Attracting juvenile fish into Tube Fishways - roles of transfer chamber diameter and flow velocity

Freshwater fish populations around the world are in decline, with barriers impeding essential migrations for many species. To restore fish passage, the novel Tube Fishway attracts fish into a cylindrical transfer chamber, then lifts them at near-atmospheric pressure via a surge of water. We investigated fish attraction into transfer chambers of different diameters, with varying attraction flow velocities, to identify the scalability of the system as well as the optimum attraction conditions. Three transfer chambers, with diameters of 0.1, 0.225, and 0.4 m, were tested under attraction velocity conditions between 0 and 0.5 m/s. Repeated experiments were conducted with juveniles of two native Australian species, silver perch (Bidyanus bidyanus) and Australian bass (Percalates novemaculeata) for each configuration of diameter and flow. Fish were acclimated to the equipment, then their entry into the transfer chamber was monitored and recorded with video cameras. About twice as many silver perch as Australian bass were attracted into the transfer chamber, but follow-up experiments with smaller bass showed improved attraction (by up to 40%). Streamlining the entry design improved attraction for silver perch by up to 60%. Both species varied in their performance, with optimum attraction at a velocity of 0.15 m/s and transfer chamber diameter of 0.225 m. For this combination, fish attraction behaviour showed a "Search Phase " and "Occupation Phase ". Visual observations showed fish's preference for entering the transfer chamber near the bottom. There is considerable opportunity to build on these findings with other species and sizes to optimize fish attraction into Tube Fishways.