Physiology of Finfish and Shellfish

2.1.19. Ventilation of gills

Gill takes oxygen nearby water and O₂ will deplete very quickly. Renewal of water is therefore very important which can be accomplished by i) moving the gill through the water or ii) by moving water over the gill. The second is the much more feasible method. The movement of water over gill is accomplished by pumplike mechanisms. Fishes have buccal and opercular pump to maintain flow. In tuna which is fast moving in nature has immobile gill cover and it require high water flow over the gill by taking water into the mantle cavity, and by ejecting the water by jet propulsion. Fast moving fishes have largest gill area than the slow movers. This help to desire more oxygen for its activity.