Originally Posted by nomel
I believe they take in air when oxygen levels in the water get too low...I don't think you should never see them do this. Maybe someone could second this.
The anabantoids need to breathe air regardless of the water quality. They posess an organ called the labyrinth, named bcause it is a maze of passages, in which the blood vessels extract oxygen from the air the fish takes in regularly at the surface. This is why it is critical to keep the aquarium well covered so the air above the water surface is always as warm as the water, and moist.
While it is believed that this organ was a natural development to allow the fish to live in very low-oxygen waters (they are all native to swamps and very slow flowing streams thick with vegetation) it is known that the fish cannot live without breathing air. This is comparable to the adaptation in certain catfish families in South America, the Corydoras being well-known examples, where the fish must regularly breach the surface and swallow a gulp of air; blood vessels in the hind gut extract oxygen and when depleted, the fsh goes back to the surface for another gulp of air. If this is somehow prevented, the fish would literally drown, since it is an integral part of their biological makeup.
With corydoras, it is believed that more frequent trips to the surface indicate deteriorating water conditions. But regardles of the condition of the water, neither the corydoras (and similar fish lke Aspidoras, Brochis, Ottocinclus, Parottocinclus...) nor the anabantoids (bettas, gouramis, paradise fish...) will abandon the practice because it is integral to their need for oxygen.