Fish are typically aquatic, but some species have evolved remarkable adaptations allowing them to move on land. This challenges traditional understanding of fish biology and offers insight into evolutionary transitions between aquatic and terrestrial life.
How Fish Move on Land
Fish move on land using specialized methods, often combining fin usage and body undulations. Many use strengthened pectoral fins like limbs to push themselves forward.
Others wriggle their bodies side-to-side, effective on soft ground. Some combine fin use with body undulations for momentum. These diverse strategies highlight their unique evolutionary paths.
Meet the Land-Venturing Fish
Mudskippers, found in African, Asian, and Australian mangrove swamps, are well-known land-venturing fish. They use powerful pectoral fins like legs to “crutch” across mud and climb roots. Their strong tail aids skipping and jumping, and their eyes are positioned atop their heads for wide vision.
The climbing perch, from Asia and Africa, also walks on land. It uses spiny gill covers to grip and pectoral fins with body undulations to propel itself. This allows them to travel hundreds of meters to new water sources.
Walking catfish, from Southeast Asia and Florida, move across land using stiff pectoral fins and a strong, wriggling body motion. Their spiny fins provide leverage, and their powerful tail propels them, especially at night or in wet conditions.
Lungfish, particularly African and South American species, survive dry periods by burrowing into mud and forming a cocoon. Some can use their fleshy, limb-like fins to “walk” short distances on land or along shallow water bottoms.
Reasons for Land Excursions
Fish undertake land excursions for survival and resource acquisition. They often escape deteriorating aquatic conditions like oxygen depletion or overcrowding, especially during dry seasons or droughts, by seeking more favorable environments.
They also search for new food sources, as terrestrial environments near water can offer abundant insects or crustaceans. These excursions are purposeful, aiming for new water bodies or temporary food. Avoiding aquatic predators can also prompt short terrestrial escapes.
Survival Outside Water
Fish have remarkable physiological adaptations for surviving outside water. Respiration is a primary concern, as gills collapse in air. Land-venturing fish evolved solutions like modified gills or specialized air-breathing organs. Mudskippers, for instance, absorb oxygen through their moist skin and mouth lining.
To prevent drying out, many fish secrete protective mucus, which retains moisture. Some, like lungfish, aestivate by burrowing into mud and forming a mucus-lined cocoon to survive prolonged dry periods. These adaptations are crucial for their temporary survival outside water.