For Long Answer:
The rate of breathing differs between aquatic and terrestrial organisms mainly due to the difference in the availability of oxygen in water and air, as well as the mechanisms each group uses to obtain oxygen.
Aquatic organisms, such as fish, live in water where oxygen is present in a dissolved form. However, the concentration of dissolved oxygen in water is much lower than the oxygen present in the air. On average, air contains about 21% oxygen, whereas water contains only around 1% dissolved oxygen. Because of this low availability, aquatic organisms need to breathe faster to take in enough oxygen to meet their body’s energy requirements.
Terrestrial organisms like humans, birds, and most land animals live on land, where oxygen is easily available in the air. They use lungs or other air-breathing parts like tracheae (in insects) to take in air. Lungs are very efficient and do not need as much energy to work. Since air has more oxygen than water and is lighter, land animals can breathe slowly and still get enough oxygen. Also, water is heavier and thicker than air, so moving it in and out of the body takes more energy. That’s another reason aquatic animals breathe faster. In warm water, there is even less oxygen, so aquatic animals may breathe even more rapidly.
