Actually, there aren't that many catfish that can survive in the open air for a "walk" between water sources. That tends to be the provence of Snakeheads and African Lungfish. The ability to breathe atmospheric air evolved to allow the fish to survive in still water pools that had no influx of new water between rainy seasons. This gives these fish the ability to survive almost anywhere in their environment, rather than just in the large river systems that always maintain good waterflow. In the case of Clown Knife Fish's, which also breathe atmospheric air, it allows them to survive in large lake systems with poor water circulation, where they have a much greater variety of prey than in the rivers of South Asia. There is actually only one catfish, Clarias batrachus, that can actually "walk" between water sources.
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