Labyrinth organ
A folded chamber above the gills that lets bettas, gouramis and climbing perch breathe air from the surface.
Also: air-breathing organ, suprabranchial organ
The labyrinth organ is a maze of thin, folded bony plates in a chamber above the gills, covered in skin rich in blood vessels. Fish that have it gulp air at the surface and take oxygen from it, so they can live in warm, still, low-oxygen water such as rice paddies, ponds and swamps. The Siamese fighting fish, gouramis and the climbing perch belong to this group. Snakeheads and the walking catfish, magur, have different air-breathing organs, and Asian markets have long kept these fish alive for sale in shallow water.