Eels Work Together as a Group to Hunt Small Fish Tetras

Scientists, led by fish research associate C. David de Santa from Smithsonian's National Museum of Natural History recently discovered a small, river-fed lake filled with over a hundred adult eels in the Brazilian Amazon basin. Many of these eels were said to be upwards of four feet long.

A report posted on Vectors Journal said, "On its own, this was an intriguing discovery, electric eels," a knifefish type, instead of true eels, were believed to be "solitary creatures."

However, in the said lake along the banks of the Iriri River in the state of Para in Brazil, the scientists were able to observe the eels "working together to herd small fish tetras into tightly packed balls."

Then, they witnessed, too, groups of 10 eels, sporadically splitting off to form cooperative hunting groups, unlike packs of wolves or pods of killer whales.

The said smaller groups then hemmed in the prey ball and propelled simultaneous attacks, striking the tetras into submission.

De Santana, the study's senior author, said, this is such "an extraordinary discovery." He added, nothing like this new finding has "ever been documented in electric eels."

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Special Research Finding

According to a Smithsonian e-news report, a new paper describes the said novel behavior in the Ecology and Evolution journal's January 14 issue. The research findings reverse the notion that these serpentine fish are "exclusive solitary predators" and welcome new questions on how much these seemingly "little-understood fish live."

Describing the creatures' behavior, de Santana said, while hunting in groups is somewhat typical among mammals, it is, in fact, unusual and infrequent in fishes.

Only nine other fish species, he added, are known for this practice, "which makes this particular finding really special."

One of the new electric eel species presented in his paper in 2019 entitled, Volta's electric eel or Electrophorus voltaic, has the capability of producing 860-volt electric shocks, the strongest discharge coming from any animal on Earth, and 210 volts higher compared to the previous record.

This newly described Volta's electric eel, which can reach eight feet long, is the same species behind the strategy of social hunting at the center of the new research of Santana.

He explained, if one thinks about it, an individual of this species can generate a maximum of 860 volts for a discharge.

Therefore, he added, "in theory 10 of them discharged simultaneously," they could be generating a maximum of "8,600 volts of electricity." The said number is roughly the same voltage required "to power 100 light bulbs."

Initial Discovery of the Electric Eel Hunting in Groups

De Santana's group initially witnessed Volta's electric eel hunting in groups while they were on a field expedition in 2012. Douglas Bastos, then a Master of Science candidate at Brazil's INPA or Instituto Nacional de Pesquisas de Amazonia, and the first author of the paper, traveled by boat for five days to explore the diversity of Iriri River fish.

Now an INPA scientist, Bastos discovered a small lake directly linked to the Iriri River, and his surprise, the lake held over 100 adult electric eels.

A succeeding trip in 2014 discovered a similarly extraordinary collection of Volta' electric eels in the same location, which enabled Bastos to record the behavior in greater detail and very that it was only a one-time occurrence.

The team was able to log a total of 72 hours in all, of continuous observation of the eels assembling in this area along the Iriri River.

Electric Attacks

With the tetras which the main group trapped, de Santana said, bands of two 10 eels would split and move closer and then inaugurate joint electric attacks on the prey ball.

The electric shocks propelled the tetras flying out of the water, although when they splashed down, these small fish were motionless.

Lastly, the researchers observed the attacking eels, and what the observers described as their compatriots simply picked off their defenseless prey.

Santana said, each dawn or dusk hunting rook roughly an hour and had between five to seven high-voltage attacks. This, he continued, is the only place where such a behavior has been observed, although, at the moment, the researchers think the eels, perhaps, appear every year.

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