LIAO, J.: Locomotion in needlefish: anguilliform swimming with fins

Anguilliform locomotion involves the undulation of an elongate body axis and is characteristic of a diverse array of vertebrates, ranging from fishes to salamanders and reptiles. The Atlantic needlefish, Strongylura marina, is an elongate fish that displays anguilliform locomotion and also possesses a typical percomorph fin arrangement. While detailed body kinematics have been described for various anguilliform swimmers, no work has integrated the movement of the appendages during this mode of locomotion. In order to assess the role of the fins during anguilliform locomotion, I swam four needlefish (mean total length L= 24cm)in a flow tank at eight speeds (0.25- 2.0 Ls^-1) and captured simultaneous images of the ventral and posterior view using two synchronized high-speed video cameras. From these images I analyzed the kinematics of the body, pectoral fins, dorsal and anal fins, and caudal fin. Preliminary data show that at the lowest speed the pectoral fins oscillate at 3.7 Hz, while during the highest speed the pectoral fins are held flush against the body. The dorsal and anal fins move synchronously and are out of phase with body undulations at the lower speeds, leading the body during lateral excursions in a manner that suggests active control. At the lowest speed the tail oscillates at 2.8 Hz, while at the highest speed the tail oscillates at 6.0 Hz. A large (133%) increase in the maximum lateral tail displacement is observed across the range of speeds (atypical of teleost locomotion), from 2.4% L at the lowest speed to 5.6% L at the highest speed. Analysis of the trailing edge of the caudal fin at the lowest speed shows that the dorsal lobe leads the ventral lobe, while at the highest speed both the dorsal and ventral lobes oscillate at the same rate.