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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