dipole field

Electric eels are really shocking biologists. (Norbert Wu/Minden Pictures/Corbis)
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Electric eels are famed for their specialized hunting methods, and now scientists have found out about a particularly stunning tactic.

Normally, these marine predators hunt by emitting high-voltage pulses in rapid succession. Like getting zapped with a Taser, the eels emit such force that it causes involuntary muscle contractions in passing fish, temporarily immobilizing them.

The electric eel then swoops in for the kill, gobbling down its still-living victim.

Sometimes, however, those quick bouts of current aren’t enough to paralyze prey, especially if the electric eel is on the younger and smaller side, or if the fish in question is especially large or unwieldy. That doesn't necessarily mean the eel will go hungry, however.

Kenneth Catania, a biologist at Vanderbilt University who specializes in animals with unusual sensory systems, happened to notice that some of the eels in his lab often looped their bodies around prey. The animals always did so in the same particular way, with the head and tail positioned close together but not touching.

To investigate this behavior, Catania stuck current-measuring electrodes into dead fish and then presented those aquatic treats to his electric eels by dangling them into the aquarium on a wire. When the eels attacked, he tugged on the wire to simulate a struggle.

“I kind of joke that it was my eel chew toy,” he said in a statement. The electric eels eventually curled around the fish to gain control of it, and Catania’s measurements showed that the current they produced in that special position was significantly stronger than what they normally deliver.

As he describes today in Current Biology, eels can at least double their power by curling up so that the two poles of their electric organ—located at the base of the eel’s head and tail—come together. A struggling fish or crayfish sandwiched inside the eel’s embrace experiences the full force of those amplified discharges.

In these clips, an electric eel in the lab attacks a dead fish attached to wire, which is shaken to simulate a struggle. The sounds represent the change in voltage level the eel is producing. (Video courtesy Kenneth Catania)

Catania explored the effect this has on prey using electric pulses that matched the intensity of what he recorded in the curled up eels. He applied the pulses to whole fish and to crayfish tails and found that current of that strength results in profound muscle fatigue and loss of control over contraction.

“Each of these pulses the eel gives off is activating the nervous system of the prey,” he says. “The eel essentially has remote control over the prey’s muscles and runs them to exhaustion, leaving the prey temporarily helpless.”

Catania points out that there was a time when biologists looked down on electric eels as primitive predators that sent out electric fields willy-nilly, hoping to hit a fish victim in the process. The more researchers learn about these exceptional animals’ skills, however, the more they have come to realize that they are actually masters of electrical manipulation.

Indeed, this isn’t the first shocking discovery Catania has made this month. Last week, he published another paper showing that electric eels also use their electric pulses as tracking devices for locating prey. As he delves deeper into the world of electric eels—including investigating questions such as how the eels manage to avoid shocking their own heads when they curl up—more unexpected findings are sure to emerge. 

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