a bright orange tropical fish opens and closes its mouth while water flows visibly through its body. The red feathery structures on both sides of its head move rhythmically as water passes over them. Tiny bubbles and water currents show the continuous flow entering the mouth and exiting through the side openings. A smaller fish swims nearby demonstrating the same breathing pattern with its own side organs. Coral polyps and sea plants sway gently in the background water currents. the respiratory organs of aquatic animals that extract oxygen from water