Bowfin
Their physiology is quite interesting. Like gars, bowfin are bimodal breathers: they can to breathe both water and air. Their gills exchange gases in the water, and they also have a gas bladder. The gas bladder is the secret: it keeps buoyancy, and lets the fish  breathe air by a small pneumatic duct which goes from the foregut to the gas bladder. They  break the surface to gulp air. This lets them survive conditions of hypoxia which would be lethal to most species.