Physiology of Finfish and Shellfish (2+1)

2.1.20. Counter Flow Mechanism

The stream of water flowing over the gill and the steam of blood running within the gill flow in opposite direction to each other and this will help for effective removal of oxygen and this called counter current flow. Just as blood is about to leave the gill lamellae, it encounter water whose oxygen has not yet removed. Thus, this blood taken up oxygen from water which is still has the full oxygen content of inhaled water, and this permits the O₂ content of blood to reach the highest possible level. As the water runs further between the lamellae, it meets blood with lower and lower oxygen content and it therefore continue to give up more oxygen. The lamellae, along its entire length; serves in taking up oxygen from water and the water may leave the gill having lost as much as 80 -90% of its initial oxygen content.