Electric eels are puppet masters

New Scientist pulls back the curtain on how electric eels “remote control” their prey, freezing them right next to their hungry mouths:

The experiments that untangled these mechanisms were devised and run by Kenneth Catania at Vanderbilt University in Nashville, Tennessee. In a natural environment, Catania watched an eel hunting and measured its electric discharges. As the eel was poised to strike, it emitted a barrage of high-voltage electric pulses. This stopped the fish in its tracks, allowing the eel to catch it easily.

To work out what was happening, Catania anaesthetised fish, removed their brains, and dangled them behind an electrically permeable agar barrier in an eel tank. Worms were then put into the tank for the eels to feed on, and the electric zaps sent out to catch the worms also reached the fish.

After about 3 milliseconds, the fish’s muscles completely contracted.

A chemical injected into another brainless fish to stop its motor neurons working, and another fish with its spine removed helped to complete the picture: the electric shock makes the motor neurons fire and contract the muscles, and it happens without the need for the central nervous system.

Catania also discovered that a different, high-voltage, two-pulse signal fired out by the eel makes a fish within range twitch uncontrollably, giving away its position and allowing the eel to go after it with its conventional attack of series of high-voltage pulses.

This two-pulse signal seems to tell the eel whether possible prey is living when information is limited, such as in murky or rocky environments, where the prey is hidden, the researchers say.