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Mechanical Properties of the Dorsal Fin Muscle of Seahorse (Hippocampus) and Pipefish (Syngnathus)

Summary: Mechanical Properties of the Dorsal Fin Muscle of
Seahorse (Hippocampus) and Pipefish (Syngnathus)
Department of Biology, Wake Forest University, Winston-Salem, North Carolina
ABSTRACT The dorsal and pectoral fins are the primary locomotor organs in seahorses
(Hippocampus) and pipefish (Syngnathus). The small dorsal fins beat at high oscillatory frequencies
against the viscous medium of water. Both species are able to oscillate their fins at frequencies likely
exceeding the point of flicker fusion for their predators, thus enhancing their ability to remain
cryptic. High-speed video demonstrated that seahorse dorsal fins beat at 3042 Hz, while pipefish
dorsal fins oscillate at 1326 Hz. In both species, the movement of the fin is a sinusoidal wave that
travels down the fin from anterior to posterior. Mechanical properties of seahorse and pipefish dorsal
fin muscles were tested in vitro by the work loop method. Maximum isometric stress was 176.1 kN/
in seahorse and 111.5 kN/m2
in pipefish. Work and power output were examined at a series of
frequencies encompassing the range observed in vivo, and at a number of strains (percent length
change during a contractile cycle) within each frequency. At a given strain, work per cycle declined
with increasing frequency, while power output rose to a maximum at an intermediate frequency and
then declined. Frequency and strain interacted in a complex fashion; optimal strain was inversely


Source: Ashley-Ross, Miriam A. - Department of Biology, Wake Forest University


Collections: Environmental Sciences and Ecology; Biology and Medicine