Piranhas actually scaredycats, boffins claim

Visitors to the Royal Society's Summer Science Exhibition will be greeted with the rather disagreeable news that the feared piranha - legendary for hanging around in ferocious packs dedicated to reducing their prey to skeletal remains in seconds - actually congregate for fear of themselves ending up on the menu.

That's according to researchers from the University of St Andrews, the Mamirauá Institute in Amazonas, and the Zoological Society of London, who are probing the behaviour of the "often misunderstood" piscine deathmonger.

The exhibition blurb explains: "Fish usually form schools to gain protection from predators. However, rather than schooling for its 'safety in numbers' advantages, it was thought that red-bellied piranhas congregate in cooperative hunting groups."

Not so, says University of St Andrews professor Anne Magurran: "Piranhas have a fierce reputation, but through our research we are finding many of their behavioural choices are driven by their fear of being eaten. Piranhas face a number of predators and are influenced by the availability of food and cover.

"One interesting aspect of our research in Amazonia's flooded forests has been the seasonal differences in the piranhas' behaviour. During high water levels piranha can find food and protection easily. During the low water season, they are more at risk of attacks from predators such as dolphins and caiman.

"We are showing that piranha schooling behaviour is tuned to the seasonal cycle of predation risk and food availability. We are also examining the changes in an individual piranha's behaviour throughout its life-cycle, and the way in which these choices influence its chances of breeding and passing genes onto the next generation. Our investigation is giving us new insights into animal decision making in the wild."

This is sad news indeed for those of us who like our piranha completely misunderstood and stripping the flesh from their victims in a foaming water feeding frenzy. Now all we have to do to plunge with impunity into the Amazon is slip on a hungry-looking Flipper mask and the poor blighters will be swimming for their lives. ®

Bootnote

The Royal Society Summer Science Exhibition runs until Thursday. Location and opening hours here.