Comparison of Fish-Passing Characteristics Between Vertical-Slot Fishway and Bilateral-Symmetric Multi-Slot Fishway

A novel bilateral-symmetric, multi-slot fishway (BMSF-R11) was recently developed, which has more migration space for fish, and lower mainstream velocity and turbulence than traditional vertical-slot fishways (VSFs) under the condition of the same slot width. This study aims to verify that, relative to a VSF, the BMSF-R11 is more favorable for the upstream migration of moderately swimming fishes. Three-dimensional numerical simulations were performed to determine hydrodynamic properties in both a VSF and the BMSF-R11, and laboratory fish-passage experiments using silver carp (Hypophthalmichthys molitrix, a moderately swimming fish species) were conducted to provide fish-passing characteristics. As expected, the BMSF-R11 possessed much higher fish-passing efficiency than the VSF (e.g., the passage success rate (PSR) was 90–93% vs. 57–63% and the entrance efficiency (EE) was 90–98% vs. 55–63%), due to the former’s much better hydrodynamic performance. There are two primary roughly linear fish-passing paths in a VSF, but four primary S-shape fish-passing paths are present in the BMSF-R11. Furthermore, this study reveals the inherent relationships among fish-passing efficiency parameters, fish-swimming trajectory, fish-occurrence frequency, and hydrodynamic properties in both a VSF and the BMSF-R11. This study contributes to conserving fishery resources and aquatic biodiversity, especially for migratory fish with moderate swimming abilities.