The effect of depth on the interaction between perch (Perca fluviatilis) and minnow (Phoxinus phoxinus)

We tested the hypothesis that small fishes avoid piscivores by increasing their use of shallow water areas, thereby reducing the capture success of the piscivore. Experiments were conducted in 600‐1 aquaria, using perch (Perca fluviatilis) as the piscivore and minnow (Phoxinus phoxinus) as the prey. Two size classes of minnows, presented alone and together, were placed together with perch in aquaria with and without shallow water areas. The capture success of perch and use of depth by minnows changed as predicted by our hypothesis. In addition, we observed a decrease in the shoal size of minnows when perch were present. Perch selected large minnows over small minnows when both size classes were present, probably because large minnows were a more energetically profitable prey size.