A researcher reveals the shocking truth about electric eels

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Kenneth Catania knows just how much it hurts to be zapped by an electric eel. For the first time, the biologist at Vanderbilt University in Nashville has measured the strength of a defensive electrical attack on a real-life potential predator — himself.

Catania placed his arm in a tank with a 40-centimeter-long electric eel (relatively small as eels go) and determined, in amperes, the electrical current that flowed into him when the eel struck. At its peak, the current reached 40 to 50 milliamperes in his arm, he reports online September 14 in Current Biology. This zap was painful enough to cause him to jerk his hand from the tank during each trial. “If you’ve ever been on a farm and touched an electric fence, it’s pretty similar to that,” he says.

This is Catania’s latest study in a body of research analyzing the intricacies of an electric eel’s behavior. The way electric eels have been described by biologists in the past has been fairly primitive, says Jason Gallant, a biologist who heads the Michigan State University Electric Fish Lab in East Lansing who was not involved in the study. Catania’s work reveals that “what the electric eel is doing is taking the electric ability that it has and using that to its absolute advantage in a very sophisticated, deliberate way,” he says.

Electric eels use electric current to navigate, communicate and hunt for small prey. But when faced with a large land-based predator, eels will launch themselves from the water and electrify the animal with a touch of the head.

Using electrical measurements he collected during the eel attacks, Catania came up with an equation to estimate the amount of electric current flowing from the eel into his arm. The electric shock was strongest when the electric eel was farthest out of the water. That makes sense because when an eel is mostly submerged, the majority of the electricity dissipates in the water. As the eel rises out of the water, the only place left for the electricity to flow is into whatever the fish head-bumps (SN Online: 6/9/16).

Catania cannot say, however, whether a leap attack from an electric eel is equally as shocking for all potential predators. Electrical currents travel through an animal more or less effectively depending on its outer layer. The internal resistance, or opposition to electrical current flow, may be different for a human arm than for an animal with scales or fur, like a crocodile or a dog, Catania notes. More research is needed to understand how powerful the shock is for other land animals.

Extrapolating from his experience with a small eel, Catania estimates that a human struck on the trunk by a larger, 1.8-meter-long electric eel might endure a current of 0.24 amperes, or 63 watts of power. That’s about 8½ times as powerful as the zap from a typical law-enforcement Taser gun.