Fish need oxygen to breathe underwater too. They rely on their ‘gills’ to help them out in their breathing. Fish rely on oxygen present in the water surrounding them. That is why they need to have a system that helps them extract the small amounts of oxygen out of the water and into their bloodstream. Fish take in water through their mouths and pump it through the gills. Their gills are feathery organs that contain thousands of tiny capillaries. The dissolved oxygen moves into the blood and from there to the fish’s cells.
Why do fish have gills?
