A moderate-sized, stout-bodied, scaleless fish with a longish head and large mouth reaching back to below the front of the eyes. Maximum size >200 mm; usually 120–140 mm. The anal fin is positioned directly below or slightly behind the dorsal fin, and the tail is slightly forked. The dorsal, anal and caudal fins are golden to orange, with a dark rear fringe.
The back is a brownish to deep-olive, fading to brownish-grey on the sides and silvery on the belly. Large, round purplish spots are present on the upper sides and back, each surrounded by a lighter halo. There is a distinct dark diagonal stripe extending down from the bottom of the eye.
In its natural lowland coastal habitats, the Spotted galaxias favours cover such as logs, boulders, and overhung banks on the edges of pools. Coastal populations spawn in autumn–winter, and the larvae have a marine phase of several months before returning to estuaries as 45–65 mm whitebait in spring. In landlocked populations spawning occurs in spring after an upstream migration into feeder streams, and the larvae fulfilling their pelagic phase in downstream lakes. In a landlocked population in WA, juvenile fish have been recorded jumping and climbing to overcome a small weir, and adults commonly use a fishway in their upstream spawning migrations, but little is known of their movement ecology in the Basin.
Fecundity is moderate to high: 1000–16,000 eggs deposited amongst instream aquatic vegetation. The eggs are small (~1.0–1.3 mm diameter) and take about four weeks to hatch, and the larvae are about 6.5–9.0 mm long at hatching.
Spotted galaxias are carnivorous—adults eat aquatic insect larvae and terrestrial insects that fall onto the water surface. They take much of their food in the drift in midwater, particularly caddisflies and mayflies. The larvae feed mainly on microcrustaceans (copepods) for the first 2–3 months of life. Experimental trials have shown that Spotted galaxias are potentially an effective mosquito mitigation measure. They consumed more mosquito larvae at 15 and 20°C and were equally effective consumers of mosquito larvae as Gambusia at 25°C.
There are significant differences in the ecology of the coastal and landlocked populations of this species in Tasmania, including morphology, different timing of the breeding season and the presence of more young fish in coastal populations. There are also significant differences between landlocked Tasmanian and landlocked Western Australian populations: the Tasmanian fish mature later; live longer; grow larger and have larger eggs and larvae. The WA population has the late-autumn spawning season of the coastal Tasmanian fish.
Little is known of the species’ ecology in the Basin, but it must be assumed that the Basin populations are landlocked given the large numbers of migration barriers between the Campaspe and marine waters.
Normally a species of coastal streams of Vic, Tas and southwest WA, in the Basin the Spotted galaxias is present in the upper Campaspe and Loddon drainages, where it is thought to either have been transferred from coastal Victorian streams through its use for bait, being first recorded in the Basin from a water supply dam near Castlemaine frequented by coastal anglers during the early 1990s; or to represent a remnant population of a historically wider distribution.
Only 7 individuals (out of a total of 218,441 fish) were recorded in the Sustainable Rivers Audit sampling of the Basin from 2004–13, all found in the upland zone (400–700 m asl) of the Campaspe drainage. The species was not recorded in the MDB Fish Survey (2014/15–2021/22). Based on an illustration and aboriginal knowledge, the early ichthyologist Wilhelm Blandowski likely recorded this species near the junction of the Murray and Darling rivers in 1856/57. A single recent record of a whitebait of this species is also known from the Lower Murray near Wentworth.
Predation and displacement by introduced trout species, and habitat loss through deforestation are threats. In coastal streams, barriers to fish passage between marine and freshwater and within freshwater are a threat. In WA increases in water temperature and habitat sedimentation have potentially eliminated some populations. The WA population may also be threatened by a parasite which affects swimming ability and fecundity of individuals. When translocated, the Spotted galaxias may itself pose a threat to other native fish species through competition for food or space.
Allen et al. 2002; Amtstaetter et al. 2017, 2021; Cadwallader & Backhouse 1983; Close et al. 2014; Gilligan 2005b; Humphries 1989, 1990, 2009; Humphries & Lake 2000; Lawrence et al. 2016; Littlejohn 2000; McDowall & Fulton 1996; Morgan 2003; Morgan & Beatty 2006, 2019. T. Raadik pers. comm.
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