New observations made near the mouth of a small lake on the banks of the Iriri River in Brazil’s state of Pará show Volta’s electric eels (Electrophorus voltai) herding, encircling shoals of small fishes called tetras, and launching joint predatory high-voltage strikes on the prey ball. The observations, described in a paper in the journal Ecology and Evolution, challenge the idea that electric eels are exclusively solitary predators.
“This is an extraordinary discovery. Nothing like this has ever been documented in electric eels,” said Dr. Carlos David de Santana, a researcher in the Department of Vertebrate Zoology at the Smithsonian Institution’s National Museum of Natural History.
“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.”
First described in 2019, Volta’s electric eels are a species of freshwater fish found in the rivers of South America.
They can reach lengths of 2.4 m (8 feet) and are capable of producing 860-V electric shocks — strongest electric discharge of any animal on Earth and 210 V higher than the previous record.
They are typically observed foraging solo at night, when active prey fish are resting in a somewhat lethargic state in shallow waters.
“If you think about it, an individual of this species can produce a discharge of up to 860 volts — so in theory if 10 of them discharged at the same time, they could be producing up to 8,600 volts of electricity. That’s around the same voltage needed to power 100 light bulbs,” Dr. de Santana said.
He and his colleagues filmed more than 100 adult Volta’s electric eels hunting as a group in a small lake connected with the Iriri River.
“This is the only location where this behavior has been observed,” he said.
“Our initial hypothesis is that this is a relatively rare event that occurs only in places with lots of prey and enough shelter for large numbers of adult eels.”
The researchers hope that their newly-launched citizen scientist program called Projeto Poraquê may help locate more of these special aggregations of eels.
The project, named for an Indigenous Brazilian word for electric eel, will allow users to report sightings and log observations.
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Douglas A. Bastos et al. Social predation in electric eels. Ecology and Evolution, published online January 14, 2021; doi: 10.1002/ece3.7121