Evolution Of Air-Breathing Fish: Selective Pressures And Amphibious Adaptations Essay.

BackgroundAir breathing evolved long before fish moved on to land. When water oxygen levels are low, many fish supplement their oxygen intake using lungs or other respiratory structures (facultative air breathers).  Anabantid fishes (eg Siamese fighters), for example, have a labyrinth organ that extracts oxygen from gulped air. But some fish are obligative air breathers such as electric eels and snakeheads, they drown if they can’t …