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Let's trace how a bony fish like the Rohu breathes: 1. Water Intake: The fish opens its mouth to take in a gulp of water. 2. Path: Water flows from the mouth into the throat cavity. 3. Gas Exchange: The water is forced over the four pairs of gills. Inside the gills, blood vessels pick up oxygen and release carbon dioxide. 4. Protection: During this process, the Operculum (gill cover) stays closed. 5. Exit: Once the oxygen is taken, the fish opens its Operculum. The water rushes out through this opening, cleaning the gills as it leaves.