Some fishes can extract 80% of the oxygen from water flowing through their gills through countercurrent exchange.

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Countercurrent exchange is a mechanism that enables some fish to extract a high percentage of oxygen from water. By having blood flow in the opposite direction to water over their gills, they maximize oxygen absorption, allowing some species to extract up to 80% of the oxygen from the water.

Some Fishes Can Extract 80% of the Oxygen from Water