Injury-free transport of fish through closed conduit components

Fish can be transported through closed conduits including in hydropower systems, pipe-based fishways, and aquacultural transfer pipes. Fish can be injured when travelling through pumps and turbines, however, there is limited understanding of potential fish injuries in closed conduit systems more broadly. This study systematically investigated hydrodynamic conditions allowing injury-free fish transport through pipe components including smooth entrances, expansions, contractions, and 90-degree bends. Experiments under controlled laboratory conditions used two pipe diameters, five flow rates, and seven pipe components which resembled real-world components and flow conditions. Hydrodynamic parameters were measured with Lagrangian pressure and acceleration sensors, and live fish tests were conducted with juvenile silver perch (<i>Bidyanus bidyanus</i>), a representative Australian fish species. Entrances are locations of higher risk for fish injury due to high accelerations and pressure changes. Secondary flows caused more pronounced fish interactions at higher flow rates. Velocities should remain above swimming speeds to prevent exhaustion injury. For all configurations, fish travelled injury-free providing new safe hydrodynamic conditions for rapid pressure changes, accelerations, and shear stresses in pipe flows, and guidance to safely transport fish in closed conduit systems without passing through turbine or pump. Further research should consider additional species, fish sizes, and larger pipe diameters.