Aquatic creatures breathe at a faster rate than terrestrial organisms because the concentration of dissolved oxygen in water is much lower than the concentration of oxygen in the air, therefore they must breathe more to receive enough oxygen.
The oxygen concentration in water is 21% lower than the oxygen concentration in air.
Aquatic creatures breathe faster than terrestrial species as a result of this.
Although the amount of dissolved oxygen in the water is relatively modest compared to the amount of oxygen in the air, aquatic organisms breathe at a considerably faster rate than terrestrial organisms. Fish take in water through their mouths and propel it through their gills, where blood absorbs the dissolved oxygen.