Mountain galaxias
Encyclopedia
The mountain galaxias species complex is a group of freshwater Galaxiid fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 found all over southeast Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

. They form a cryptic species complex
Cryptic species complex
In biology, a cryptic species complex is a group of species which satisfy the biological definition of species—that is, they are reproductively isolated from each other—but whose morphology is very similar ....

.

Classification

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 metres on the flank of Australia's highest mountain (Mount Kosciuszko
    Mount Kosciuszko
    Mount Kosciuszko is a mountain located in the Snowy Mountains in Kosciuszko National Park. With a height of 2,228 metres above sea level, it is the highest mountain in Australia...

    ) 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 they are 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.

Range

The mountain galaxias species complex occupies a vast geographical range. They are found from southern Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...

 to the Adelaide Hills
Adelaide Hills
The Adelaide Hills are part of the Mount Lofty Ranges, east of the city of Adelaide in the state of South Australia. It is unofficially centred on the largest town in the area, Mount Barker, which has a population of around 29,000 and is also one of Australia's fastest growing towns.- History :The...

 in South Australia
South Australia
South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent; with a total land area of , it is the fourth largest of Australia's six states and two territories.South Australia shares borders with all of the mainland...

, and while occurring widely in the Murray
Murray River
The Murray River is Australia's longest river. At in length, the Murray rises in the Australian Alps, draining the western side of Australia's highest mountains and, for most of its length, meanders across Australia's inland plains, forming the border between New South Wales and Victoria as it...

-Darling
Darling River
The Darling River is the third longest river in Australia, measuring from its source in northern New South Wales to its confluence with the Murray River at Wentworth, New South Wales. Including its longest contiguous tributaries it is long, making it the longest river system in Australia.The...

 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
River capture
Stream capture, river capture, or stream piracy is a geomorphological phenomenon occurring when a stream or river drainage system or watershed is diverted from its own bed, and flows instead down the bed of a neighbouring stream...

 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 mountain galaxias species found in upland habitats, and the Flathead Galaxias
Flathead galaxias (Australia)
The flathead galaxias, Galaxias rostratus, is a freshwater fish found in lowland rivers and streams and associated billabongs, backwaters, etc of the southern Murray-Darling river system in Australia....

 found in lowland habitats. Though mountain galaxias species stray down to the upland/lowland transition zone in some river, 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, as high in fact as streams go. There has been some fascinating micro-niche partitioning amongst the Galaxiids in upland Murray-Darling habitats, this being one of the causes of the species complex we have today.

Conservation

The distribution of mountain galaxias species has been massively fragmented by the introduction of brown trout
Brown trout
The brown trout and the sea trout are fish of the same species....

 (Salmo trutta) and rainbow trout
Rainbow trout
The rainbow trout is a species of salmonid native to tributaries of the Pacific Ocean in Asia and North America. The steelhead is a sea run rainbow trout usually returning to freshwater to spawn after 2 to 3 years at sea. In other words, rainbow trout and steelhead trout are the same species....

(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. There have been countless localised extinctions of mountain galaxias species populations due to introduced trout, and this is continuing to occur with illegal trout stockings. These issues are widely recognised and documented in the scientific literature.

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

External links

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