Piranhas form swarms to protect themselves from enemies and not to hunt together. Photo:
Reading Piranhas do not make swarms to hunt other animals, but to protect themselves from enemies. Accordingly, in the swarms the larger, more experienced fish swim in the middle. That excludes Anne Magurran from the University of St. Andrews in Scotland and Helder Queiroz from the Mamirauá Institute in Brazil observing the animals in their natural habitat in the Amazon. Contrary to popular belief, piranhas are not aggressive predators, but omnivores, feeding mainly on carrion, insects and plants. Threatened by many large predators such as river dolphins, caimans and piracucu fish up to three meters in length, the piranhas form different sized swarms. The size of the swarm depends on the total risk to which the fish are exposed. This risk is determined by the type of robber and the available space. At high tide the piranhas make small flocks, as they have more space to avoid predators. At a low water level, however, the swarms are larger. Depending on rainfall and meltwater from the Andes, the water level changes by up to twelve meters during one year.

Although there is an ever-present particular structure within a swarm, a swarm does not always consist of the same fish. Also, there is no "leader" or cooperation within the swarm. The individual piranhas pay more attention to themselves than to other conspecifics. Mature, mature fish swim in the middle of the swarm, where they are best protected. Younger, smaller fish, on the other hand, stick to the outside, from where they usually get more quickly to food and therefore can eat more of it, which in turn grow faster.

The Piranhas are a total of five South American fish genera with 39 previously known species. They are between 15 and 40 centimeters in size, their body is flattened on the side and they have very sharp teeth, with which they can easily remove pieces of meat from their food. Piranhas are to be found in almost all rivers of South America and their catchment areas.

Communication from the British Royal Society, London ddp / science.de? Tobias Becker advertisement

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