The question of whether fish walk seems simple, but the answer is surprisingly nuanced. While most fish propel themselves using buoyancy and fin movement in the water, many species have evolved unique mechanisms that fit the definition of walking: using specialized appendages to push off a solid substrate. These adaptations allow for movement that conserves energy, provides stealth, or facilitates terrestrial exploration. This form of locomotion often occurs where swimming is inefficient or impossible.
Benthic Locomotion
The most common form of “walking” in fish occurs on the seafloor, known as benthic locomotion. These bottom-dwelling species utilize highly modified fins as appendages to maneuver across the substrate rather than swimming. This adaptation is common in species that hunt slow-moving prey or live in complex, turbulent environments where swimming is energetically costly.
The handfish, found exclusively around Australia, exemplifies this movement; they use their large, fleshy pectoral and pelvic fins like hands or feet. These fins are elongated and highly muscularized, allowing the fish to “perch” or slowly shuffle along the ocean floor. Their preference for walking over swimming is likely due to the absence of a swim bladder, which makes maintaining buoyancy difficult.
Other species, such as flatfishes, demonstrate a specialized form of benthic walking. They use sequential portions of their long dorsal and anal fins as numerous tiny “fin-feet” that push against the sediment in a continuous metachronal wave. This movement is hydrodynamically cryptic, creating less water disturbance than traditional swimming, which helps them remain undetected. Deep-sea species like the tripodfish use elongated rays from their pelvic and caudal fins to stand on the abyssal plain like a tripod, waiting for prey.
Fish That Walk on Land
A more literal interpretation of walking is found in amphibious fish that can move on dry ground, often to seek new water sources, find food, or escape predators. The mudskipper is a famous example, spending a majority of its life out of water on tidal mudflats and mangrove swamps. These fish use their highly muscular and jointed pectoral fins as crutch-like appendages to perform a series of “push-ups” that propel them across the mud.
Their locomotion is distinct from the body wriggling seen in other amphibious fish because their fins possess joints analogous to the elbow and shoulder of land animals. Mudskippers also use their powerful tails to execute a launch known as a C-start, allowing them to skip or jump considerable distances. This terrestrial skill is supported by their ability to breathe air using modified gill chambers and skin.
The walking catfish, native to Southeast Asia, is known for its overland travel. This species uses snake-like body undulations and the stiff spines of its pectoral fins to maintain traction and push itself forward. The catfish can survive out of water for many hours thanks to specialized air-breathing organs, often undertaking nocturnal treks to colonize new ponds or marshes. Unlike the purposeful, fin-driven gait of the mudskipper, the catfish’s movement is a generalized crawl, using its fins primarily for support and leverage during the serpentine motion.
The Evolutionary Significance of Walking Fish
The adaptations seen in modern walking fish offer compelling insights into one of the most significant transitions in life’s history: the movement of vertebrates from water to land. This event, which occurred around 400 million years ago during the Devonian period, was initiated by lobe-finned fish that gave rise to the first four-limbed land animals, or tetrapods. The specialized fins of today’s walking fish act as living models for the evolutionary pressures that drove this change.
Fossil evidence from species like Tiktaalik, often called a “fishapod,” shows fins that were already adapting for interaction with the substrate, suggesting the initial steps toward walking happened in shallow water. The internal bone structure of these ancient fins became more robust and articulated, shifting their function from purely hydrofoil-like swimming to bearing weight and pushing off the bottom. This transformation involved changes in both the endoskeleton (corresponding to our upper arm and forearm bones) and the dermal skeleton (which forms the fin rays).
Genetic studies on modern fish, such as zebrafish, have revealed that the underlying genetic machinery required to develop limb-like structures may still be present. Researchers have shown that small genetic mutations can cause a fish’s pectoral fins to develop new, articulating bones, similar to an elbow joint, demonstrating a latent potential for limb formation. These findings suggest that the capacity for fin-to-limb transition is not entirely lost in most fish lineages, but is a developmental program that can be reactivated, providing a powerful parallel to the evolutionary path taken by our distant ancestors.