Some fish species possess remarkable adaptations allowing them to survive and even thrive on land, challenging traditional understandings of aquatic life. Certain fish have evolved specialized physiological mechanisms and behaviors that enable them to spend significant periods away from their aquatic habitats. This capacity allows them to exploit new resources and endure conditions lethal to most other fish.
Masters of Terrestrial Survival
Several fish species are known for their ability to survive out of water for varying durations. Mudskippers, for instance, are amphibious gobies that spend much of their time on land in tropical and subtropical regions. They use their muscular pectoral fins like limbs to crawl, hop, and even climb low-hanging tree branches. Their eyes protrude from their heads, providing enhanced vision above water. Mudskippers can remain out of water for days, foraging and interacting on muddy surfaces.
The walking catfish (Clarias batrachus), native to Southeast Asia, is another example, known for its ability to “walk” across dry land. This eel-like fish uses its pectoral fins and a wiggling motion for terrestrial locomotion. Walking catfish can survive out of water for up to 18 hours.
Similarly, snakehead fish, a group of freshwater fish, are partially amphibious and can endure up to four days outside water. The climbing perch can use strong spines on its pectoral fins to travel over land and may live on land for up to six days. Even the mangrove rivulus can survive for up to 66 days by hiding in moist cavities within rotten wood when their pools dry up.
How They Survive Out of Water
The ability of these fish to survive outside aquatic environments stems from specialized biological adaptations. Many air-breathing fish utilize auxiliary respiratory modes when water oxygen levels are low or when they emerge onto land. Some species, like lungfish, possess true lungs, which are modified swim bladders directly connected to their alimentary tract. These lungs feature honeycomb-like cavities lined with a dense network of blood vessels, facilitating efficient gas exchange with the air. African and South American lungfish have two such lungs, while the Australian lungfish has one.
Other fish, like the walking catfish, have evolved specialized “labyrinth organs” located above their gills, which are tree-like structures designed for air breathing. Mudskippers primarily absorb oxygen through their skin and the lining of their mouth and throat, a process known as cutaneous respiration. This method requires their skin to remain moist, which they achieve by rolling in damp mud or retaining water in their enlarged gill chambers. Many amphibious fish also secrete a protective layer of mucus over their bodies to prevent dehydration while on land.
Why Fish Leave the Water
Fish venture out of water for various reasons, often driven by environmental pressures. A primary motivation is the search for new water sources, especially during droughts when their original habitats begin to dry up or experience low oxygen levels. Walking catfish, for example, frequently “walk” to disperse to new bodies of water, particularly after heavy rainfall. Eels are also known to travel overland to reach new waterways.
Escaping predators is another reason some fish leave the water. Mudskippers can quickly hop out of the water to evade aquatic threats. Terrestrial excursions can also be driven by the search for food; mudskippers feed on invertebrates and algae found on land, while walking catfish consume terrestrial prey like earthworms. Some species, such as mudskippers, also utilize burrows on land for shelter, protection from predators, and as nesting sites for laying eggs.
Long-Term Survival and Estivation
For the longest durations of out-of-water survival, African and South American lungfish employ a strategy called estivation. Estivation is a state of dormancy characterized by reduced metabolic activity, similar to hibernation but occurring in response to prolonged heat and dryness. As their freshwater habitats dry up, these lungfish burrow deep into the mud. Once buried, they secrete mucus from their skin, which hardens to form a protective, moisture-retaining cocoon around their bodies. A small opening or tube is maintained to the surface, allowing them to breathe air using their primitive lungs.
During this period, their metabolism slows significantly, and they can survive for extended periods without food or water. African lungfish have been observed to estivate in nature for three to five years, and in laboratory settings, some have survived for up to six years. During this time, they slowly digest their own muscle tissue for sustenance. When rains return, the hardened cocoon softens, and the fish emerge, gradually resuming normal activity. South American lungfish also estivate by burrowing into mud, though some do not form a distinct mucus cocoon.