Navigating one of the tributaries of the Amazon to Iquitos about 40 miles near the town of Indiana. The most common piranhas in aquariums usually measure between 30 and 35 centimeters. It is best to buy small specimens to see them grow. They are social animals, so it is good to have five or six copies, but not many as they can have aggressive behavior. Be careful because if there are times that piranhas are hungry, they often satisfy their hunger by devouring the weaker individuals.