Effects of Flow Velocity on Feeding Behavior and Microhabitat Selection of the Stone Moroko Pseudorasbora parva: A Trade‐Off between Feeding and Swimming Costs

Abstract

AbstractWe conducted a series of experiments in a flume with a cavity that provided refuge from the current to assess the feeding behavior of the stone moroko Pseudorasbora parva. Feeding behavior on commercial food pellets was quantified by assigning fish activity to one of the components of their predation cycle: pause, moving, pursuit (i.e., approach, chase, and attack), coasting, and resting within the cavity. Swimming speed was highest during attack, followed by that during chase, moving, approach, and coasting. As flow velocity increased, the approach and moving distances decreased while swimming speed increased. The body angle of a fish in pursuit relative to the flow generally increased in the latter stages of approach, chase, and attack and markedly decreased as flow increased. When flow velocity increased, the percentage of lateral captures decreased and fish rested in the cavity longer. Thus, the average energy cost of a feeding fish did not increase in higher flow velocities as much as was expected from estimations made at low flow velocity. The processes of approach, chase, and attack were defined as the unsteady swimming motions of linear or centripetal acceleration. Energy expenditure in the unsteady swimming mode was estimated using the theory of hydrodynamics. The main energy expenditure of the feeding cycle shifted from moving in slow flow to chase in fast flow because search time was shorter in fast flow. The net energy gain from feeding and swimming implied that the fish used in this experiment tended to express specific behaviors based on the trade‐off between food uptake and energy expenditure up to a flow velocity of 7 cm/s. However, in faster flows, fish seemingly avoided a large drag force from the flowing water even if the net energy gain was positive.