Swimming ability of juvenile Australian bass, Macquaria novemaculeata (Steindachner), and juvenile barramundi, LAtes calcarifer (Bloch), in an experimental vertical-slot fishway

Abstract

Australian bass, Macquaria novemaculeata, and barramundi, Lates calcarlfer, are catadromous fish that spawn in estuaries and the juveniles migrate upstream into fresh water. Lowland fishways in the range of these species therefore need to accommodate these juvenile fish. The swimming abilities of three size classes (fork length (LCF) + s.d.: 40 * 3 mm, 64 + 5 mm and 93 + 8 mm) of juvenile Australian bass and one size class (43 4 mm total length) of juvenile barramundi were tested in an experimental vertical-slot fishway. Water velocity was calculated from the head loss in water level between adjacent pools in the fishway, using a coefficient of discharge (C_d) of 1.0. Both species readily negotiated the fishway at low water velocities, indicating that the fish were in a migratory mode and that these fish could use the vertical-slot design of the fishway. The sigmoidal decrease in this ability with increasing water velocity was described by a probit regression. The NV95 value (maximum negotiable water velocity for 95% of the sample) is suggested as the suitable maximum-velocity criterion for vertical-slot fishways for these fishes. The NV95 values were 0.66 m s^-1 for 43-mm barramundi, 1.02 m s^-1 for 40-mm bass, 1.40 m s^-1 for 64-mm bass and 1.84 m s^-1 for 93-mm bass. The NV95 for barramundi is probably an underestimate of their swimming ability in the wild because the water temperature was low for this species. Up to 20% of the 93-mm bass died at test velocities greater than 2.0 m s^-1, but there were no mortalities of other fish during or immediately following a trial. The results indicate that water velocity in fishways for juvenile bass and barramundi should not exceed 1.4 m s^-1 in a cell size of 1.5 m length and 1.0 m width. The relative swimming speeds (body lengths per second) of bass in the fishway are higher than other estimates of burst swimming speeds of juvenile fish obtained from studies in flumes. This indicates that data from the latter type of study should not be used to determine water velocities for fishways.