The fish that can survive on land and walk using its gills
The climbing perch is an extraordinary freshwater fish native to Asia that can breathe atmospheric oxygen using a specialized organ. When its water source dries up, it can crawl across dry land for days in search of a new home. It walks by flexing its body and using sharp, flared gill covers like makeshift crutches, even managing to climb up low tree trunks in wet conditions.
Breathing Air with a Labyrinth Organ
Most fish rely entirely on dissolved oxygen in water, passing a continuous stream over their delicate gill filaments to sustain cellular respiration. The climbing perch and its relatives in the climbing gourami family, Anabantidae, possess a remarkable evolutionary adaptation that frees them from this limitation: the labyrinth organ. Located in a cavity above the gill arches, this structure consists of intricate, folded plates of bone lined with highly vascularized tissue. By surfacing and gulping air directly into this chamber, oxygen diffuses into the bloodstream much like it does across the lining of a terrestrial animal's lungs.
This adaptation is not merely an emergency backup system; for many adult climbing gouramis, it is an obligate necessity. In stagnant, warm, or heavily vegetated waters where dissolved oxygen plummets to near zero, normal gills fail to provide sufficient oxygen. The labyrinth organ allows these fish to thrive in swampy ditches, shallow rice paddies, and temporary seasonal pools that would prove lethal to other aquatic species. If denied access to the surface to replenish the air in their suprabranchial cavity, these fish can actually asphyxiate and drown despite being fully submerged in water.
Mechanics of Overland Travel
When seasonal droughts cause their native watercourses to dry up, climbing perch do not simply wait for the mud to desiccate. Instead, they make deliberate journeys across dry ground in search of deeper, more permanent bodies of water. Their method of terrestrial locomotion is unique among freshwater vertebrates. Lacking genuine limbs, the fish relies on a coordinated combination of body flexions, rigid pectoral fins, and specialized, serrated gill covers known as opercula.
To travel across terrain, the fish flares its opercular plates outward. The margins of these gill covers are lined with stiff, sharp spines that catch against soil, grass stems, or gravel. By planting these flared plates into the ground like miniature crutches or anchors, the fish stabilizes its forward section and prevents backward slippage. It then pushes vigorously against the earth using its muscular tail and pectoral fins, producing a jerky, wriggling forward crawl that can propel it across hundreds of meters of open terrain under damp or humid conditions.
The Legend and Reality of Tree Climbing
The climbing perch earned its popular name and scientific classification after early European naturalists documented specimens in unexpected locations. An often-cited eighteenth-century account recorded finding a live fish wedged into the crevice of a palmyra palm several feet above the ground. While this historical report led to claims that the fish routinely scaled tall trees to drink sap or capture terrestrial insects, modern naturalists offer a more grounded explanation for such occurrences.
While climbing perch do not scale vertical tree trunks as a deliberate habit, their powerful spines and gripping opercula enable them to scramble up sloping riverbanks, negotiate fallen logs, and push through dense, low-hanging emergent vegetation. In many historical instances, fish found lodged high in trees were likely carried there by predatory birds, such as kites or storks, and subsequently dropped or stashed, rather than having climbed the height of the trunk on their own power.
A Formidable Defense Mechanism
Travelling out of water exposes fish to extreme vulnerability from terrestrial and avian predators, yet the climbing perch possesses a formidable physical defense. When threatened or seized by a predator, the fish erects its dorsal and anal fin spines while locking its opercular gill covers firmly in an outward, flared position. The stiff, barbed edges of these plates make the fish exceptionally wide and abrasive, transforming a soft meal into a rigid, spiny obstruction.
This defensive posture frequently proves fatal to would-be predators. Herons, larger fish, and aquatic reptiles that attempt to swallow a climbing perch whole often find the fish wedged tightly in their throats. Because the flared opercular spines point backward, the fish cannot be swallowed deeper or easily regurgitated. As a result, predators that misjudge the prey often choke to death, a lethal deterrent that protects the climbing perch population as a whole from casual predation during terrestrial migrations.
Survival and Ecological Impact
The extreme hardiness of the climbing gourami family extends beyond air-breathing and overland locomotion. In periods of acute drought where no alternative water can be reached, climbing perch are capable of burrowing into damp mud and entering a dormant state, surviving for extended intervals until monsoon rains refill the basin. Their tolerance for wide temperature swings, low water quality, and even mildly brackish water makes them among the most resilient freshwater organisms across their native range in Asia and Africa.
However, these same evolutionary strengths pose significant ecological concerns when climbing perch spread beyond their native ecosystems. Outside their historic habitats, their aggressive feeding habits, rapid overland dispersal, and resistance to environmental stress allow them to outcompete indigenous freshwater species. Furthermore, native predators that lack evolutionary experience with the climbing perch's locking opercular spines suffer elevated mortality rates when attempting to feed on them, disrupting local aquatic food webs.
Key takeaways
•Climbing gouramis possess a specialized suprabranchial labyrinth organ that enables them to extract oxygen directly from atmospheric air.
•Overland locomotion is achieved by flaring spine-lined gill covers (opercula) to grip the substrate while propelling the body forward with the tail and fins.
•While historical accounts claimed the fish actively scaled tall trees, their climbing is limited to low obstacles, fallen logs, and sloping banks.
•The fish erects backward-facing opercular spines when threatened, which can fatally choke predators that attempt to swallow it whole.