PACE, C. M.; GIBB, A. C.; Northern Arizona University; Northern Arizona University: Do mudskippers really �crutch�? Testing the inverted pendulum model in an amphibious fish.

The mudskipper is an amphibious fish that has the ability to locomote on land. Like most terrestrial vertebrates, mudskippers use their limbs to overcome gravity and propel their body forward. However, unlike most terrestrial vertebrates, mudskipper locomotion cannot be characterized as being bipedal, quadrapedal, or undulatory. Instead mudskippers use their pectoral fins to elevate the front half of their body off the substrate while propelling the entire body forward, a movement that has been compared to a human using crutches. An inverted pendulum characterizes human crutching, but there has never been an explicit analysis of mudskipper terrestrial biomechanics to determine if this is also true for mudskippers. Thus, we ask the question do mudskippers really �crutch�? To assess mudskipper biomechanics, mudskippers were filmed using high-speed digital cameras and the programs QuickImage and Quicksand were used to quantify movements. The duty factor for the mudskipper pectoral fins is approximately 0.6. Additionally, the bulk of forward displacement (93%) occurs while the mudskippers pectoral fin is in contact with the ground. As little forward locomotion occurs during the recovery phase of the pectoral fin, an inverted pendulum is unlikely to be an appropriate model for mudskipper locomotion. If mudskippers are not crutching they could be elevating their body to simply reduce friction incurred from drag. Therefore, we suggest that mudskippers use their pectoral fins to both drag and launch their bodies forward.