Fish survive in water primarily by using gills to extract oxygen from the water, rather than breathing air with lungs like mammals.
Here's a more detailed explanation:
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Gills: Fish possess specialized organs called gills that enable them to breathe underwater. Gills are typically located on either side of the head.
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Water Intake: A fish takes water into its mouth.
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Gill Structure and Function: The water then passes over the gills, which are composed of feathery filaments rich in blood vessels. These filaments maximize the surface area for gas exchange.
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Oxygen Absorption: The gill filaments absorb dissolved oxygen from the water. This oxygen then enters the bloodstream.
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Carbon Dioxide Removal: Simultaneously, carbon dioxide, a waste product of respiration, is transferred from the blood into the water and expelled.
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Water Expulsion: Finally, the water exits the fish through openings, usually located behind the gills.
In summary, the gills act as an interface, allowing fish to extract the oxygen they need directly from the water surrounding them. This is fundamentally different from how land animals breathe.
