One Volta’s electrical eel — in a position to subdue small fish with an 860-volt jolt — is frightening sufficient. Now think about over 100 eels swirling about, unleashing coordinated electrical assaults.
Such a sight was assumed to be solely the stuff of nightmares, no less than for prey. Researchers have lengthy thought that these eels, a sort of knifefish, are solitary, nocturnal hunters that use their electric sense to find smaller fish as they sleep (SN: 12/4/14). However in a distant area of the Amazon, groups of over 100 electric eels (Electrophorus voltai) hunt together, corralling 1000’s of smaller fish collectively to pay attention, shock and devour the prey, researchers report January 14 in Ecology and Evolution.
“That is massively sudden,” says Raimundo Nonato Mendes-Júnior, a biologist on the Chico Mendes Institute for Biodiversity Conservation in Brasilia, Brazil who wasn’t concerned within the examine. “It goes to indicate how very, little or no we find out about how electrical eels behave within the wild.”
Group searching is kind of uncommon in fishes, says Carlos David de Santana, an evolutionary biologist on the Smithsonian’s Nationwide Museum of Pure Historical past in Washington, D.C. “I’d by no means even seen greater than 12 electrical eels collectively within the area,” he says. That’s why he was shocked in 2012 when his colleague Douglas Bastos, now a biologist on the Nationwide Institute of Amazonian Analysis in Manaus, Brazil, reported seeing greater than 100 eels congregating and seemingly searching collectively in a small lake in northern Brazil.
Two years later, de Santana’s workforce returned to the lake to make extra detailed observations. The almost 2-meter-long eels lethargically lay in deeper waters throughout a lot of the day, the researchers discovered. However at nightfall and daybreak, these lengthy streaks of black come collectively, swirling in unison to kind a writhing circle over 100 sturdy that herds 1000’s of smaller fish into shallower waters.
After corralling the prey, smaller teams of about 10 eels unleash coordinated electrical assaults that may ship shocked fish flying from the water. The researchers haven’t but measured the mixed voltage of such assaults, however 10 Volta’s eels firing collectively might, in concept, energy one thing like 100 gentle bulbs, de Santana says. The then helpless, floating prey make simple pickings for the mass of eels. The entire ordeal lasts about two hours.
Up to now, such aggregations have been noticed in solely this one lake. However de Santana suspects that group searching could also be advantageous in different lakes and rivers with giant shoals of small fish. A lot of the eels’ vary stays underexplored by scientists, so de Santana and colleagues are launching a citizen science mission with Indigenous communities to determine extra spots the place many eels dwell collectively, he explains. “There may be nonetheless a lot we don’t find out about these organisms.”