Which fish are obligate ram ventilators?

Ram ventilation is a simpler process in which a fish swims forward with its mouth open, taking in water that passes over the gills. The drawback to ram ventilation is that the fish has to swim continuously to be able to continue breathing.

A lot of sharks breathe this way, as do some large bony fish swimmers like tunas and billfishes.

Many fishes, including sharks like the sand tiger shark, can switch between buccal pumping and ram ventilation as the situation and their swimming speed dictates.

You might think that the need to swim continuously for ram ventilation would be quite inefficient in terms of a fish’s energy requirements, compared to sitting in one place and breathing by buccal pumping.

Research with remoras – bony fishes that can switch between the two fish breathing methods – found that maintaining the same volume of water/gill flow with buccal pumping consumed as much as 5.1 percent more energy for the fish than ram ventilation.