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Thousands of fish species — about 2,500 of them named – call the Amazon River home, but scientists estimate that nearly half of the sea creatures that lurk in this enormous expanse of water remain undiscovered.
By studying piranhas and pacus in an effort to better assess the vital biodiversity of fish in the 4,000 miles long (6,400 kilometers long) Rio, an international team of researchers found and identified a new species of pacu, a relative of the piranha with a plant-based diet and human-like teeth.
In addition to its strange pearly whites, the newly discovered species has striking orange and black markings – including a bold vertical black bar running down its flank – that researchers say resemble the fiery eye symbol of the villain Sauron from “The Lord of the Rings”, by JRR Tolkien. series of books and films. The marks inspired the name of the fish, Myloplus sauron, according to a study published Monday in the journal Neotropical Ichthyology.
“The co-authors and I thought (the name) would be a good idea – it really looks like the eye of Sauron,” said study co-author Victória Pereira, a biology graduate student at Universidade Paulista in São Paulo, Brazil. The researchers hope the pop culture reference will draw attention to the fish and efforts to protect biodiversity in the Amazon, Pereira added.
The attractive fish isn’t the only animal named after Tolkien’s Dark Lord. A genus of butterflies it was found in May 2023 with spots that looked like eyes on its wings, reminding researchers of the well-known symbol from the trilogy. There is also a kind of tree froga dung beetle and a dinosaur genus named after the character.
The confusion surrounding pacus
In addition to Myloplus sauron, the researchers also discovered the species Myloplus aylan, which they described as having a slightly thicker black bar on its flank. The genus Myloplus falls into the Serrasalmidae family of fish, made up of the piranha and pacu species.
Because piranhas and pacu are closely related and have similar characteristics, differentiating the species can be difficult, the authors noted in the study. Both pacu and piranha species can change appearance throughout various stages of their lives, and males and females often have different appearances, making it difficult to distinguish the different species, according to London Natural History Museum.
Myloplus sauron and Myloplus aylan have flat, blunt teeth used for chewing plants, a sharp contrast to the sharp teeth found in piranhas but similar to those of other pacu. Although some species of piranha are known for their carnivorous diets, all species of pacus are mainly herbivores.
Previously, these two new species were grouped with another fish, Myloplus schomburgkii, due to the shared design of the black mark on the fish’s round body. However, through closer inspection and DNA analysis, researchers discovered that three different species shared the eye-catching design.
Researchers hope to further study Myloplus sauron and Myloplus aylan to learn more about their evolution and relationships with other species, Pereira said.
“People who study the pacus recognized some time ago that there were multiple species ‘hiding in plain sight,’” said Matthew Kolmann, an assistant professor in the biology department at the University of Louisville in Kentucky who has studied the fish. He was not involved with the new study.
“The size of the Amazon and other basins, and their inaccessibility, make it a place of constant discovery,” Kolmann said in an email. “What this means is that the efforts of generations of scientists have been necessary and will continue to be necessary to increase our knowledge of the area.”
Impact of Pacus on its ecosystem
Pacus are important to their ecosystem largely due to their role in spreading seeds through their diet of mostly fruit, which makes them vital for the growth of rainforest trees and other plants. Fish tend to spread seeds far from parent plants, helping to expand the forest and limit diseases that easily spread through crowded trees, Kolmann said.
By discovering and identifying species that live in certain ecosystems, researchers will be able to better lead conservation efforts to protect threatened or at-risk animals, Kolmann said. It is particularly important for areas like the Amazon, which are under threat from habitat destruction, he added.
“We run the very real risk of losing thousands, if not hundreds of thousands, of species before we even know they exist and, by proxy, of never understanding how these species contribute to a healthy functional ecosystem,” Kolmann said. “Inventorying which species are found, where and when, is the first step in any future conservation effort.”
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