Piranhas are carnivorous fish that feed on dead or dying animals and some species also eat fruits and nuts during high water seasons. While they have a reputation for being ferocious, piranhas are not actually vicious and can be kept with other fish if given a lot of space and extreme care and attention. Piranhas have reddish bellies and razor sharp teeth that can grow up to 33 cm in length and 3.5 kg in weight.