How can fish breathe underwater?

 

Fish are able to breathe underwater because they have special organs called gills. Gills are bars of tissue at the side of the fish’s head. They carry masses of finger-like projections that contain tiny blood vessels. Water enters the fish’s mouth and flows over the gills. The gill filaments take in dissolved oxygen from the water and pass it into the fish’s blood. In this way the gills have the same function as the lungs of air-breathing animals.

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