Western mud minnow - Galaxiella munda

Occurs in one tributary of the Moore River (north of Perth), one tributary of the Swan River (Perth), the upper Vasse River (south of Busselton), in the upper Margaret River, a few groundwater-maintained tributaries of the Blackwood River and a number of system between the Donnelly and Angove Rivers on the south coast.

The fragmented populations reflect what was once a much larger range, which is presumably a result of salinisation, land degradation, hydrological changes due to abstraction and climate change, and competition/predation from feral species. Fresh groundwater expression in streams appears to be a key factor in maintaining remnant populations. For example, the secondarily salinised main channel of the Blackwood River has shown to have genetically isolated populations that continue to exist in fresh tributaries in the catchment.

They prefer relatively undisturbed, permanent stream habitats (rather than the ephemeral wetland habitats where black-stripe minnow are typically found). Prefers small, gently flowing creeks and streams. Found in low pH environments (as low as pH 3), but had low salt tolerance (susceptible to salinisation).

Based on recent observations by the Healthy Rivers Program team, the western mud minnow is expected to be able to aestivate (a state of dormancy, characterised by inactivity and a lowered metabolic rate) to avoid drying and poor water quality, at least where soft sediments remain saturated.  This means it may have a higher resilience to the drying climate than previously expected. However, as its natural habitat includes small, shallows streams, it is also more at risk from a decline in streamflow and water levels.

Feeds primarily on small insects, insect larvae and microcrustaceans.

Extended breeding period from July to October. Females produce multiple batches of eggs during the season.

Life span is short, with most fish perishing after spawning (near the end of the first ear of life).

Threatened species: As of 5th March 2025 it is listed as vulnerable under the Biodiversity Conservation Act 2016 (state, Western Australia) and the Environment Protection and Biodiversity Conservation Act 1999 (Commonwealth). It is listed as endangered under the ICUN Redlist of Threatened Species 2019 (International).

Under the BC Act, Threatened species are listed in the category of critically endangered, endangered or vulnerable. Vulnerable species are considered to be “facing a high risk of extinction in the wild in the medium-term future, as determined in accordance with criteria set out in the ministerial guidelines”.

Salinisation is likely to have been the main driver of past reductions, however, recent contractions may have also resulted from reductions in surface and groundwater discharge and predation by introduced species, some of which have been stocked into its habitats.