Restoration practices aimed at fish habitat enhancement often include installation of instream structures. However, mixed outcomes have been reported regarding structure effectiveness, while mechanisms underlying success remain unclear. The interactions between fish and flow conditions generated by instream structures and their subsequent impact on fish energetics, may provide some insight. This study seeks to quantify how restoration structures, simulated by cylinders in three orientations, alter the energetics and swimming stability of smallmouth bass (Micropterus dolomieu). Accelerometers measured swimming stability, while a respirometer measured energy expenditure at multiple velocities. Particle image velocimetry was used to characterize flow fields behind structures. Structures generated flow conditions that benefited fish energetically. Fish had a smoother gait and expended less energy when swimming near a structure, regardless of its orientation. Benefits varied with flow conditions; reductions in energy expenditure were especially apparent at high flow velocities. Results suggest that restoration structures may be most energetically beneficial in stream systems with consistently high velocities, and inform restoration by indicating flow conditions in which structures provide the greatest energetic benefits for fish.

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