Feeding in Flow: Environmental Flow Conditions Alter Prey Capture Kinematics in Fish

AbstractVirtually all terrestrial, aerial, and aquatic organisms regularly interact with moving fluids. In marine and freshwater habitats, water flow is one of the most significant environmental variables impacting the ecology, behavior, biomechanics, and, ultimately, evolution of fishes. Although predatory fishes must attack prey rapidly and accurately across a range of flow conditions in nature, their feeding is almost always studied in still water. Thus, how fishes alter prey capture in response to ecologically relevant flow conditions remains poorly understood. Here, we determined how largemouth bass modulate prey capture across a range of flow speeds (0-60 cm/s) in a flume using high-speed videography. We tested an existing prediction that fishes should swim faster during prey capture in flow to increase momentum and damp external perturbations. If supported, separate established hypotheses state that fishes feeding in flow should also increase mouth expansion to circumvent decreases in strike accuracy associated with swimming faster. Indeed, largemouth bass swam faster and expanded their mouths more in high-flow conditions, which are kinematic changes consistent with maintaining capture success. Interestingly, they also altered the use of their pectoral fins, which are involved in braking, as flow speed increased. Our results reveal how flow, a widespread environmental variable, impacts the ecologically critical process of prey capture and yield important information about how species with high kinematic flexibility can maintain feeding performance in the face of changing environmental conditions.