Abstract

The swimming abilities of adult golden perch, Macquaria ambigua (Richardson) (Percichthyidae) (441±16 mm, mean total length+s.d.), and adult silver perch, Bidyanus bidyanus (Mitchell) (Teraponidae) (258 ±10 mm, mean fork length ± s.d.), were tested in an experimental vertical-slot fishway. These two Australian species are potamodromous, and the adult fish move upstream large distances. Golden perch readily used the vertical-slot fishway, and a 20-min NV90 (the maximum water velocity that 90% of the fish in a sample can negotiate in 20 min) of 1.83 m s^-1 (95% confidence limits 1.43-2.03 m s^-1) is recommended for fishway design in the Murray-Darling river system. This velocity equates to a 171-mm step height between fishway pools and should be applied to a minimum pool size of 3 m (length) by 2 m (width) to avoid excessive turbulence. Lower velocities and larger pools might be necessary for long fishways or where there are large migrations of fish. Some silver perch used the fishway, but the results for this species were inconclusive. Fish were re-used at different velocities during the experiment, and a learning trial indicated that the number of fish negotiating the fishway increased with repeated use of the fish.