What does a shark use its gill for?

A shark uses its gills to breathe. Sharks are fish, and like other fish, they need to extract oxygen from the water to survive. Sharks do this by drawing water in through their mouths and expelling it through their gills. The water passes over the gill filaments, which are covered in tiny blood vessels. The oxygen in the water diffuses into the blood vessels, and the deoxygenated water is expelled through the gill slits.