How Do Fish Breathe?

Mammals breathe through lungs. Earthworms and amphibians breathe through their skin. Fish breathe through gills.

Unlike mammals and amphibians, fish spend their lives underwater. Lungs must be dry to work properly. Therefore, fish could not have lungs. But fish still need oxygen to survive. To get that oxygen, they use their gills. Gills are special organs that help remove the oxygen from the water so fish can breathe.

If you look at a fish, you can see its gills. They look like feather-like pieces of skin on the side of the head of a fish. Usually a fish will have four gills on each side of its head. The feather-like parts of the gills are full of blood vessels.

To use its gills, the fish takes water in through its mouth. It then pushes the water out through its gills. The oxygen from the water connects with the blood vessels. This helps push oxygen into the blood of the fish. The oxygen travels to the fish's cells.

Fish need to pump a lot of water through their gills to get enough oxygen to survive, so you will regularly see a fish opening and closing its mouth as it swims through the water.