Ram Ventilation

Some fish do not use pumping action for gill ventilation. It has been known for long that large tunas cannot be kept alive in captivity unless they are put in circular tanks where they can swim continuously. The fish swim with their mouths partly open and there are no visible breathing movements. Water flows continuously over their gills. This is known as ram ventilation.

It is now known that many fish breathe by pumping at low speed and change to ram ventilation at high speed. In this case the work of breathing is transferred from the muscles of the opercular pump to the muscles of the body and tail. However, ram ventilation is more economical as far as energy consumption is concerned than opercular pumps at high rates required for fast swimming.