The incapacitating 600-volt zap of electric eels serves dual functions: Not only does it act like a Taser, it’s also simultaneously a high-precision tracking device for targeting fast-moving prey. The findings are published in Nature Communications this week.
Last year, we learned that these badasses can remotely control their prey through water. Vanderbilt University’s Kenneth Catania and colleagues showed that the eels produce a variety of electric discharges that range from lower-voltage ones used for searching to high-voltage strikes that allow them to hijack the nerves of their prey – temporarily immobilizing them and preventing escape. The electric eel’s high-voltage discharge has been known to be a weapon for centuries, but its sensory role – for electroreception – has been overlooked. How do they quickly locate prey that they’ve successfully immobilized?
For this new study, Catania presented four Electrophorus electricus eels with anaesthetized fish that were artificially made to twitch when a current passes through their bodies – simulating the movement of real, live prey to elicit an eel attack. Sometimes it was just a fish; other times there was a fish and a conductive carbon rod. Discharges from the eels’ electric organ were recorded using electrodes in the water, and recordings of eel behavior were made using high-speed video camera.
An eel’s strikes, Catania found, are accurately guided by continual sensory feedback from the high-voltage discharge. When all other sensory cues were excluded – visual, chemical, and mechanosensory (for mechanical stimuli, such as a touch) – the eels strike at the fish only when there’s an electrical conductor.
Fish twitch elicited high-voltage, high-frequency volleys that guided the violent suction-feeding attempt (directed at the conductor, in this case). All this happens within seconds (see video below). Meanwhile, strikes initiated when there were no conductors had to be aborted: Since eels modify their strike trajectories using conductor location, they’d miss their target when feedback from electrical conductors is absent.
That the eel’s high-voltage discharge is a sensory system and a weapon at the same time indicates that the predatory behavior of these sensory specialists is far more sophisticated and formidable than we previously thought.
Video credit: Kenneth Catania