Around 450 species of fish across 49 families can breathe air, and most of them live in tropical freshwater environments where oxygen levels in the water drop dangerously low. These fish have evolved a surprising variety of ways to pull oxygen from the atmosphere: some have primitive lungs, others use modified swim bladders, and a few absorb oxygen directly through their skin. Here’s a closer look at the major groups and how they do it.
Why Some Fish Evolved to Breathe Air
Warm, stagnant tropical waters are the common thread. Swamps, floodplains, and shallow pools can see dissolved oxygen plunge below 5% of normal levels, especially at night when plants stop producing oxygen and temperatures climb. Fish trapped in these environments face a choice: suffocate or find another source of oxygen. Over millions of years, dozens of lineages independently evolved structures that let them gulp air at the surface and extract oxygen from it.
Not all air-breathing fish use this ability the same way. Obligate air breathers depend on atmospheric oxygen so completely that they will drown if held underwater, even when the water is fully oxygenated. Facultative air breathers treat it as a backup system, switching to air only when the water can’t supply enough oxygen for their needs.
Lungfish: The Closest Thing to a Fish With Lungs
Lungfish are the most dramatic example. Found in Africa, South America, and Australia, these ancient fish possess actual lung tissue connected to their throat, making them the closest living fish relatives of land-dwelling vertebrates. Their lungs are internally divided by folds of tissue that increase surface area for absorbing oxygen, similar in principle to the tiny air sacs in human lungs.
African lungfish (the genus Protopterus) and the South American lungfish are obligate air breathers. They must surface regularly or they die. African lungfish take this a step further: during droughts, they burrow into mud, secrete a mucus cocoon around themselves, and breathe air through a small opening while their pond dries up completely. They can survive in this dormant state for months. The Australian lungfish is more of a facultative breather, relying mainly on its gills in well-oxygenated water and using its single lung as a supplement when conditions worsen.
Labyrinth Fish: Bettas, Gouramis, and Climbing Perch
If you’ve ever kept a betta fish, you’ve owned an air breather. Bettas belong to a group of roughly 137 species called anabantoids, all of which have a specialized structure called the labyrinth organ. This organ sits in a chamber just above the gills and consists of folded bony plates covered in thin, blood-vessel-rich tissue. When the fish gulps air at the surface, it passes over these plates and oxygen diffuses into the bloodstream.
Gouramis, paradise fish, and climbing perch all belong to this group. They’re found across Africa and southern Asia, typically in slow-moving or stagnant water. In home aquariums, labyrinth fish need access to the surface to gulp air. A tank filled too high or covered too tightly can prevent this. While they also breathe through their gills, the labyrinth organ is essential for their survival in oxygen-poor conditions.
Snakeheads: Days Out of Water
Snakeheads are obligate air breathers native to Asia and Africa, and they’re among the most extreme land survivors in the fish world. The northern snakehead can survive out of water for up to four days, provided its skin stays moist. It uses a pair of suprabranchial chambers (similar in concept to the labyrinth organ) that allow it to extract oxygen from gulped air.
Snakeheads can also wriggle across land to reach new bodies of water, which is partly why the northern snakehead has become a notorious invasive species in parts of North America. Their combination of air breathing, land locomotion, and aggressive predatory behavior makes them nearly impossible to contain once established in a new waterway.
Walking Catfish: Overland Travelers
The walking catfish is another obligate air breather that regularly leaves the water. Native to Southeast Asia and now invasive in Florida, it uses its pectoral fins and a side-to-side body motion to push itself across land. Research shows it can still move forward even without functional pectoral fins, though the fins significantly improve speed and control.
Walking catfish breathe air using a modified gill chamber that functions much like the labyrinth organ, absorbing atmospheric oxygen from air held above the gills. They typically travel overland at night or during rain, moving between ponds, drainage ditches, and flooded areas.
Mudskippers: Fish That Live on Land
Mudskippers are arguably the most terrestrial of all living fish. Found on tidal mudflats across the Indo-Pacific, they spend the majority of their active time out of water, hunting insects, defending territory, and even climbing mangrove roots. Unlike most air-breathing fish that rely on a modified internal organ, mudskippers absorb a significant portion of their oxygen directly through their skin.
Their skin is packed with blood capillaries positioned unusually close to the outer surface, creating an efficient membrane for gas exchange with the air. The more terrestrial species, like Periophthalmus waltoni, have capillaries distributed even closer to the skin surface than their more aquatic relatives. Mudskippers also retain water in enlarged gill chambers, keeping the gill tissue moist while on land. They must stay damp to breathe this way, which is why you’ll see them periodically rolling in wet mud or returning briefly to puddles.
Gar and Bowfin: Ancient Survivors
Gar and bowfin are North American fish that use a vascularized swim bladder as a breathing organ. In most fish, the swim bladder is just a buoyancy device, but in these species it’s lined with blood vessels and connected to the throat, functioning as a crude lung. The bowfin’s circulatory system is actually modified so that blood returning from its gills can be selectively routed to the swim bladder for additional oxygen pickup.
Both are facultative air breathers. Spotted gar and longnose gar surface periodically to gulp air, especially in warm, oxygen-depleted water. Bowfin do the same, and both species are commonly found in swamps, backwaters, and sluggish rivers across the eastern United States and into Central America. Their ability to tolerate poor water quality is one reason these “living fossils” have survived largely unchanged for over 100 million years.
Other Notable Air Breathers
The arapaima of the Amazon basin is one of the largest freshwater fish in the world, reaching over two meters long, and it’s an obligate air breather. It must surface every 10 to 20 minutes to gulp air, which makes it vulnerable to hunters who wait for the telltale surface break.
The electric eel, despite its name, is not a true eel but a knifefish, and it’s also an obligate air breather. It gets roughly 80% of its oxygen from gulping air at the surface, relying on highly vascularized tissue in its mouth. The Asian swamp eel is yet another obligate species, breathing through modified chambers in its head and capable of surviving in waterlogged burrows during dry spells.
Even some common aquarium fish you might not suspect are air breathers. Several species of catfish in the family Pangasiidae, including the iridescent shark catfish popular in the pet trade, are facultative air breathers that will gulp at the surface when water oxygen dips. The Indian featherback, a popular food fish in Southeast Asia, does the same.