Electric eel is apparently not the loner we thought.
In a small lake deep in the Amazon River basin in Brazil, scientists have recorded for the first time that the fish not only live together, but also actively cooperate to feed and to drop their prey.
There is even evidence that the strategy works. Some of Volta’s abundant electric eels (Electrophorus voltai, not a real eel, but a kind of knifefish) found in the lake, was much more than 1.2 meters long and flourishing.
“This is an extraordinary discovery,” said physiologist Carlos David de Santana of the Smithsonian Institution’s National Museum of Natural History. “Such a thing has never been documented in electric eels.”
Not much is known about Volta’s electric eel. The fish was only recently discovered in a lake along the Iriri River, and was officially described and recognized as a distinct species last year. But it has a stroke that can discharge a single shock of more than 860 volts – more powerful than any other electric eel recorded.
De Santana and his team first observed the hunt for electric eels in a group in 2012. It seems that more than 100 individuals work together to herd and kill prey so that the whole can feed lean. But one observation was not enough to classify the hunt as normal behavior.
In 2014, the team returned and found even more Volta’s electric eels, so they had to go to work observing and recording the animals. Over 72 hours of continuous observation, they saw the electric eel doing five more hunts. Not only was this enough to classify the behavior as normal, it enabled the researchers to observe and record exactly how these “social predation events” occur.
During the day and at night, the electric eels mostly rested. At dusk and dawn, the twilight hours, the electric eels stirred themselves to hunt. This is unusual according to the team in their paper: Volta’s electric eels are usually only fed at night and alone.
The difference here is striking. On each occasion, more than 100 individual electric eels gathered and began swimming in circles, effectively training groups of smaller fish, mostly carasins, into a ‘prey ball’ that gradually fed them into shallower waters.
Once the prey ball was nowhere to go, up to ten of the electric eels moved forward and launched a powerful joint strike, stunning the prey – which would jump out of the water before falling senseless again.
“If you think about it, an individual of this species can produce a discharge of up to 860 volts – so in theory, if ten of them are discharged simultaneously, they can produce up to 8600 volts of electricity,” de Santana said. . “It’s about the same voltage needed to power 100 light bulbs.”
Once the prey was anesthetized, the scale could retract and feed at ease.
The hunt took every hunt, and it lasted about an hour and involved five to seven electrical attacks.
“Hunting in groups is fairly common among mammals, but it is actually very rare in fish,” de Santana said. “There are only nine other species of fish that do this, which makes this finding really special.”
Nevertheless, although the hunt may be normal, the team still believes it could be quite rare. In their interviews with locals, the congregation and the hunt for the electric eel were not mentioned. Whether the electric eel gathers to hunt or go alone may depend on the right conditions, such as a large prey abundance, and specific places with plenty of shelter for a large number of these fish.
Although many are still unknown, the team believes the electric eels are likely to return to the lake annually. They have launched a civil science project called Projeto Poraquê, where locals can record observations; this data can be invaluable. And the team plans to return to the site in hopes of observing the animals again.
“In addition to trying to detect additional populations of eels involved in group feeding, our future field and laboratory-based studies will investigate social predation in electric eels, focusing on the relationship between population, social structures, genomics and electrogenesis,” they wrote. in their newspaper.
“In short, this case provides a unique perspective for future studies on the evolutionary interaction between predation and escape methods among vertebrates.”
The research was published in Ecology and evolution.