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Alien Species
Native Species

Mountain galaxias

Other common name(s): 
Scientific name: 
Galaxias olidus
(Günther, 1866)
Tarmo A. Raadik
Threatened but recovering

Formerly suspected to be an unresolved complex of morphologically similar taxa. This species has been recently revised and formally re-described (see Raadik 2014).


A small, elongate, tubular fish. Maximum recorded size to ~130 mm; commonly 60–80 mm. The body patterning is very variable, from bold patterning with bars and blotches to almost plain. The back is usually brownish to yellowish-green, and the belly is olive to silvery white. Scales are absent, the tail is truncate to weakly forked, and the anal fin originates under the dorsal fin from between 0.21 to 1.14 distance along the dorsal fin base (usually about 0.8 distance).  

The Mountain galaxias is also quite variable in body shape, with many populations recently identified and described as new species (see Riffle, Obscure, Barred and Stocky galaxias accounts).  

Biology and Habitat

Mountain galaxias are found in a variety of habitats from small creeks to large rivers. The species can occur with other members of the Mountain galaxias complex such as Stocky, Obscure and Barred galaxias but often it is the only fish species present in small upland streams. It is often observed in schools in slower flowing or pool habitats where trout are absent. In situations where trout are abundant, galaxias may be restricted to very shallow edge habitats, amongst dense aquatic vegetation, rocks, or timber debris and riffles.

It occurs at a variety of elevations within the Murray-Darling Basin, from near sea level to small montane streams, and along with the Kosciuszko galaxias (Galaxias supremus) is the only native fish that is found in the alpine zone above the snowline during winter. It has been recorded as high as 2137 m asl in the Snowy River drainage, only 91 m lower than the peak of Mt Kosciuszko and is present in Lake Cootapatamba (~2030 m asl) in the upper Murray River.

Individuals mature at the end of their first or in their second year. Spawning season varies across its range: from May-September in Vic and southern NSW/ACT; August to October in northern NSW and southern QLD. A small proportion of fish may spawn in autumn. Egg masses are found on the underside of stones at the head of pools and in riffles. Up to 1275 mature eggs have been recorded in an 85 mm female. Partially-spent females are rarely encountered, indicating that all eggs are laid at once, with 9 to 400 eggs (mean of 92) recorded in a sample of 10 individual egg masses in the ACT. After spawning eggs are ~2.5 mm diameter and hatch in about three weeks.

Larvae are ~10 mm long at hatching and juveniles reach ~35–40 mm length in their first year. Mountain galaxias can be lightly to heavily infected with small cysts (often grey or black) which are trematode metacercariae, embedded in the skin. In permanent streams in the ACT the species is thought not to migrate, and has a relatively small home range of ~19 m. However, in intermittent streams in Vic the ability to recolonise from deeper refuge pools suggest that larger movements can occur.

The species has been recorded basking and climbing on damp rocks out of the water in alpine areas, and climbing up a waterfall, a 20 m high dam wall, and a moist rock wall. This is aided by special structures on pelvic and pectoral fins which maximise the use of water surface tension, similar to those in the Climbing galaxias. Diet consists mainly of aquatic insect larvae, but terrestrial insects that fall onto the water from overhanging vegetation may form ~20% of the diet.

Distribution and Abundance

Mountain galaxias are widely distributed throughout south-eastern Australia, from southern Qld through to several catchments of the Eastern Mt Lofty Ranges in SA. They are not restricted to the mountains, being also found in lowland habitats, though in lower abundance. However, other galaxiids such as the Common galaxias are more abundant and widespread in lowland rivers in the Basin. As with other galaxiid species, where trout are present the abundance of Mountain galaxias is greatly reduced in lowland streams and eliminated from many upland streams. In such situations galaxiids are only found above waterfalls or swamps that prevent trout access.

Experiments to remove Rainbow trout from a section of Lees Creek in the ACT (1992), and, Brown trout, from Raspberry Creek in VIC (1995), resulted in the recolonisation by galaxiids of the trout-free sections of stream, with galaxiids still present and trout absent from Lees Creek some 30 years later.

Mountain galaxias was the most abundant and widespread galaxias species in the Basin with 6680 individuals recorded from the Sustainable Rivers Audit (2004–2013) across 14 river valleys. As its name suggests, it was abundant in montane and upland elevational zones (39% each of the species catch), followed by slopes (22%). 1898 individuals have been captured from 12 river valleys in the MDB Fish Survey (2014/15–2021/22).

Potential Threats

Continued spread of alien species, particularly trout, is the major threat to local galaxiid populations. The effects of the Climbing galaxias—which has been transferred to inland waters via the Snowy Mountains Scheme—on natural galaxiid populations is unknown, but competition, predation or displacement is possible. Infection with the alien parasitic copepod Lernaea cyprinacea (anchor worm) has been shown to cause significant mortality.

The 2017-19 drought threatened some local, isolated populations with a rescue occurring in the upper Condamine catchment in 2020.  

Parasites on a Mountain galaxias. Photographer: Mark Lintermans.
< Mountain galaxias - parasites - Mark Lintermans.jpg >

General References

Allan et al. 2018; Allan & Lintermans 2021; Berra 1973; Bond 2004; Cadwallader et al. 1980; Cook et al. 2019; Dexter et al. 2014; Ebner et al. 2020; Green 2008; Lintermans 2000, 2002; Lintermans and Raadik 2003; Lintermans et al. 2021; McDowall 2006; McDowall & Fulton 1996; Raadik 2011, 2014, 2019b; Shelley et al. 2021; M. Lintermans unpubl. data.

This species account is an extract from Fishes of the Murray-Darling Basin (second edition) and should be cited as "Lintermans, M. 2023, Fishes of the Murray–Darling Basin, Australian River Restoration Centre, Canberra."

Other Fish in this family

Front book cover of Fishes of the Murray–Darling Basin

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