How do fish breathe under water?

You have to lift your head out of the bath to breathe. But a fish can stay under water its whole life and never come up for air. What is its secret?

Air is hidden in the water

The thing our bodies really need from air is called oxygen. Here is the surprise: there is oxygen inside the water too, in tiny amounts mixed all through it. Fish have found a way to grab it.

Gills are breathing helpers

On each side of a fish’s head are special body parts called gills. When a fish swims, it gulps water into its mouth and pushes it out past its gills.

As the water flows over the gills, they catch the oxygen from it and pass it into the fish’s blood. The leftover water flows back out into the sea. The fish breathes in and out — just with water instead of air!

Could you breathe like a fish?

No — our lungs can only take oxygen from air, not water. And a fish’s gills only work in water; in the air they dry out. Every animal has the perfect breathing tools for its own home.

Wonder fact: Some fish, like the lungfish, can gulp air at the surface when their pond dries up. They have both gills and a kind of lung!