Mountain galaxias

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Mountain galaxias species complex
Mountain Galaxias (1).jpg
A specimen of the mountain galaxias species complex, caught in an upland stream on a tiny barbless wet fly.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Osmeriformes
Family: Galaxiidae
Subfamily: Galaxiinae
Genus: Galaxias
Binomial name
Galaxias olidus
Günther, 1866
Galaxias fuscus
Mack, 1936

The mountain galaxias species complex is a group of freshwater galaxiid fish found all over southeast Australia. They form a cryptic species complex.


These fish were originally designated as a single species, Galaxias olidus, despite:

  • occupying a very wide geographic range
  • occupying a range of different habitats, from headwater rivulets at 1,800 m on the flank of Australia's highest mountain (Mount Kosciuszko) to large "midland" rivers and streams (or in other words rivers and streams at the upland/lowland transition, which may be extensive in Australia)
  • displaying a wide range of body forms and colouration

Ongoing research is now revealing them to be a species complex. In recognition of this, the mountain galaxias species complex has been referred to as Galaxias spp., although the designation Galaxias olidus will probably remain with one of the species in the complex. The mountain galaxias species complex also incorporates the barred galaxias (Galaxias fuscus) whose status as a distinct species was debated, but is now confirmed.


The mountain galaxias species complex occupies a vast geographical range. They are found from southern Queensland to the Adelaide Hills in South Australia, and while occurring widely in the Murray-Darling river system, are also found in eastern and southern coastal systems, as well. It is not clear how much of their coastal distribution is due to natural river capture events (although it is certain much of it is) and how much of it may be due to migration, for many mountain galaxias species have the ability to "climb" natural migration barriers with modified pelvic fin structures.

Within the Murray-Darling system, the mountain galaxias species complex continues the trend of specialisation into upland and lowland habitats, with species found in upland habitats, and the flathead galaxias found in lowland habitats. Though mountain galaxias species stray down to the upland/lowland transition zone in some rivers, mountain galaxias species are largely upland species. Indeed, they are the upland specialists, found in the smallest of streams and at higher altitudes in Australia than any other freshwater fish. Some fascinating microniche partitioning has occurred amongst the galaxiids in upland Murray-Darling habitats, this being one of the causes of the species complex.


The distribution of mountain galaxias species has been massively fragmented by the introduction of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss). Mountain galaxias have—with the exception of one remarkable newly discovered species that lives in water too fast for introduced trout—shown a complete inability to live with introduced trout species in upland habitats due to competition and predation, and extremely serious predation on mountain galaxias species by introduced trout has been documented. Countless localised extinctions of mountain galaxias species populations have happened due to introduced trout, and this is continuing to occur with illegal trout stockings.

Many mountain galaxias populations, possibly undescribed species or subspecies, face extinction, and many other populations, also possibly undescribed species or subspecies, have already been permanently lost.



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