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How does the labyrinth organ help gouramis and Siamese fighting fish breathe air?

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A porcupine fish in the Andaman Sea — fish *Diodon hystrix* is a species of porcupine fish. These fishes are short and broad-bodied, with large eyes and spines covering their skin. Like puffer fishes, they inflate their bodies when threatened.

The labyrinth organ is a specialized, vascularized structure located in a chamber above the gills of labyrinth fish, such as gouramis and Siamese fighting fish.12

While these fish continue to use their gills to extract oxygen from water, the labyrinth organ functions as a rudimentary lung. It allows the fish to gulp air at the surface through their mouths and absorb oxygen directly into the bloodstream via the organ's dense network of blood vessels. This evolutionary adaptation is essential for survival in warm, oxygen-poor freshwater environments where traditional gill respiration alone may be insufficient.12

It is important to note that this respiratory structure is distinct from the inner ear's labyrinth, which is a sensory system found in all vertebrates responsible for balance and hearing.3