Question

Why is the rate of breathing in aquatic organisms much faster than that seen in terrestrial organisms? How does oxygenation of blook take place in fishes?

Answer 1

the air is less dense in water. so oxygen level is much lesser.
in order to  acquire as much as oxygen as possible aquatic organisms breathe much faster than terrestrial  organisms.

i dont know about the second part sorry....

Answer 2

Aquatic animals take in the oxygen dissolved in water. The amount of dissolved oxygen in water is fairly low compared to the amount of oxygen in the air. Therefore, rate of breathing in aquatic organisms is much faster than in terrestrial organisms.