Conservation news

Shocking news: There are actually three species of electric eel in the Amazon, not one

  • A mostly nocturnal species found in freshwater habitats in Mexico and South America, the electric eel (Electrophorus electricus) belongs to the knifefish family and is more closely related to catfish and carp than other eels. It was first described more than 250 years ago by Swedish naturalist Carl Linnaeus.
  • But now a team of scientists led by Carlos David de Santana, an associate researcher at the US Smithsonian National Museum of Natural History, has determined that E. electricus is in fact three distinct species.
  • During their work in the field, the researchers used a voltmeter to record a member of one of the newly described species, E. voltai, discharging 860 volts, the highest discharge ever recorded for any animal (the previous record was 650 volts).

There are now three recognized species of electric eel after two new species were described to science in a paper published in Nature Communications this week.

One of the new eel species is capable of generating a shock of as much as 860 volts, the most powerful electrical discharge ever discovered in any known animal.

A mostly nocturnal species found in freshwater habitats in Mexico and South America, the electric eel (Electrophorus electricus) belongs to the knifefish family and is more closely related to catfish and carp than other eels. It was first described more than 250 years ago by Swedish naturalist Carl Linnaeus. But now a team of scientists led by Carlos David de Santana, an associate researcher at the US Smithsonian National Museum of Natural History, has determined that E. electricus is in fact three distinct species.

De Santana and team collected 107 electric eel specimens from different parts of the Amazon in Brazil, French Guiana, Guyana, and Suriname. They then analyzed the specimens’ mitochondrial and nuclear DNA, morphology, ecological data, and voltage discharge to conclude that the eels actually represented three different species.

David Santana looking for electric fish in the National Forest, Amapá. Photo Credit: E. Kuano.

“Their body shape is highly conserved. It has not changed much during 10 million years of evolution,” Santana said in a statement. “Only a few details of their external morphology distinguish them, and only an integrated analysis of morphology, genetics and ecology was able to make robust distinctions between the species.”

During their work in the field, the researchers used a voltmeter to record a member of one of the newly described species, E. voltai, discharging 860 volts, the highest discharge ever recorded (the previous record was 650 volts). Differences in electrical discharge was a key factor in determining that there were two heretofore unrecognized species of electric eel. “We used voltage as the key differentiation criterion,” said Naércio Menezes, a professor at Brazil’s University of São Paulo and principal investigator of the Thematic Project, of which the present study was a part. “This has never been done before to identify a new species.”

E. electricus is now considered to be the species of electric eel that lives in an area of the northern Amazon known as the Guiana Shield, which encompasses the northern parts of the Brazilian states of Amapá, Amazonas, and Roraima as well as Guyana, French Guiana, and Suriname.

E. voltai, named after Italian physicist and inventor of the electric battery Alessandro Volta, can be found in the Brazilian Shield, which stretches across parts of the Brazilian states of Pará, Amazonas, Rondônia, and Mato Grosso. Smaller amounts of dissolved salts make the region’s water less electrically conductive, leading the researchers to theorize that E. voltai responded by developing the ability to produce stronger electrical discharges in order to stun prey and ward off predators.

E. voltai in the Xingu river. An article published in Nature Communications shows that three species of electric eel exist, not just one as previously described, and that one of them produces an electric shock up to 860 volts. The researchers were funded by FAPESP, the Smithsonian and National Geographic. Photo Credit: L. Souza.

The other newly described species, E. varii, was named for zoologist Richard P. Vari, a researcher at the Smithsonian who passed away in 2016. “He was the foreign researcher who most influenced and helped Brazilian students and researchers with the study of fish in South America,” Santana said.

E. varii can be found in the lowland Amazon Basin, where it inhabits turbid rivers with a relatively large amount of dissolved salts. Since this increases the conductivity of the water, the discharges of E. varii don’t need to be as powerful, and indeed they range from just 151 to 572 volts.

Until 2016, reports of electric eels leaping out of the water to shock would-be predators were considered apocryphal. But Kenneth Catania, a scientist at Vanderbilt University in the US, proved that they do in fact leap out of the water in order to press their chins directly against a target and deliver what he calls their “high-voltage volleys.” You can even watch video of an electric eel attack that Catania made during his study.

Santana and team believe that the species diverged twice: first in the Miocene, approximately 7.1 million years ago, when they separated from their common ancestor; and again in the Pliocene, about 3.6 million years ago, when the species we now know as E. voltai and E. electricus emerged.

“The discovery of new electric eel species in Amazonia, one of the planet’s biodiversity hotspots, is suggestive of the vast amount of species that remain to be discovered in nature,” Santana said. “Furthermore, the region is of great interest to other scientific fields, such as medicine and biotechnology, reinforcing the need to protect and conserve it, and is important for studies involving partnerships among Brazilian researchers, and between us and groups in other countries, to explore the region’s biodiversity.”

An electric eel. Photo by Sharon Mollerus, licensed under CC BY 2.0.

CITATION

• Santana et al. (2019). Unexpected species diversity in electric eels with a description of the strongest living bioelectricity generator. Nature Communications. doi:10.1038/s41467-019-11690-z

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