Question: How do fish breath underwater?

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  1. Fish have gills instead of lungs. The fish suck/drink in water and then move their muscles & throat to get water to pass through the gills as water passes by the gills Oxygen is extracted from from the water and carbon dioxide released. To do this fish (not sharks) have a gill system that allows oxygenated blood to move in one direction and non oxygenated blood to move in the opposite direction. Australian Lungfish, which are ancient fish, have both lungs and gills.