While most fish propel themselves through water with powerful tail strokes, the answer to whether all fish swim this way is definitively no. The diversity of aquatic life has led to a stunning array of alternative movements. Nature has evolved species that glide through the air, walk across the seabed, or simply remain motionless to survive. The methods fish use to navigate their environment are as varied as the habitats they occupy.
The Mechanics of Traditional Swimming
The most recognized form of fish movement involves a wave-like flexing of the body and the caudal, or tail, fin. This is known as body-caudal fin (BCF) propulsion, where muscles along the trunk contract sequentially to push water backward, generating forward thrust.
Fast, sustained swimmers, like tuna, exhibit thunniform movement, where the body remains mostly rigid and propulsion is concentrated in the crescent-shaped tail. This mechanism is highly efficient for speed, reducing drag by limiting body oscillation.
Slower or more maneuverable fish use larger portions of their bodies for propulsion. Eels, for example, use anguilliform movement, where a wave travels evenly down the entire long body. Many common species, such as salmon and trout, employ carangiform movement, concentrating the motion in the posterior half of the body.
For slower, precise maneuvering, fish utilize their paired (pectoral and pelvic) and median (dorsal and anal) fins, a method called median and paired fin (MPF) propulsion. Species like parrotfish often use their pectoral fins in a rowing motion, known as labriform swimming, to navigate complex reef structures.
Locomotion Outside the Water Column
Some fish have evolved specialized fins and behaviors that allow them to move in ways that barely resemble swimming. These adaptations often relate to accessing food, escaping danger, or navigating amphibious environments.
Flying fish use a burst of powerful traditional swimming to launch themselves completely out of the water. Once airborne, their large pectoral fins spread out to act as airfoils, allowing them to glide over the ocean surface for significant distances, a strategy used to escape aquatic predators.
Other species modify their fins to interact directly with the substrate, effectively “walking.” Mudskippers are amphibious fish that use their strong, muscular pectoral fins to crawl or skip across mudflats during low tide.
Similarly, bottom-dwelling frogfish use modified pectoral and pelvic fins to “stroll” along the ocean floor while hunting. This ambulatory locomotion is also seen in certain rays and skates, which use their small pelvic fins for a distinct, four-limbed saunter across the sand, sometimes called “punting.”
This reliance on fins for ground movement or air gliding highlights an evolutionary trade-off between maximizing speed in the water column and exploiting resources in niche environments. The little skate’s use of a synchronized left-right “walk” with its pelvic fins suggests that the neural control for this type of movement was present in fish ancestors long before vertebrates moved onto land. For creatures like the red-lipped batfish, walking is the primary mode of travel, as their body structure is poorly suited for typical undulatory swimming.
Fish That Prioritize Stillness
For a large group of fish, the most effective form of movement is intentional stillness. Many ambush predators conserve energy by remaining stationary, relying on camouflage and patience to capture prey.
The stonefish, for example, mimics a rock or piece of coral, waiting for unsuspecting prey before executing a lightning-fast strike. This sit-and-wait strategy is energetically efficient compared to actively pursuing prey.
Even when a bony fish with a swim bladder is hovering in the water column, it must constantly make small, corrective fin and body adjustments to maintain its position. This need to counteract instability means that hovering can require twice the energy of resting on the bottom.
Therefore, resting motionlessly on the substrate is often a preferred state for deep-bodied fish like pufferfish, allowing them to conserve energy while waiting for prey. Other fish, like seahorses, use specialized, rapidly fluttering dorsal and pectoral fins to maintain a vertical posture or drift slowly, relying on their prehensile tail to anchor themselves to vegetation rather than engaging in sustained swimming. These diverse strategies demonstrate that for many fish, swimming is not a constant necessity but one of several options for locomotion.