Electric eels can remotely control the bodily movements of their prey

© Kenneth Catania

Electric eel (Electrophorus electricus)

Electric eels are badass. Not only can they produce an incapacitating 600-volt zap -- five times that of a U.S. wall socket -- they can also remotely control their prey through water. The predatory eels create a variety of electric discharges that range from lower-voltage ones sent out as environmental sensors to high-voltage strikes that allow them to hijack the nerves of their prey -- immobilizing the muscles and preventing escape. They can even send out short pulses that force the prey to give up their location. The findings were published in this week.

To understand the mechanism of the eel's shocking strike, Vanderbilt University's Kenneth Catania conducted a series of experiments in large aquariums equipped with various detectors. When placed in tanks with delectable fish and worms, the scale-less Amazonian Electrophorus electricus releases pulses of electricity that appear to stun the prey and freeze them in place. Using a high-speed video system, he observed that an eel begins an attack with a high-frequency volley of high-voltage pulses up to 15 milliseconds before striking. In just three milliseconds, the fish are completely paralyzed. They regain mobility after a short period, and they could swim away if the eel doesn't get to them first.

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"I have some friends in law enforcement, so I was familiar with how a Taser works," Catania says in a news release. "And I was struck by the similarity between the eel's volley and a Taser discharge. A Taser delivers 19 high-voltage pulses per second while the electric eel produces 400 pulses per second." To the right is an eel in mid-attack on an immobilized fish.

The electric discharge induces an immobilizing whole-body muscle contraction by activating the motor neurons that control the prey fish's muscles -- and not by controlling the muscles directly. Catania placed two fish behind a barrier: One was injected with saline solution, the other was injected with a paralytic agent that targets the nervous system. The muscles of the fish with the saline solution contracted involuntarily in response to the eel's electrical discharges, but the fish given the paralytic drug showed no contractions.

Furthermore, if the prey is nearby but hiding in rocks or plants, the eel can emit periodic, millisecond pulses of two or three discharges (doublets or triplets) that cause massive muscle twitches. Once the rapid contractions reveal the prey's location, the eel throws down a full, tetanus-inducing volley.

"Normally, you or I or any other animal can't cause all of the muscles in our body to contract at the same time," Catania says. "However, that is just what the eel can cause with this signal."

These high-voltage discharges allow the eels to remotely control the prey's neural pathways by mimicking the normal electrical pulses that the fish's own neurons send to stimulate its muscle movement.