How do fish breathe underwater?

Fish breathe because water goes into their mouths. It washes over soft cheek flaps. The flaps grab tiny air bits. Then fish swim on.

Fish breathe by pulling water into their mouths and pushing it out through gills, the feathery parts on the sides of their heads. Gills take oxygen from the water, so the fish can live. It is a little like using a straw, but instead of sipping juice, the fish is sipping water for air.

Fish breathe with gills, which are thin, feathery parts on the sides of the head. A fish takes water into its mouth and pushes it over the gills. The gills pull out oxygen, the gas animals need to live, and the fish’s blood carries it through the body. Then the water flows back out. Fun fact: some fish, like lungfish, can also breathe air when their water dries up.