Answer:
Gills extract out oxygen from water and carbon dioxide is carried away by water. With the help of gills fish force the water, they flow past lots of tiny blood vessels. There is a seeping of oxygen through blood vessels wall and carbon dioxide is taken out. With gills water flow through their mouth over the gills and taken out with the helps of gill slits. Because water is heavier and water moves in one direction.
Step-by-step explanation: