Piranhas weigh 7 to 8 pounds and grow up to 18 inches in length. They are found in the rivers of South America, and they have a lifespan of up to 25 years.

Piranhas have a singe row of sharp teeth, and they feed on fish, mammals, insects, aquatic plants and birds. Piranhas feed together in groups when there is a shortage of food or blood in the water. Groups of piranhas are called schools, and the groups may consist of over 1,000 fish. Piranhas have gray, yellow, blue or red scales. Their teeth may be used to make weapons and other tools. Piranhas mate during April and May, and females can lay up to 5,000 eggs.