Physiology of Finfish and Shellfish (2+1)

2.1.10. Classifications of respiration

By species

• Aquatic respiration
• Buccal pumping

Aquatic respiration is the process whereby an aquatic animal obtains oxygen from water .

Buccal pumping is a method of respiration in which the animal moves the floor of the mouth in a rhythmic manner that is externally apparent.

Earth's natural bodies of water have a low oxygen concentration—much lower than the level of oxygen in air at the Earth's surface. Smaller organisms can obtain sufficient oxygen through the skin (e.g. flatworms ), but larger organisms require special structures to collect enough oxygen to sustain life. This oxygen comes from molecules of oxygen gas (O₂) dissolved in the water. The oxygen atom present in the water molecule (H₂O) is not suitable for respiration.

Aquatic animals have evolved gills and in order to supply the animal with sufficient oxygen to survive, these organs must be much more efficient than our lungs. Marine invertebrates such as crustaceans, mollusks and echinoderms have gills, and although they vary structurally somewhat from teleosts, the basic process is the same.