Scientists surprised to find that electric eels sometimes hunt in packs

Volta's electric eels can gather in groups, working together to corral smaller fish in shallower waters, a new study finds. Then, smaller groups of about 10 eels attack in unison with high-voltage discharges.

Electric eels were long believed to be solitary predators, preferring to hunt and kill their prey alone by sneaking up on unsuspecting sleeping fish at night and shocking them into submission. But according to a recent paper published in the journal Ecology and Evolution, there are rare circumstances in which eels employ a social hunting strategy instead. Specifically, researchers have observed more than 100 electric eels in a small lake in the Brazilian Amazon River basin forming cooperative hunting parties to capture small fish called tetras.

"This is an extraordinary discovery," co-author C. David de Santana, of the Smithsonian National Museum of Natural History, said. "Nothing like this has ever been documented in electric eels. Hunting in groups is pretty common among mammals, but it's actually quite rare in fishes. There are only nine other species of fishes known to do this, which makes this finding really special."

Electric eels are technically knife fish. The eel produces its signature electric discharges-both low and high voltages, depending on the purpose for discharging-via three pairs of abdominal organs composed of electrocytes, located symmetrically along both sides of the eel. The brain sends a signal to the electrocytes, opening ion channels and briefly reversing the polarity. The difference in electric potential then generates a current, much like a battery with stacked plates.

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