For the first time, electric eels are seen hunting and breaking prey as a group

Apparently electric eels were not the loners we thought they were.

In a small deep lake in the Amazon River basin in Brazil, scientists have for the first time recorded the fish not only living together, but actively working together to supply, and to bring down the prey.

There is even evidence that the strategy is working. Of the plentiful electric eels Volta (Electrophorus voltai, not a real eel but a type of knife) was found living in the lake, many of which were over 1.2 meters (4 feet) long and thrived.

“This is an amazing discovery,” said ichthyologist Carlos David de Santana from the Smithsonian Institution’s National Museum of Natural History. “Nothing like this has ever been recorded in electric eels.”

Little is known about Volta’s electric eel. The fish was only recently found in a lake beside the Iriri river, and was officially described and recognized as a unique species last year. But it packs a punch, capable of releasing a single shock above 860 volts – more powerful than any other electric eel recorded.

De Santana and his team saw the electric eels hunting in a group in 2012. More than 100 people seemed to work together to kill and kill a prey so that the whole squad could catch food. But one observation was not enough to classify the hunt as normal behavior.

In 2014, the team returned and found even more Volta electric eels, so they had to work watching and recording the animals. Over 72 hours of continuous observation, they saw the electric eels engaged in five additional hunts. Not only was this enough to classify the behavior as usual, it allowed the researchers to observe and record exactly how these “social predation events” occur.

During the day and night, the eels were mostly at rest. At nightfall and early morning hours, the electric eels woke up to hunt. This, the team noted in their paper, is unusual: Volta ‘s electric eels are usually only seen foraging at night and alone.

The difference here is remarkable. At each time, more than 100 individual electric eels gathered and began to swim in circles, effectively herding smaller groups of fish, usually characters, into a “ball of prey”. gradually entering deeper waters.

Then, once the predator was tightly charged and had nowhere to go, up to 10 of the electric eels moved forward and launched a powerful strike, surprising the prey – to jump out of the water before falling back down, meaningless.

“If you think about it, an individual of this species can emit up to 860 volts – so in theory if 10 of them are released at the same time, they could be produces up to 8,600 volts of electricity, “de Santana said.” That’s about the same voltage needed to power 100 light bulbs. “

As soon as the prey was caught, the squad was able to move in and eat at leisure.

Each hunt, found by the team, took about an hour and involved five to seven electric strikes.

“Group hunting is very common among mammals, but it is very rare in fish,” de Santana said. “Only nine other fish species are known to do this, which makes this discovery very special.”

Nevertheless, while the shootings may be normal, the team still believes they could be very rare. In their interviews with locals, the congregation of electric eels and hunting behavior were not mentioned. Therefore, whether the electric eels congregate to hunt or go alone may depend on the right conditions, such as high prey abundance, and special areas with plenty of shelter for large numbers of fish. sin.

Although little is known yet, the team believe that the eels return to the lake every year. They have launched a citizen science project called Projeto Poraquê, where locals can record ideas; these data could be extremely useful. And the team plans to return to the place where they hope to see the animals again.

“As well as trying to find more numbers of eels that are involved in group food, our future laboratory and laboratory-based studies will examine social predation. in electric eels with a focus on the connection between population, social structures, genomics, and electrogenesis, ”they wrote in their paper.

“In short, this case offers an unparalleled perspective for future studies of the evolutionary interplay between predatory tactics and escape among spines.”

The research was published in Ecology & evolution.

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