In August 2012, Douglas Bastos, then a graduate pupil at Brazil’s Instituto Nacional de Pesquisas da Amazônia, was exploring a distant waterway within the Amazon rainforest when he got here throughout a small lake teeming with electrical eels.
Electrical eels, which regardless of their identify are literally a kind of knifefish, had been believed to be solitary creatures. And but earlier than Dr. Bastos’s eyes had been greater than 100 of them. Then issues acquired much more jolting.
Dr. Bastos watched, astonished, because the writhing mass of eels started corralling teams of tetra fish into tightly packed balls and bombarding them with synchronized electrical assaults that despatched them flying.
“After I noticed the tetras leaping after the assaults, I used to be in shock,” Dr. Bastos mentioned. “Group looking is a uncommon occasion in freshwater fishes. My first response was to run to the boat and get a digital camera.”
Two years later, Dr. Bastos and researchers from the Smithsonian Nationwide Museum of Pure Historical past returned to the world to review this uncommon phenomenon. The findings of their study, revealed Thursday within the journal Ecology and Evolution, overturn the concept that electrical eels are solely solitary predators and lift new questions in regards to the lives of those little-understood fish.
When the researchers returned to the positioning, alongside the banks of Brazil’s Iriri River, they confirmed that the electrical eels Dr. Bastos had noticed in 2012 had been Volta’s electrical eels, a lately found species that may attain 8 toes in size and are able to producing 860-volt electrical shocks — the strongest electrical discharge of any animal.
For the previous 250 years, scientists believed that each one electrical eels belonged to the identical species, however in 2019, analysis carried out by C. David de Santana, a Smithsonian researcher, proved that there are at least three species, the largest and most electrified being the Volta’s electric eel.
In accordance with Dr. de Santana, a co-author of the brand new examine, no such conduct had ever been documented in electrical eels. “It was fairly sudden,” he mentioned.
Sometimes, electrical eels hunt alone, sneaking up on sleeping fish and stunning them into submission. However looking in teams can allow predators to hunt prey that might in any other case be too quick, such because the tiny tetras. Though many mammals, together with wolves and orcas, are identified to hunt in teams, the technique isn’t employed by fish. Solely 9 species of fish, together with the goldsaddle goldfish, are identified to hunt on this style.
Dr. Bastos and Dr. de Santana analyzed over 70 hours of footage of Volta’s electrical eels conducting extremely coordinated group hunts. At daybreak and nightfall, the slimy, snakelike creatures would congregate in shallow water and begin swimming collectively in massive circles. After corralling hundreds of tiny fish into dense balls, the eels break up off into cooperative looking events with two to 10 members.
These events would then encompass the colleges of terrified tetra and launch joint electrical assaults, sending the tetra leaping out of the water. When the electrocuted fish splashed down, the eels shortly devoured them.
Though the researchers weren’t in a position to measure the voltage of the coordinated electrical assaults, they estimate that 10 Volta’s electrical eels working collectively might create an electrical present robust sufficient to energy 100 gentle bulbs.
The researchers suspect these electrical eels orchestrate their assaults by speaking by way of low-voltage electrical discharges.
Whereas it’s unclear if different species of electrical eels hunt in teams, consultants say it’s not unlikely. “It’s doable that each one electrical eel species hunt cooperatively,” mentioned Kory Evans, a fish ecologist at Rice College.
Dr. de Santana and his colleagues plan on returning to the Iriri River to gather tissue samples from the electrical eels and equip them with radio tags to allow them to decide if familial relation performs any position within the fishes’ cooperation, because it does with different pack hunters. He additionally has plans to gather a few of the eels from the wild so he and his collaborators can study extra about how these animals talk.
“There’s a lot to study,” he mentioned.