Certain fish species possess remarkable adaptations allowing them to move beyond aquatic environments. These unique abilities challenge the typical understanding of fish, enabling them to traverse terrestrial surfaces for various purposes. This phenomenon highlights nature’s capacity for adaptation.
Notable Land-Walking Fish
Among the most recognized land-walking fish are mudskippers, a group of about 25 species found in mudflats, swamps, and mangrove forests across Africa, Asia, and South America. These amphibious fish can spend more than half their lives out of water, engaging in activities like feeding and mating on land. They are highly adapted for terrestrial life, even being able to climb mangroves to modest heights.
Another example is the walking catfish, native to Southeast Asia. While their “walk” is more of a clumsy wiggle, they use their pectoral fins and strong bodies to propel themselves across land. These fish can cover significant distances, sometimes up to three-quarters of a mile, and survive out of water for up to 18 hours. Lungfish, an ancient family of fish, also exhibit terrestrial movement, with some species able to propel themselves along surfaces in a manner resembling early land vertebrates.
Other species with terrestrial tendencies include snakeheads, which wriggle their bodies across land, and the climbing perch, known for its ability to move between water bodies. The mangrove rivulus can also survive for extended periods out of water, even climbing mangrove roots.
How Fish Walk on Land
Fish that walk on land exhibit specific anatomical and physiological adaptations that facilitate their terrestrial movement and air breathing. Mudskippers, for instance, use their pectoral fins, which are strong, muscular appendages with flexible joints akin to elbows and shoulders. These modified fins allow them to lift their bodies and propel themselves forward in a series of skips or “crutching” motions, swinging both pectoral fins simultaneously. Their pelvic fins can act as suction cups, providing stability and grip on slippery surfaces.
For respiration, these fish employ various methods to extract oxygen from the air. Mudskippers can breathe through their moist skin and the lining of their mouth and throat, a process known as cutaneous respiration. They also gulp air and store it in specially adapted gill chambers, which stay moist to facilitate oxygen absorption. Lungfish, as their name suggests, possess lungs, enabling them to breathe air and even enter a dormant state in mud burrows during droughts. Walking catfish have accessory air-breathing organs, derived from their gills, which allow them to respire in air.
The skeletal structure of these fish also shows adaptations for terrestrial support. Studies on mudskippers reveal fascia tissue in their pectoral fins, providing internal structure and strength for movement on land. Some mudskippers also have a joint connecting the shoulder and pelvic fin, which is not seen in many other fish and suggests an adaptation to support their body weight against gravity.
Why Fish Venture Ashore
Fish venture onto land for survival advantages. One primary reason is to escape aquatic predators. Moving onto land provides a temporary refuge from threats confined to water.
Seeking new food sources is another significant driver for terrestrial excursions. Land-walking fish can exploit insects, invertebrates, and detritus found in moist terrestrial areas that are inaccessible to purely aquatic fish. This expands their foraging opportunities, particularly when aquatic food becomes scarce.
Environmental conditions, such as droughts or low oxygen levels, also compel fish to move onto land. Leaving water allows them to search for more favorable aquatic conditions or survive until water returns. This adaptation enables them to colonize new territories.
Terrestrial Habitats and Survival
Land-walking fish typically inhabit environments where water and land meet, such as mudflats, mangrove forests, swamps, and floodplains. These dynamic intertidal zones often experience fluctuating water levels and oxygen availability.
Survival on land presents challenges like desiccation and temperature regulation. To combat drying out, mudskippers keep their skin moist by rolling in mud or slurping water into their gill chambers. They also burrow into the mud to stay hydrated and regulate their body temperature. African lungfish secrete a mucus cocoon to protect themselves from desiccation during dry spells, allowing them to remain dormant for extended periods.