Electric Eel: Most Remarkable Predator in the Animal Kingdom

This behavior had been observed before, but no one had offered an explanation. Catania realized that the maneuver brings the positive pole of the eel’s electric organ, which is located in its head, in close to proximity to its negative pole, located in its tail. By bring the two poles close together, with the prey sandwiched in between, the eel increases the amount electric charge that it delivers to its victim, he realized. So he designed some experiments to measure this effect and found that it more than doubled the strength of the electrical pulses that the prey received.

Like the Taser-like pulses, the strengthened discharges act on the nerves that control the prey animal’s muscles. But Catania’s studies found that the increased power and high pulse rate had an additional effect: It drives the prey muscles so fast and hard that they suffer from profound muscle fatigue.

“The prey animals are completely paralyzed,” said Catania. “The effect is comparable to administering a dose of a paralytic agent like curare.”

Another example of how the eel benefits from this remote control capability is its use of doublets and triplets – short sequences of two or three millisecond, high-voltage pulses that the eels give off while hunting.

It took Catania an extended period of investigation and observation to figure out the purpose of these signals. He finally realized that the pulses were being produced at precise frequencies that induce whole body muscle spasms.

“One of the eel’s major problems is finding prey in the first place,” said Catania. “Their environment in the Amazon is filled with muddy water and all kinds of vegetation that give fish a lot of places to hide. So, as the eel glides along, it emits a doublet or triplet. If there is a fish hiding nearby, then its body will spasm and the spasm will generate pressure waves in the water. Although the electric eels can’t see very well, they are very good at detecting water movement. So this reveals the position of its next meal.”

Catania has also discovered that the eel uses its high-voltage electric discharges as a high-precision radar system that allows it to track fast-moving prey.

For some time, biologists have known that electric fish, in general, and electric eels, in particular, use a low-voltage electric field for navigation. In an article published online by Nature Communications on Oct. 20, Catania reported that the electric eel has a secondary use for its high-voltage electrical system: to track fast-moving prey.

The eel needs a way to keep track of the location of its prey after it is stunned. By designing a series of experiments that preventing the eels from using other sensory cues, Catania showed that the eels used feedback from their high-voltage volleys to zero in on the position of their prey.

“This dual use of the high-voltage system as both a weapon and a sensory system indicates that the eels’ hunting behavior is far more sophisticated than we have thought,” said Catania.