Fish that can move across land represent a remarkable testament to evolutionary adaptation. Certain species have developed unique strategies to navigate terrestrial environments. This showcases how life adapts to diverse and challenging conditions, allowing these animals to thrive in transitional habitats.
Meet the Land-Crawling Fish
Mudskippers are well-known land-crawling fish, found in intertidal habitats like mangrove swamps, mudflats, and estuaries across Africa, Asia, and Australia. These fish possess large, independently moving eyes positioned on top of their heads, resembling periscopes. Mudskippers spend a significant portion of their lives out of water, engaging in activities such as feeding, mating, and defending territories.
Another example is the walking catfish, Clarias batrachus, native to Southeast Asia and parts of India. This species has a long, eel-like body, typically brown-gray with a white underside, and lacks scales. Walking catfish are often found in warm, stagnant waters like muddy ponds, canals, ditches, and swamps. They have been introduced to other regions, including South Florida, where they are considered an invasive species due to their mobility and indiscriminate feeding habits.
The climbing perch, Anabas testudineus, is a freshwater and brackish water fish widely distributed across the Indian subcontinent, Southeast Asia, and parts of China. This species is generally brownish or grayish, with a lighter belly, and can reach lengths of up to 45 cm. Climbing perch are highly adaptable, inhabiting a range of environments including rivers, lakes, wetlands, and even temporary pools with dense vegetation.
How Fish Move on Land
Fish that move on land utilize various physical adaptations and locomotion methods. Mudskippers primarily use their strong pectoral fins, which function like “crutches” or “arms,” to propel themselves forward across muddy terrain. These fins contain mini-joints similar to elbows and shoulders, enabling a “crutching” movement where both fins swing forward simultaneously. They also use their pelvic fins for grip and their tail for additional propulsion, sometimes even skipping or jumping.
Walking catfish employ a different method, using a wiggling, snake-like motion combined with their stiff pectoral fins for support and leverage. This allows them to slither across land, especially during wet weather, to move between bodies of water. Their elongated bodies facilitate this type of undulating movement, which, while appearing ungainly, is effective for terrestrial traversal.
Climbing perch use their spiny gill covers and tail for terrestrial locomotion. They can adopt a near-upright posture, alternately driving their spiny suboperculars (parts of the gill cover) into the ground for purchase, then vaulting their body over them using tail movements. This unique mechanism allows them to move over obstacles and even climb inclined surfaces up to 25-30 degrees.
These amphibious fish also possess specialized adaptations for breathing air. Mudskippers absorb oxygen through their moist skin and the lining of their mouth and throat, a process known as cutaneous respiration, similar to amphibians. They can also trap water within their large gill chambers, allowing them to continue gill respiration while on land. To stay hydrated, mudskippers may roll in mud or flip into puddles.
Walking catfish have evolved a suprabranchial arborescent organ, a specialized tree-like structure located above their gills, which acts as a lung-like organ for atmospheric air breathing. This enables them to survive in oxygen-deficient aquatic environments. Similarly, climbing perch possess a labyrinth organ, a highly vascularized accessory respiratory organ that allows them to extract oxygen directly from the air. This adaptation aids their survival in low-oxygen waters and during their terrestrial excursions.
Why Fish Leave the Water
Fish venture onto land primarily due to environmental pressures and the pursuit of survival. One significant driver is the need to escape unfavorable aquatic conditions. During periods of drought, ponds and other water bodies can shrink or dry up, leading to overcrowding and a depletion of dissolved oxygen. Fish capable of moving overland can then migrate to new, more suitable water sources.
Low oxygen levels, or hypoxia, in stagnant or warm waters also compel fish to seek air or move to better environments. Many air-breathing fish inhabit such oxygen-poor habitats, and their ability to breathe atmospheric air provides a distinct advantage. This adaptation allows them to survive conditions that would be lethal to most other fish.
Seeking new food sources is another motivation for terrestrial excursions. The land can offer untapped resources like insects and invertebrates that are unavailable in the aquatic environment. Some fish, like the walking catfish, have been observed feeding on terrestrial prey in moist areas. This expansion of their foraging grounds enhances their chances of survival.
Fish may also leave water to find new breeding grounds or to avoid aquatic predators. By moving over land, they can bypass barriers and access isolated areas that offer safety for their eggs or young. These terrestrial movements represent evolutionary adaptations that allow these fish to persist in dynamic and often unpredictable environments.