New species of vegetarian piranha named after Lord of the Rings villain Sauron

A new species of vegetarian ‘piranha’has got its eye on you.

With a round body and a large black band down its side, Myloplus sauron has been named in honour of J.R.R. Tolkien’s most well-known villain. Unlike its Lord of the Rings namesake, however, this fish is much less bloodthirsty, with a diet consisting mostly of plants.

It’s one of two new species recently named by scientists as part of an effort to see through the confusion surrounding piranhas and their relatives, and better understand the fish living in and around the Amazon River.

Dr Rupert Collins, the Natural History Museum’s Senior Curator of Fishes, is one of the scientists who helped to describe the species.

“As soon as one of my colleagues came up with the name for this fish, we knew it was perfect for it,” Rupert says. “Its pattern looks a lot like the Eye of Sauron, especially with the orange patches on its body.”

“With so much undescribed biodiversity in the Amazon and surrounding rivers, its name is also a good reminder to keep an eye out for undescribed species in South America.”

Following its description, Myloplus sauron joins a select club of animals named after the literary villain, including a dinosaur, a frog, and a group of butterflies.

The study was published in the journal Neotropical Ichthyology.

Piranhas – South America’s misunderstood fish

Piranhas are no strangers to villainy, having appeared in countless books and films as agents of evil. The James Bond villain Blofeld fed an unfortunate employee to them in You Only Live Twice, while highly fictionalised versions of the fish headline the Piranha film franchise.

However, in reality, piranhas don’t really deserve their reputation as bloodthirsty fish. While they are known to bite, their reputation of reducing an animal to its bones in a matter of seconds isn’t quite true.

“The former US President Teddy Roosevelt is responsible for much of the piranhas’ reputation,” Rupert says. “He wrote about a cow being torn apart in front of him during a visit to South America, cementing their ferocious image in the public consciousness.”

“What actually happened was that the piranhas had been rounded up in nets and starved, driving them into a feeding frenzy when the cow was pushed into the water. Generally, the fish will only attack like this when they are very hungry or defending their nests.”

In fact, many species commonly called piranhas aren’t meat-eaters at all. While they might look like piranhas, the closely related pacu fish lack the sharp teeth needed to eat meat and instead consume plants and fruits.

With more than 100 species in Serrasalmidae, the family containing piranhas and pacus, telling apart and understanding how they are related is tough even for an expert. Their genetics can be complicated to unravel, while many of their external characteristics appear to be similar due to the process of convergent evolution.

“Many species were established using differences in teeth, but similar teeth have popped up repeatedly in distantly related fish,” Rupert explains. “They can also look very different at every stage of their life, with one species containing animals with many appearances.”

Until recently there was at least one species that researchers could confidently identify. With a bold black band down its side, Myloplus schomburgkii could easily be picked out in rivers across South America.

But recent research suggested that this fish might not be all it seemed, and now this new study has revealed that it’s not one species, but three.

The pacu problem

Splitting the species wasn’t that straightforward though. When the study’s authors went back to investigate M. schomburgkii, they were faced with a major issue – they couldn’t find the holotype. This is the specimen used to define a species, and is needed to compared to newer specimens to identify what exactly they might be.

However, when the fish was described in 1841 descriptions of a new species were not as detailed as they are now. So despite efforts to locate the holotype, all the researchers could find was an illustration of it.

The next step was collecting new specimens from across South America and comparing their DNA. They found that there appeared to be three distinct genetic groups, with close examination of the fishes’ bodies revealing subtle differences in their colouration, body proportions and number of scales.

Eventually, the researchers gathered sufficient evidence to prove that there were two new species, M. sauron and M. aylan, in addition to the redescribed M. schomburgkii. But the genetic data also raised more mysteries surrounding these pacus.

“We found a population in the Tapajós river where these fish had a big spot rather than a black band,” Rupert says. “While this might mean they are different species, the DNA evidence was borderline, suggesting they might just be a distinctive population.”

“More widely, there also wasn’t enough evidence to suggest whether these three species all descend from one common ancestor, or whether they evolved convergently. For now, we’ve left them in the Myloplus genus, but they might be moved in the future.”

The future for these species seems good, at least for now. While the construction of hydroelectric dams in the region has raised concerns about the impacts on rivers, the widespread distribution of these fishes means that they should be able to survive in the short term.

Other South American fishes, however, might not be so lucky. With as many as 42% unknown to science, identifying the continent’s fish species and where they are found will help scientists to understand the threats facing them and help these animals survive.