PACE, C.M.; Northern Arizona University: Pectoral fin use on land and water in the mudskipper Periopthalmus argentileatus.

Amphibious fish are superb organisms for studying biomechanical contrasts between aquatic and terrestrial locomotion. Perhaps the most well studied amphibious fish is the mudskipper, as it exhibits the extreme end of the amphibious continuum, with some species actually spending more time out of water than in water. While there have been past descriptions of mudskipper locomotion, they were largely qualitative and did not explicitly compare locomotion in divergent habitats. It is known that mudskippers use pectoral fins for terrestrial and aquatic locomotion. During terrestrial locomotion the pectoral fins synchronously protract and then retract to generate thrust. While swimming the pectoral fins are used for paddling (during slow locomotion) and steering. We hypothesized that the kinematics of terrestrial movements of the pectoral fins are significantly different than the kinematics of aquatic movements. Both lateral and ventral views of aquatic and terrestrial trials were filmed at 125 frames/second using a high-speed digital camera system. Sequences were digitized in NIH image and three dimensional coordinates were calculated. Mudskippers have a unique pectoral fin where the radials protrude from the body wall to form a fin that effectively has two joints. In terrestrial locomotion, the most proximal of these joints (the basal lobe formed by the radials) is anteriorly extended farther than in aquatic locomotion, and therefore increases the stride length of each pectoral fin during retraction. In contrast, aquatic pectoral fin use is characterized by extended rays, such that the fin surface area is much larger than that in terrestrial locomotion. As representatives of amphibious fishes, mudskippers demonstrate one way of balancing the demands of terrestrial and aquatic locomotion.