Respiratory systems of southern bluefin tunas are adapted to their high oxygen demand. Bluefin tunas are obligate ram ventilators: they drive water into the buccal cavity through their mouth, then over the gills, while swimming. Therefore, unlike most other teleost fish, the southern bluefin tuna does not require a separate pump mechanism to pump water over the gills. Ram ventilation is said to be obligatory in southern bluefin tunas, because the buccal-opercular pump system used by other teleost fish became incapable of producing a stream of ventilation vigorous enough for their needs. All species of tuna in general have lost the opercular pump, requiring a quicker movement of oxygenated water over the gills than induced by the suction of the opercular pump. Therefore, if they stop swimming, tunas suffocate due to a lack of water flow over the gills.