Siamese fighting fish (Betta splendens) are some of the world’s most popular aquarium pets. Their shape and long fins are easily recognized by many people. What most people don’t know is that they breathe air just like you and I. Betta fish are members of the family Osphronemidae. All of these fish are have to breathe air or else they will drown. These fish, which also include the popular gourami, breathe air with the use of their labyrinth organ (this has gained them the nickname labyrinth fishes). Today I will give you a little more insight into how this organ works and why it is so important that betta fish and gourami have access to the air.
There are over 370 species of fish that have the ability to breathe air. These fish fall into two categories: facultative and obligate. Facultative air breathers only use their ability when the oxygen in the water runs low. Obligate air breathers have to breathe air because their gills can’t take enough oxygen from the water. Betta and gourami fall into this category.
As I said earlier, gourami and betta take oxygen from the air with the use of their labyrinth organ. This organ is an extension of the gill plates (bone that anchors the gills) and is made of many folds of bone. Very small blood vessels run over these folds and take the oxygen from the air in a very similar manner to lungs. Below you see a drawing of a giant gourami’s (Osphronemus goramy) gills and the labyrinth organ.
When the fish gulps air it fills this chamber. When you see a bubble rise out of your betta’s mouth it is not burping but releasing the air from the labyrinth chamber. This strange organ also allows bettas to build bubble nests and certain species of Betta spp to be mouth-brooders. This means they carry their eggs in their mouth until they hatch instead of guarding a nest.
The strange little labyrinth organ makes bettas and gourami unique among fishes we commonly see in pet stores and in our tanks. But their ability to breathe air should never be used as an excuse to keep them in sub-standard conditions. They should be appreciated for their uniqueness and treated like any other tropical fish: with clean, warm water.
Because betta fish and gourami are obligate air breathers they have to take gulps of air even at night. For a fish with no large plants or decorations near the surface this often means sleeping on the substrate and dashing to the surface for air. To prevent the fish having to exert a lot of energy to make it to the surface, offer large floating plants like water sprite or have large-leafed plants like java fern close enough to the surface. The betta hammock is an artificial leaf if you don’t want to work with live plants. Don’t put it directly under the light as bettas enjoy sleeping in the shade.