In the second film, a bunch of piranhas attempted to attack Scrat after he fell into the water. Scrat defeated all of them with his "Squirrel Fu", or "Nut Fu". Despite the fact they prefer tropical climates, they live just below the ice.
In the third film, they are seen when one of the Baby Dinos, Egbert puts his head underwater. The piranhas show their teeth, and then Egbert shows his teeth, scaring them away. Unlike real piranhas, they fear the dinosaurs even in large groups of healthy fish. But this mau have been because Egbert's teeth