Actually, a bowfin is a very cool fish. They are a primative species of fish that dates back to the triassic (230 million years ago; well before the first birds or mammals).
Bowfin are the only living representative of their order and are found ONLY in freshwater. They are closely related to garfishes and teleosteans. Bowfins are members of the ray-finned fishes which is the largest group of living fishes.
Bowfins are one of the few species of fish that aestivate, or spend their summers (when water temperature is high and dissolved oxygen is very low) in torpor (suspended animation - decreased body temp and greatly reduced metabolism). This is a type of hibernation. Most fish that aestivate do so buried in the mud or make mucous cocoons. For this reason, they must be able to maintain homeostasis by breathing air. During periods of regular or sustained activity they respire through their gills and absorb oxygen through the skin just like most modern fishes.
The functions of the gas bladder in fishes include hydrostatic balancing/neutral buoyancy, sound production, sound reception, and respiration. Bowfins have a specialized gas bladder that provide the latter function. If you ever catch one and keep it, look at the gas bladder. You will see that it is compartmentalized (divided by septa) and highly vascular to allow for exchange of air and the passage of oxygen into the blood stream.
