The electric eel (Electrophorus electricus) has long been assumed to be one species, but an international team of scientists has now discovered there are actually three separate ones.
The electric eel is the largest species of the order Gymnotiformes, a group of fishes commonly known as the Neotropical or South American knifefish.
There are currently around 250 recognized gymnotiform species among 34 genera and five families. All are capable of producing a weak electric field for communication and navigation.
“The electric eel, which can reach 8.2 feet (2.5 m) in length, is the only fish that produces such a strong discharge; it uses three electric organs. The shock is used for defense and predation,” explained Dr. Carlos David de Santana, a researcher at the US National Museum of Natural History.
Dr. de Santana and his colleagues analyzed genetic, morphological, and ecological data from 107 specimens of the electric eel from across Greater Amazonia.
They found that there is not just one species of the fish but enough differences to recognize three distinct species: Electrophorus electricus from the Guiana Shield, Electrophorus voltaic from the Brazilian Shield, and Electrophorus varii from the lowland Amazon Basin.
“The name of Electrophorus voltaic pays homage to Italian physicist Alessandro Volta, who invented the electric battery in 1799, basing its design on the electric eel,” the researchers said.
“Electrophorus varii is named for Smithsonian zoologist Richard P. Vari. He was the foreign researcher who most influenced and helped Brazilian students and researchers with the study of fish in South America,” Dr. de Santana said.
“During field measurements using a voltmeter, we recorded a discharge of 860 volts, the highest found in any animal, for a specimen of Electrophorus voltaic. The strongest shock previously recorded was 650 volts,” the authors noted.
“We used voltage as the key differentiation criterion. This has never been done before to identify a new species,” said Professor Naercio Menezes, a researcher at the University of São Paulo’s Zoology Museum.
The researchers estimate that the Electrophorus species diverged twice.
The first time was in the Miocene, approximately 7.1 million years ago, when they separated from their common ancestor.
It was not until the Pliocene, approximately 3.6 million years ago, that Electrophorus voltaic and Electrophorus electricus reached their present status.
“Electrophorus electricus can be found an area known to geologists as the Guiana Shield, encompassing the northern regions of three Brazilian states (Amapa, Amazonas and Roraima), and Guyana, French Guiana and Suriname,” the scientists said.
“Electrophorus voltai inhabits the Brazilian Shield, which encompasses the south of Para and Amazonas, as well as Rondonia and the north of Mato Grosso.”
“Electrophorus varii inhabits the lowest part of the Amazon Basin, living in turbid rivers with relatively little oxygen and sandy or muddy bottoms.”
The team’s paper was published in the journal Nature Communications.
C. David de Santana et al. 2019. Unexpected species diversity in electric eels with a description of the strongest living bioelectricity generator. Nature Communications 10, article number: 4000; doi: 10.1038/s41467-019-11690-z