Respiratory adjustments during exercise - oxygen consumption
 

During exercise, oxygen demand and uptake increases with increasing swimming speeds (see figure). In the rainbow trout, a close relative of salmon, the oxygen uptake may increase up to eight times as swimming speeds increase. The oxygen is extracted from the water and then transported by the blood to the active muscles.

If the amount of extracted oxygen per litre of water pumped over the gills is constant, then  the amount of water pumped over the gills must increase eight times as well. The amount of extracted oxygen varies between species: in some the extraction actually goes up at higher swim speeds, while in other species extraction goes down .

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