These fish were made for walking: morphology and walking kinematics in balitorid loaches

Crawford, C.H.

Record Number:
New Jersey Institute of Technology and Rutgers, The State University of New Jersey, Doctor of Philosophy
Terrestrial excursions have been observed in multiple lineages of marine and freshwater fishes. These ventures into the terrestrial environment may be used when fish are searching out new habitat during drought, escaping predation, laying eggs, or seeking food sources. The physiological demands for life under water and on land are vastly different and require different functional adaptations. Fish with terrestrial excursions must be capable of dealing with the stresses of both aquatic and terrestrial environments for varying periods of time. To deal with these stresses, amphibious fishes exhibit many morphological and behavioral adaptations. These adaptations have led to a range of locomotor strategies when traversing the terrestrial environment. Importantly, a broader understanding of the ecomorphology and biomechanics of terrestrial excursions in living fishes will aid in interpretation of both fossil fish and early tetrapod anatomy and trackways. The rheophilic hillstream loaches (Balitoridae) possess a pelvic morphology which are attributed to adaptations for life in rapidly flowing water. The unique connectivity of the pelvic plate to the vertebral column via a sacral rib, and the relative size and shape of the sacral rib, fall within a spectrum of three discrete morphotypes. These morphotypes, determined through skeletal morphology and compared phylogenomically, are correlated with patterns observed in the pelvic muscle morphology of these fishes and are expected to provide a mechanical advantage for generating force against the ground. The skeletal connection via the sacral rib in balitorid loaches is hypothesized to facilitate terrestrial locomotion observed in the family. Field and laboratory-collected high-speed video is used to analyze terrestrial walking kinematics in seven balitorid species representing both subfamilies and two of the three morphotypes. Contrary to the hypothesis that robustness of the sacral rib would strongly influence walking performance, there is not a large reduction in walking ability in the Morphotype 1 representative. Major differences in walking kinematics distinguish the two balitorid subfamilies; with a generally greater walking performance in Balitorinae and reduced capability in the Homalopteroidinae representatives. The connection between internal anatomy and locomotion on land are explored with digitized video analysis, μCT scans, and in the context of the phylogenetic history of this family of fishes. The unexpected result of Homaloptera parclitella being capable of walking with comparable performance to other balitorids prompted further exploration into the walking mechanics in this species. To assess changes in terrestrial walking gait, walking kinematics are explored at experimental inclines (0˚, 15˚, 30˚, and 45˚) along with electromyography (EMG) during flat walking. H. parclitella is capable of walking at inclines without much change to the distance traveled over time. Additionally, another walking behavior is described; termed high walking, where the fish lifts its entire body off the substrate and carries its mass on its fins.
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