It turns out that electric eels can use their electric pulses to control their prey’s nervous system — activating specific brain cells in fish with different kinds of pulses. And these taser-like pulses don’t just lock muscles in place to keep dinner from swimming away: When prey is hiding, the electric eels can actually use special pulses to make them spasm their way into view.
Vanderbilt biologist Kenneth Catania describes this mechanism in a study published recently in Science.
Catania wanted to study the relationship between electric eels (which, fun fact, are actually fish) and the fish they prey upon with shocks. It’s clear that electric fish are formidable opponents, with pulses that could knock out a horse (really), but just how they use these while hunting hasn’t been studied extensively.
He put his eel subjects under a high-speed camera so he could catch their quick movements. But when he watched the footage, he realized that it wasn’t just their twists and turns that happened so quickly: They could zap and freeze their prey in about 3 milliseconds.
“That was amazing to me, so I had to figure out just how they do it,” he said.
It turns out that the electric eels in Catania’s tank emitted three different kinds of electric pulses. They used low-voltage pulses to sense their environment, and sequences of two or three high-voltage millisecond pulses while hunting. Once they had prey in sight, they used high-voltage, high-frequency pulses to immobilize them.
But these pulses don’t actually act on the muscles of the fish being preyed upon. Instead, they attack specific neurons. Catania confirmed this by injecting some of the prey with curare, a paralytic that works by inhibiting the nervous system. The fish treated with curare didn’t have muscle contractions when they were zapped, indicating that the pulses worked via the nervous system.
In this way, the eel is remarkably like an electric stun-gun.
“In a sense, the eel is using electricity to move into the nervous system of its prey and control the neurons that control their muscles,” Catania said. “It’s giving them a sort of remote control over their prey.”
But it’s those millisecond long pulses sent out during the hunt, which Catania called doublets, that are really interesting. Instead of freezing the fish, these actually cause them to jerk around uncontrollably.
“Eels are incredibly sensitive to water motions, so if the prey is forced to move, the eel can find it,” Catania said. “So they actually have two really remarkable strategies. The eel can cause either complete immobility or a sudden twitch, depending on its needs.”
