The sea robin, a marine fish, is known for its ability to “walk” across the seafloor. Unlike most fish that rely solely on swimming, these creatures use a unique form of bottom locomotion. They have large, wing-like pectoral fins and modified, finger-like rays. This behavior allows them to navigate their benthic habitat.
The Mechanics of Sea Robin Movement
Sea robins move along the seabed using three lower, detached, finger-like rays extending from each pectoral fin. These modified fin rays, which are not true legs, have separated from the main fin structure during development. They are independently controlled, allowing for coordinated, limb-like propulsion.
The movement resembles a walking motion, as the sea robin alternately pushes off the seafloor with these flexible rays. This enables precise control and flexibility, facilitating their unique mode of locomotion.
Beyond movement, these modified fin rays also serve a sensory purpose. They are covered in tiny projections called papillae, which are sensitive to touch. These papillae also contain taste receptors, allowing the sea robin to detect chemical cues in the sediment. This combination of tactile and chemosensory capabilities provides the fish with information about their immediate environment.
While sea robins are known for their “walking” behavior, they also swim. Their benthic locomotion using these specialized fin rays is a distinct and frequently observed mode of transportation, particularly when foraging. This dual capability allows them to adapt to different situations, transitioning between swimming through the water column and scuttling the bottom.
The Purpose of “Walking”
The primary reason sea robins engage in this “walking” behavior is for foraging, enabling them to efficiently locate hidden prey within the seafloor sediment. As they move, their sensory fin rays constantly probe the sand and mud. These rays, equipped with both touch and taste receptors, allow them to detect buried organisms without relying on visual cues.
The northern sea robin (Prionotus carolinus), for instance, has shovel-shaped lower legs covered in papillae that are sensitive to touch and chemicals. This species is particularly adept at digging into the sand to uncover shallowly buried food items. Their ability to “taste” the seafloor helps them pinpoint prey like crustaceans, worms, and small fish that might be concealed from sight.
Studies have shown that sea robins can locate buried mussels or even capsules containing mussel extract, demonstrating the effectiveness of their chemosensory abilities. This specialized foraging method allows them to exploit a food source that is inaccessible to many other fish. The “walking” motion also helps them navigate complex seafloor environments, providing stability and maneuverability in their benthic habitat. This unique adaptation provides a significant advantage in their search for sustenance.