Electric eels, those perilous predators of South America, can unleash a potent electrical jolt to wallop their hapless prey. But this zap is not used merely to stun other fish.
A new study shows that the eels use it to exert a form of remote control over their victims, causing fish that may be hiding to twitch, thus exposing their location, or inducing involuntary muscle contraction to incapacitate their prey.
"Apparently, eels invented the Taser long before humans," said biologist Kenneth Catania of Vanderbilt University in Nashville, Tennessee, who conducted the research published on Thursday in the journal Science.
The study reveals precisely what an eel's zap does to its victim. In laboratory experiments, Catania showed how the electrical discharges remotely activate the prey's neurons, or nerve cells, that control the muscles.
While hunting, the eels periodically give off two high-voltage pulses separated by a two-millisecond pause, causing a massive involuntary twitch in nearby hidden prey, the study found. The eels, highly sensitive to water movements, can detect motion caused by the twitch, learning the other fish's location.
The eel then delivers a full blast of a longer, high-voltage shock to immobilize the prey through involuntary muscle contraction - much like a Taser - enabling easy capture.
"I have spent much of my career examining extreme animal adaptations and abilities. I have seen a lot of interesting stuff, but the eel's abilities are astounding, perhaps the most amazing thing I have ever observed," Catania said.
"After all, they can generate hundreds of volts - that by itself is incredible. But to use that ability to essentially reach into another animal's nervous system and activate their muscles is a pretty good trick," Catania added.
Electric eels, with serpentine bodies and flattened heads, can reach lengths of six to eight feet (1.8 to 2.5 meters), prowling the Amazon and Orinoco river basins. They possess electric organs with specialized cells called electrocytes that serve as biological batteries and can generate an electric discharge of up to 600 volts to subdue prey or defend against predators.
"Although they are not known to kill people, they are capable of incapacitating humans, horses and obviously fish during their electric discharge," Catania said.
Catania said the eels also use electricity in a third way, periodically giving off a low-voltage pulse that seems to work as sort of a radar system for navigating dark and murky water.