Recirculation Aquaculture System_Part_2
Fish Metabolism Understanding How Fish Breathe In order to successfully design and operate a life support system for fish, one must have a basic understanding of the physiological requirements of fish. Fish use the oxygen dissolved in the water for respiration. This dissolved oxygen (DO) is gas in simple solution (not the covalently bound oxygen in the water molecule). Fish extract this oxygen with their gills. Water has relatively little DO (<14 mg/L) compared to the oxygen (240 mg/L) in air, so fish must be efficient in getting it. One factor that contributes to this efficiency is the unidirectional flow of water through their gills. Terrestrial animals have bidirectional flow (in and out of the same tube, the trachea) which is inefficient in that fresh inspired air mixes with stale expired air. With unidirectional flow, there is no mixing. Another factor is the countercurrent movement of blood and water. At the lamellae , blood flows one way and water the