O’NEILL, M.W.*; GIBB, A.C.: Do flatfish fin rays function like millipede legs? The kinematics of “walking” in Synaptura salinarum.

Flatfish locomotion is poorly understood and represents a significant gap in our understanding of aquatic locomotion. Currently, the only work in this area has examined escape responses. We attempt to describe the typical mode of locomotion for many flatfish, the walking motion used to move over the substrate. This motion has been observed in several species, and likely represents the most common form used by these fishes. Morphological observations of flatfish dorsal and anal fins suggest that fin rays may be functionally equivalent to millipede legs (Diplopoda). As described by Manton in the middle of the 20^th century, millipede locomotion involves multiple appendages producing cyclic waves of motion with two or more feet in contact with the ground at several fixed points. We hypothesize that a flatfish moving slowly over the substrate will use its dorsal and anal fin rays in a manner similar to millipede legs. Slow-speed locomotion of Synaptura salinarum, a small freshwater soleid, was recorded using a Redlake PCI 1000S digital-video system, and images were analyzed using a custom digitizing program. Image analysis reveals that S. salinarum does not use multiple waves of fin ray movement in its slow benthic walking mode. The dorsal and anal fin rays create a fixed point approximately two-thirds down the body. As this occurs, the fish raises its head slightly and pushes posteriorly with the dorsal and anal fins. As the fish moves anteriorly, the fixed point moves posteriorly toward the caudal fin. Thus, when walking this flatfish species does not produce multiple, continuous traveling waves similar to those seen in millipedes; instead, it uses two fixed points on the fins to produce horizontal and vertical thrust.