While most fish are aquatic, some species have evolved remarkable adaptations to survive and even thrive outside of water. These unique abilities challenge common perceptions of fish, showcasing life’s incredible diversity and adaptability. Their existence highlights a fascinating intersection between aquatic and terrestrial survival.
Fish That Can Survive Out of Water
Several fish species demonstrate an astonishing capacity to endure and navigate terrestrial environments. Mudskippers, found in mangrove swamps, are highly amphibious, spending significant time out of water. They breathe through their skin and mouth lining, remaining on land for days, sometimes up to 3.5 days, if their skin stays moist. They use strong pectoral fins to “walk” or “skip” across muddy surfaces.
Lungfish are known for surviving extreme droughts. African lungfish burrow into mud when habitats dry, secreting a mucus cocoon. They enter estivation, a dormant state that slows metabolism, allowing them to survive for months or even years without water.
The walking catfish, native to Southeast Asia, is known for traversing dry land. This fish “wiggles” across surfaces using pectoral fins for support and snakelike body movements. They can survive out of water for approximately 18 hours, moving to find new aquatic environments.
Eels, such as American and European eels, can undertake short overland journeys. Their muscular, serpentine bodies allow them to slither across moist ground, bypassing obstacles or accessing new water bodies.
Snakehead fish, found in Africa and Asia, are robust predators capable of terrestrial movement. They propel themselves by wriggling their bodies and using their fins, surviving on land for up to four days if conditions are moist. These fish are often considered invasive in non-native regions due to their hardiness and ability to spread overland. The climbing perch, an Asian freshwater fish, similarly travels across land using its pectoral fins and tail. It can survive several days out of water in moist conditions and has been observed burying itself in mud during dry periods.
Breathing and Movement Adaptations
These fish employ diverse mechanisms to survive outside their aquatic homes. Respiration on land often involves specialized air-breathing organs. Lungfish, for instance, possess primitive lung-like structures developed from their swim bladders, enabling them to gulp air directly from the surface. Other species, like climbing perch and snakeheads, utilize labyrinth organs or similar suprabranchial organs, which are highly vascularized structures near their gills that extract oxygen from the air.
Many amphibious fish also rely on cutaneous respiration, absorbing oxygen directly through their skin. This method is prominent in mudskippers and eels, where a thick mucus layer keeps their skin moist, facilitating gas exchange. Some, like electric eels, have vascularized mouths that function as primary sites for gas exchange when air-breathing. These varied respiratory adaptations allow them to survive in environments where dissolved oxygen in water is low or absent.
Movement on land varies but involves powerful body and fin coordination. Walking catfish and snakeheads primarily use body undulation and pectoral fin support to “wiggle” or “slither” across surfaces. Mudskippers and climbing perch leverage their strong pectoral fins as propulsive structures, effectively “walking” or “climbing” over obstacles. Some species, like the climbing perch, use spines on their gill covers to aid in terrestrial locomotion.
Reasons for Leaving Aquatic Environments
Fish venture out of water due to various ecological pressures and survival advantages. A primary motivation is often to escape deteriorating aquatic conditions, such as drying ponds or stagnant water bodies with low oxygen levels. Migrating overland allows these fish to seek new, more hospitable habitats with better water quality and higher oxygen concentrations.
Another significant reason is to evade aquatic predators. By moving onto land, even for short periods, fish can access areas inaccessible to larger water-bound threats. Terrestrial excursions also provide opportunities for foraging, allowing them to access food sources like insects or worms unavailable in their aquatic environment. These behaviors represent sophisticated survival strategies, demonstrating how certain fish species have successfully adapted to bridge the gap between water and land.