Locomotor variation of fishes: connecting energetics and kinematic modulation

Analyses of vertebrate locomotion have frequently revealed variations in locomotor energetics and movement both among individuals and through time within an individual. This variation is often collapsed into mean values for broad comparative analyses of function. However, kinematic patterns of locomotion, even when animals move at a near-constant mean speed, frequently vary with both the physical and biological context. Here, we demonstrate, using analyses of fish locomotion and energetics, how variation among individuals in kinematic gaits can manifest as changes in dynamics of metabolic rate (estimated from oxygen uptake). We present kinematic data from a small school of giant danio (Devario aequipinnatus) to show that fishes within a school frequently modulate their kinematics and change position, even when the school moves at an overall constant mean speed. We show that rainbow trout (Oncorhynchus mykiss), swimming over a range of speeds, exhibit considerable variation in tail beat frequency and metabolic rate among speeds. By experimentally altering the fluid dynamic environment, we demonstrate that brook trout (Salvelinus fontinalis) show correlated modulation of both kinematics and metabolic rate. Simultaneous measurement of energetic and biomechanical characteristics can unveil the physiological, biomechanical and fluid dynamic mechanisms that underlie dynamic changes in vertebrate locomotor gaits. This article is part of the theme issue 'Embracing variability in comparative physiology: why it matters and what to do with it'.