Spotted galaxis fish swims in just two rivers
Occupying just a 2-4km stretch of two rivers in Western Australia, the spotted galaxias is already presumed extinct in other known habitats
AUSTRALIAN CONSERVATION STATUS (EPBC Act)
The spotted galaxias inhabits both the Angove River and the Goodga River in the south-west of WA.
Spotted galaxias, western spotted galaxias, western trout galaxias, western trout minnow
The spotted galaxias occupies shallow streams which are generally between 0.5 to 5m wide. The species often dwells near rocks, plants or logs around the shoreline, especially in waterways close to the coast. The ideal habitat for the spotted galaxias is cool-climate, freshwater rivers. It appears the species is sensitive to warmer waters, which may account for its limited distribution.
Species truttaceus hesperius
Ranging in colour from brown to olive with darker spots along its side, the spotted galaxias also has a dark diagonal stripe below its eye. The species lacks scales, and its fins tend to be red-to-orange in colour. The spotted galaxias has an elongated body shape, and grows up to 12-14cm long.
The spotted galaxias is a sub-species, as data has found substantial genetic differences between these western populations and their eastern cousins. The individuals in the Goodga River in WA are typically shorter, while the species in Tasmania often grow longer than 14cm. Over 30 Per cent of the Tasmanian population are older than three years, compared to just three per cent of the Goodga River colony.
The spotted galaxias feeds off insects that fall on the water surface, such as spiders, flies and grasshoppers. The species also preys on small decapods, such as shrimp, and other smaller fish. Larvae consume plankton in the lake in which they are hatched.
Although the populations in the Angove and Goodga rivers seem to be landlocked, spotted galaxias populations could also be diadromous, meaning they could migrate between freshwater catchments and the sea. Landlocked colonies use lakes as nursery areas, with juveniles migrating to the river after growing to around 25mm in size.
Previously, the spotted galaxias occupied catchments of the Kalgan and King rivers near Albany, WA; however, recent surveys have failed to locate any specimens from the areas and the species is presumed extinct. The population in the Goodga River is limited to a 4km stretch of water; the Angove River population a mere 2km. Both areas are restricted by weirs, with the combined area of occupancy calculated at just 0.012 sq. km.
Threats to the spotted galaxias
The introduction of species such as the rainbow trout, brown trout and mosquito fish has had a severe impact on spotted galaxias populations. Introduced species compete with the spotted galaxias, and the mosquito fish in particular is renowned for preying on native fish – though the Goodga and Angove Rivers are currently free from mosquito fish.
Both populations of spotted galaxias are effectively trapped by weirs. In the Goodga River, the weir prevented the spotted galaxias from traveling upstream to the traditional spawning ground. As a result, large numbers of the species gathered at the base of the weir, putting them at risk of predation by birds. In response, a fish ladder was constructed in 2003, allowing the population to migrate a further 2km upstream.
The infection of the Goodga River population by the parasite Ligula intestinalis has also played a part in the population decline. Infection can cause physical deformities, and also reduces the species’ swimming ability, making them easy prey for birds. It appears that the spotted galaxias are infected as larvae in the nursery lake, as no fish over 8mm have been found infected with the parasite.
Land clearing in areas near the river catchment zone has resulted in an increase in both water and salinity levels, which can lead to an increase in water temperature that may be detrimental to the spotted galaxias. The species is now extinct in both the Kalgan and King rivers, which is thought to be a consequence of the increased salinity in both catchments.
Recovery plans for the spotted galaxias
The Threatened Species Scientific Committee created an action plan in 2006, which aimed to address the threats affecting the spotted galaxias. In addition, the Western Trout Minnow Recovery Plan was introduced in 2008, which aims to lessen the effects of existing threats as well as sustain or increase the populations of spotted galaxias. The habitat of the spotted galaxias is also protected by the Two Peoples Bay Nature Reserve Management Plan, which restricts public access to the Angove River.