Salinity tolerance during early development of threatened Murray hardyhead (Craterocephalus fluviatilis) to guide environmental watering

The worldwide reduction in wetlands has led to the large-scale decline of wetland-dependent species. In Australia, to redress some of the decline, partial restoration of the hydrology of a small number of wetlands has been attempted using allocations of environmental water. A common goal of the watering is the maintenance and enhancement of native fish communities, which historically have included populations of the salt tolerant Murray hardyhead (Craterocephalus fluviatilis), a small, short-lived fish, endemic to the lower Murray-Darling Basin. Despite the addition of environmental water to several sites at which the species is known to persist, populations continue to decline. This decline is, at least in part, suspected to be a consequence of salinities that conflict with the breeding ecology and survival of early life stages. Here the effect of salinity on egg hatch rate and the upper salinity tolerance of larval and juvenile Murray hardyhead was determined under laboratory conditions. It was found that eggs were vulnerable to elevated salinities, whereas juveniles were capable of tolerating salinities up to 105 ppt. Based on the results of the experiment, brackish wetlands managed for Murray hardyhead should be maintained, where possible, between 12 and 45 ppt. Such a salinity regime will necessitate less intensive management of salinity, and a reduced volume of environmental water, providing both environmental and fiscal benefits. The research highlights the benefits of investment in targeted research.