Six questions in fish locomotor biology and the technical approaches needed to address them

For nearly a century, fish have served as a model experimental system to understand how major organ systems both allow and respond to exercise. Experimental biologists have primarily evaluated the responses of organ systems to exercise by inducing fish to swim over a range of speeds. Flow tank and respirometry studies have been instrumental in contributing to our understanding of how fish alter kinematics and metabolism in relation to movement speed. As a guide to extending the considerable recent progress in understanding fish locomotor biology, this Commentary focuses on presenting six outstanding questions that we believe are relevant to continued progress in understanding the mechanisms of aquatic locomotion. First, field biomechanics: how can we obtain whole-body biomechanical data on locomotion from fish in the field? Second, stability: what are the morphological correlates of body stability in fish, and how metabolically costly is it for fish to maintain stability? Third, metabolism: how can metabolic measurements be used to understand the cost of swimming under different hydrodynamic conditions? Fourth, computation: how can we best use computational approaches to understand the biomechanics of fish locomotion? Fifth, robotics: how can robotic models help us to understand the physics of fish locomotion? Sixth, environmental flows: how do fish modulate their locomotor dynamics to deal with complex flow regimes that are more typical of natural conditions? These topics have broad potential impacts on research related to the anatomy and physiology of exercise behavior and ecology, as well as on responses by fish to future environmental challenges.