Fish extract oxygen from water through a process called gill respiration. Gills, which are specialized respiratory organs, allow fish to absorb dissolved oxygen as water flows over them. The oxygen diffuses from the water into the fish's bloodstream while carbon dioxide diffuses out of the blood into the water. This efficient system enables fish to thrive in aquatic environments where oxygen levels can vary. Understanding gill respiration is crucial for studies related to aquatic biology and the impact of environmental changes on fish populations.