The labyrinth organ is a special breathing structure that lets certain fish — bettas, gouramis, paradise fish and their relatives — gulp air directly from the water surface. It works like a primitive lung, letting these fish survive in warm, oxygen-poor water where most fish would suffocate.

Here is how it works and what it means for keeping these fish.

How it works

The labyrinth organ is a maze-like structure of folded bony plates in the head, richly supplied with blood vessels. When the fish gulps air at the surface, oxygen is absorbed directly into the blood through this organ, supplementing what the gills extract from the water.

Fish with this organ are called anabantoids or “labyrinth fish”.

Which fish have it

• Bettas (Siamese fighting fish)
• Dwarf gouramis and other gouramis
• Paradise fish
• Kissing gouramis

What it means for care

• They must reach the surface — never fully seal a tank lid; leave an air gap of warm, humid air above the water.
• Occasional surface gulping is normal, not a sign of low oxygen. See fish at the top of the tank.
• They tolerate low-oxygen water better than most fish, but still need clean, cycled water.

Frequently asked questions

What is a labyrinth organ in fish?

It is a maze-like breathing structure in the head of bettas, gouramis and paradise fish that lets them absorb oxygen from air gulped at the surface, like a primitive lung.

Which fish have a labyrinth organ?

Anabantoids — bettas, gouramis (including dwarf and honey gouramis), paradise fish and kissing gouramis all have a labyrinth organ.

Why does my betta go to the surface for air?

Bettas have a labyrinth organ and naturally gulp air at the surface. Occasional trips up are normal; constant gasping signals low water oxygen and needs attention.

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— Jaqline Smalling, FishForever