Arapaima are some of the largest living freshwater fish. These giants of the amazon river basin have squishy faces and fancy tails that appear red or orange in color. Also known as 'pirarucu' and 'paiche', arapaima can survive in extremely oxygen deficient water systems because they can breathe air. In fact, their lungs are so tiny they are required to breathe air in order to survive! When an arapaima comes to the surface to breathe, it lets out a loud gulping sound that's been described as something like a cough.