Scientists in the UK have announced that the piranhafish"s reputation21a fearsome22may well not be deserved. The fish, which is found in the Amazon in Brazil, have been23as deadly carnivores( 食肉动物 ) that work in shoals to overwhelm their prey and strip it of its flesh in seconds.
However, experts24St Andrews University say that piranhas are omnivores(杂食动物) that mainly eat fish, plants and insects. They form. big groups not to hunt but to defend25against other predators, according to the team.
"Previously it was thought piranhas shoaled as it26them to form. a cooperative hunting group," said Professor Anne Magurran. "27, we have found that it is primarily a defensive behavior. "
Piranhas can be attacked by animals28dolphins, caimans and large fish, so forming a shoal is a good way of29being killed. Piranhas of30age stay in the middle of the group for31and the32of the shoal differs according to the level of33When the water level is34, the fish form. small groups as there is space to escape, but when the water level drops, they form. large groups as protection35predators.