Oxygen "wants to" dissolve in oxygen-depleted water, especially ionic/salty water, specifically blood.
It's much less eager to permeate from one liquid into another liquid of comparable salinity.
Sharks have an additional disadvantage over bony fishes, in that they must be moving for their gills to work at all.
The name for this is -"obligate ram ventilators" which is a fantastic phrase.
Oxygen "wants to" dissolve in oxygen-depleted water, especially ionic/salty water, specifically blood.
It's much less eager to permeate from one liquid into another liquid of comparable salinity.
Sharks have an additional disadvantage over bony fishes, in that they must be moving for their gills to work at all.