Many fish that live in water containing little oxygen are able to breathe air. They usually have to do this in foul water, when bacterial decay reduces oxygen levels. Some fish have a special breathing organ called a labyrinth, and they rise to the surface every few minutes to breathe air into this organ. Many catfish breathe air in a similar way — they swallow it and it passes into their gut where oxygen is absorbed through the thin lining of the gut wall.
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