Here's how it works:
* Gills are feathery organs located on the sides of a fish's head. They are made up of thin, delicate filaments that are rich in blood vessels.
* Water flows over the gills, passing over the filaments. This allows oxygen from the water to dissolve into the blood vessels within the filaments.
* Carbon dioxide, a waste product of respiration, is released from the blood into the water.
* The blood then carries the oxygen throughout the fish's body.
So, the gills act as a fish's "lungs," allowing them to extract oxygen from the water and release carbon dioxide.