Biomechanics of fin/body interactions in fish propelled by undulatory median and/or paired fins

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The relationships between structure and function in animals can effectively be addressed from the standpoints of both biology and physics. This integration forms the basis of the science of biomechanics. The mechanics of fish swimming (how a fish interacts with the water to produce propulsive forces), energetics (the associated energy) and efficiency (how much energy is wasted) are well understood for fish that swim by undulating their body. This has allowed for an understanding of perfomance in relation to form and muscle powering. For example, the endurance of migrating salmon, the high sustained swimming speed of tuna and the rapid acceleration of pike as they catch their prey. However, less is known about the mechanics and energetics of fish that have a rigid body carapace and swim by undulatory motions of their fins (e.g. trunkfish, boxfish and pufferfish). My previous studies have identified a variety of adaptations that allow these forms to move efficiently at relatively low speed through complex and cluttered environments such as coral reefs. This study focuses on a number of energetically advantageous mechanical interactions between the fish's propulsive fins and its body. Theory suggests that an undulating sheet-like fin attached to a rigid body produces more thrust than the same fin executing the same motions "on its own". The purpose of this study is to experimentally confirm this effect and assess its magnitude and energetic consequences in a variety of "non-bodied swimmers". Recently, engineers have turned to biology for solutions to practical problems (bioinspiration) and boxfish and their relatives are good models for certain autonomous underwater vehicles that may be used in environmental monitoring (e.g. detecting pollutant concentrations and sources, military applications, ocean surveying) and this work will likely contribute to the design and operation of such vehicles. In particular, undulatory fins offer high efficiency and manoeuvrability. Energy savings through positive hydrodynamic interactions between the propulsor and body being propelled may protract vehicle battery life and thereby mission duration.