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More than 200 years after the electric eel inspired
the design of the first battery, it has been discovered that they can
co-ordinate their "zaps".
Researchers working in the Amazon filmed eels gathering in packs to herd
prey, then stunning them with a synchronised electric shock.
"It was really amazing - we thought these were solitary animals," said
researcher Carlos David de Santana.
The discovery is published in the journal Ecology and Evolution.
Douglas Bastos, from the National Centre for Amazonian research in
Manaus, Brazil, filmed the behaviour - capturing the moment of the
collective electric strike. Small fish, called tetras, are the target of
the attack; they fly into the air and land stunned and motionless on the
water.
Dr de Santana, who works at the Smithsonian Museum of Natural History in
Washington DC, was amazed when he saw this behaviour.
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"In my childhood, I visited my grandparents in the Amazon and I
collected fishes in the streams. " he told BBC News. "I've spent 20
years studying electric fishes in the region, but I have never in my
life seen so many adult electric eels together."
As a scientist, Dr de Santana's expeditions into the murky, remote
waters of the Amazon have revealed 85 new species of electric fishes. In
one recent study, he and his colleagues discovered that there are
actually three individual species of electric eel - for 250 years it had
been believed that there was just one.
It is the most powerful of these species that was the subject of this
discovery - Volta's electric eel. The animal is capable of producing an
860-volt electric shock - the strongest electric discharge of any animal
on Earth, and almost four times the voltage from a UK plug socket.
These animals can grow 2m (6ft) in length and are more closely related
to carp and catfish than eels.
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A specialised electric organ exists in each animal's body, which is made
up of thousands of cells called electrocytes that are aligned like
batteries. When triggered, the cells generate a short-lived electric
current that flows along the eels' body.
"These animals are unique," said Dr de Santana. "They use high voltage
discharge to hunt and now [it appears that] they can hunt in social
groups, too.
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"If you look across all the vertebrates - we have about 65,000 species,
and less than 100 engage in social predation."
In recent years, the eels' "biological battery" has inspired the design
of power sources for implanted medical devices, like pacemakers. And
this discovery, Dr de Santana says, shows how much more we have to learn
not only about this species, but about the Amazon and all of its
biodiversity.
"Electric eels' habitats and ecosystems are under immense pressure from
climate change, fires and deforestation," he said.
And while that destruction is happening, this study provides "an example
of how much we still don't know - how many organisms whose life
histories we don't yet understand".
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