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Wildlife: Feared but Not Fearless
It turns out piranhas—the flesh-eating fish known for stripping prey to the bone in seconds—are hardly bad to the bone themselves.
New research is proving that the legendary South American fish school not to attack but rather as a defensive measure to protect them from being eaten.
“Piranhas are under constant attack from a number of large predators including river dolphins, caiman and some of the world’s largest fish, such as the piracucu,” says Anne Magurran, a scientist at the University of St. Andrews in Scotland, who is studying these fish in their natural habitat in collaboration with Helder Queiroz of the Mamiraua Sustainable Development Institute in Brazil. “Their cautious behavior is crucial to avoid being eaten.”
In fact, contrary to popular belief, piranhas are scavengers more than predators, eating mainly fish, plants and insects. The researchers also discovered that the schools have a distinct structure: The bigger, older fish tend to swim in the middle because they are reproductively mature and less willing to take risks during foraging. Younger fish are at the edge of the group, where they can get access to food sooner and grow faster.
The researchers also found that the size of the school changes depending on predation risk. “At high water the fish swim in small schools, as there is more space to avoid predators and the threat is low,” says Magurran. “However, when the water level drops, isolating the flood water into smaller lakes and channels, schools can grow to more than 50 fish due to the close proximity of predators.”
But while piranhas rarely attack live mammals in the water, with their sharp teeth these fabled fish are still nothing to wiggle your toes at.
