The Electric Eel Hijacks Its Prey's Nerves

Kenneth Catania, a biologist at Vanderbilt, dropped a koi into a tank with an electric eel and turned on a camera that ran at 1,000 frames per second. The eel did three different things with its 600-volt organ. First it released a pair of brief pulses — a doublet — and waited. If a fish was hiding in vegetation, it twitched on the first pulse, locating itself. Then the eel fired a much longer volley, around 400 pulses per second, and the koi froze in mid-water as if it had been switched off.

The twitch and the freeze were not the same effect at different intensities. They were two different attacks on the same target: the prey's motor neurons. Catania showed this by injecting fish with curare, which blocks the nerve-to-muscle handshake. Curare-treated fish ignored the eel's pulses entirely. The shock wasn't paralyzing muscle directly; it was making the prey's own nervous system fire muscle commands the prey hadn't sent.

The doublet works because vertebrate motor neurons fire one twitch per stimulus up to a point. One pulse equals one twitch; two pulses equal two twitches. A frozen, hiding fish that twitches twice in 50 milliseconds has just betrayed itself acoustically, mechanically and electrically. The eel attacks within 20 ms.

The long volley — what Catania called the high-frequency stun — pushes the motor neurons into tetanus, the locked-on state where the muscle can't relax between signals. The fish doesn't pass out. It just can't move while the eel swallows it.