For some Sharks, Swimming and breathing are inseparable. Of course like any other animal or living being, breathing is a must, but some sharks like Oceanic Whitetip or the Gray Reef Shark must keep swimming or sink and drown tot he bottom. They adopt a system known as 'obligate ram ventilation' in which oxygen-rich seawater passes freely through the open mouth and pharynx, over the gills and out through the gill slits as they swim forwards.

This is not true for all the species however. Many species such as Whitetip reef shark, nurse shark, and bottom dwellers like angel shark and wobbegongs are able to rest at sea floor and extract the oxygen from the water through their gills. Whitetip reef sharks open their mouths, expand the walls of the pharynx, and cause the water to rush in. By closing the mouth and raising the floor, the water is propelled over the gills and out through the gill slits.

All the sharks breathe through gills. Most modern sharks have 5 gills but some primitive one have six to seven gills too.