How Fish Breathe Underwater

You breathe air with your lungs. Fish breathe water with their GILLS! Here is how it works: a fish gulps water through its mouth. The water flows over the gills, which are slits on the sides of the fish's head. The gills grab oxygen from the water (yes, there is oxygen dissolved in water!) and send carbon dioxide back out. Then the water flows out through the gill openings. Fish are constantly gulping water — it is like they are breathing nonstop!