Sauron, the vegetarian piranha

More than 40 per cent of South American freshwater fish species have not yet been scientifically described. New discoveries are therefore the order of the day, but not all finds are as fascinating as Myloplus sauron, which a team led by Valéria Machado from the University Federal do Amazonas is presenting to the world: The species belongs to the piranha family, eats a purely vegetarian diet and has a vertical black line across the centre of its body, which reminded the research group of Sauron's eye - the big baddie from "Lord of the Rings".

The Sauron fish belongs to the group of pacus, which are closely related to the (unjustly feared) carnivorous piranhas, but feed on a purely vegetarian diet, such as fruit that has fallen into the water. As an adaptation to this diet, many pacus have developed teeth that resemble those of humans. Different teeth are also frequently used to distinguish individual species from one another. However, convergent evolution of the same tooth types regularly occurred in different regions because similar food sources were developed independently of each other.

With the help of DNA analyses, Machado and Co. were not only able to clearly distinguish Myloplus sauron from its close relative M. schomburgkii, but also a second species called M. aylan. It is possible that all three species are not descended from a common ancestor, but have each evolved from their own lineages - although further studies are needed to show this, according to the authors.

So far, Sauron and Co. are not yet considered endangered; initial inventories show that they are widely present in their distribution area. However, there are plans for dams, which could have a significant impact on the river ecology.

The bad reputation of piranhas is said to go back to former US President Theodore Roosevelt, who travelled through the Amazon on research trips. One of his notes contains an eyewitness account of a cow being driven into a waterhole with piranhas, which quickly devoured the animal. However, this only happens when the fish are defending their nests or are completely starved because they have been isolated from the rest of the river and its food sources.

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