Piranhas are obligate air-breathing fish, meaning they must breathe air to survive. They do this by coming to the surface of the water and gulping air into their mouths. This air then passes through their gills, where oxygen is extracted and sent into their bloodstream. Piranhas can also breathe through their skin, but this method is not as efficient as breathing through their gills.
Piranhas have a unique adaptation that allows them to breathe air when they are underwater. This adaptation is a pair of spiracles, which are small holes located on the top of their heads. When a piranha comes to the surface of the water, it can open these spiracles and take in air. The spiracles then close when the piranha submerges, preventing water from entering the lungs.