Riffle Galaxias, Galaxias arcanus Raadik 2014

A Riffle Galaxias, Galaxias arcanus, photographed in an aquarium. Source: Tarmo A. Raadik / Arthur Rylah Institute. License: All rights reserved

A small Galaxias with a very short lower jaw overhung by a 'bulbous' upper lip, relatively flat dorsal and ventral profiles, a long slender tapering caudal peduncle, large ventrally-oriented pectoral fins, a very high dorsal fin, and the anal fin originating behind a vertical from the dorsal-fin origin.

Cite this page as:
Bray, D.J. 2021, Galaxias arcanus in Fishes of Australia, accessed 16 Apr 2024, https://fishesofaustralia.net.au/home/species/5121

Riffle Galaxias, Galaxias arcanus Raadik 2014

More Info


Restricted to cooler and faster-flowing upland reaches within a band on the north of the Great Dividing Range in north-eastern Victoria, including the upper Murray River from near the headwaters and extending westward to the Acheron River, Goulburn River system, at an elevation of between 150–880 m. 
Inhabits cold to relatively cool, clear water in flowing creeks to large rivers, usually in shallow, fast-flowing and high energy riffles and runs, although juveniles have been recorded moving upstream through slow water along the shallow edges of pools. Riffle Galaxias usually occur among or under rocks on the stream bed, or deeper in the interstitial spaces of the substrate comprised mostly of abundant cobbles and pebbles, with smaller amounts of bedrock, boulder, gravel and coarse sand.


A distinctive member of the Galaxias olidus complex that differs from all others in having the following combination of characters: shallow body with a straight ventral profile; long and shallow caudal peduncle, the peduncle length greater than the caudal fin length; caudal peduncle flanges poorly developed; a distinctive snout which extends anteriorly from the thick and fleshy upper jaw as a fleshy protrubence, bulbous in lateral profile; nostrils of moderate length, usually not visible from ventral view; subterminal mouth and lower jaw 82 % of length of upper jaw; most anterior tip of snout level with about lower 0.3 of eye diameter; head wide and shallow; short PrePel, PecPel and PoHL dimensions; large, ventrally oriented pectoral and pelvic fins (14.4 and 11.8 % SL respectively); low mean vertebral count of 51, though range broad (47–55); 0–1 pyloric caecae, short (1.0 % SL) and wide when present; gill rakers of moderate length, thin and sharply pointed; anal fin origin usually under 0.4 distance posteriorly along dorsal fin base; distinctive cryptic colouration; and, lack of black bars along lateral line.


To at least 7.5 cm SL


Predatory Rainbow Trout (Oncorhynchus mykiss) occur in the same habitats as the Riffle Galaxias, which presumably avoid predation by occupying high energy riffle habitats which may be marginal for trout, and also by their cryptic colouration, and ability to remain hidden amongst habitat on or within the stream bed (Raadik 2011). 
Sowersby et al. (2016) found that Riffe Galaxias avoided trout when only sand substrate was available, but did not avoid trout when cobble substrate was available, suggesting that the complex structure of cobbles may afford Riffle Galaxias protection from trout.


The specific name is from the Latin arcanus (= cryptic, secret, mysterious) in reference to the cryptic habitat occupied by this species (amongst boulder and cobbles on the stream bed), and its cryptic coloration. 

Species Citation

Galaxias arcanus Raadik 2014, Zootaxa 3898(1): 37, figs 8 -11. Type locality: Wheelers Creek, just upstream of bridge on Wheelers Creek Logging Road and junction with Zulu Creek, upstream of O’Hagens Campsite, south of Staceys Bridge, Victoria [36°32'23”S, 147°49'44”E]. 


Bray, D.J. 2021


Atlas of Living Australia

Riffle Galaxias, Galaxias arcanus Raadik 2014


Adams, M., Raadik, T.A., Burridge, C.P. & Georges, A. 2014. Global biodiversity assessment and hyper-cryptic species complexes: more than one species of elephant in the room. Systematic Biology 63(4): 518–533 https://doi.org/10.1093/sysbio/syu017 (as taxon 'RF')

Gilligan, D., Rodgers, M., McGarry, T., Asmus, M. & Pearce, L. 2010. The distribution and abundance of two endangered fish species in the NSW upper Murray catchment. Industry and Investment NSW, Fisheries Final Report Series No. 127. 34 pp. (as Galaxias sp. 2)

Koehn, J. 2002. Fish of the Murray River. Victorian Naturalist 119(4): 152–159 (as Galaxias olidus in part)

Kuiter, R.H. 2013. Pictorial Guide to Victoria's Freshwater Fishes. Seaford, Victoria : Aquatic Photographics 178 pp. (as Galaxias sp. 3)

Lieschke, J.A., Dodd, L., Stoessel, D., Raadik, T.A., Steelcable, A., Kitchingman, A. & Ramsey, D. 2013. The status of fish populations in Victorian rivers 2004–2011—Part A. Arthur Rylah Institute for Environmental Research Technical Report Series 246, Department of Sustainability and Environment, Heidelberg, Victoria. 148 pp. (as Galaxias sp. 2)

Lieschke, J.A., Dodd, L., Stoessel, D., Raadik, T.A., Steelcable, A., Kitchingman, A. & Ramsey, D. 2013. The status of fish populations in Victorian rivers 2004–2011—Part B: Individual basin assessments. Arthur Rylah Institute for Environmental Research Technical Report Series 247, Department of Sustainability and Environment, Heidelberg, Victoria. 353 pp. (as Galaxias sp. 2)

Lintermans, M. 2007. Fishes of the Murray-Darling Basin — An Introductory Guide. Canberra : Murray-Darling Basin Commission Vol. MDBC Publication Number 10/07 157 pp. (as Galaxias olidus, in part)

Raadik, T. 2001. When is a mountain galaxias not a mountain galaxias? Fishes of Sahul, Journal of the Australian New Guinea Fishes Association 15(4): 785-789 (as Galaxias sp. nov, in part)

Raadik, T.A. 2011. Systematic revision of the Mountain Galaxias, Galaxias olidus Günther, 1866 species complex (Teleostei: Galaxiidae) in eastern Australia. Ph.D thesis, University of Canberra. pp. i-xxiii, 1-493 (as taxon 'riffle')

Raadik, T.A. 2014. Fifteen from one: a revision of the Galaxias olidus Günther, 1866 complex (Teleostei, Galaxiidae) in south-eastern Australia recognises three previously described taxa and describes 12 new species. Zootaxa 3898(1): 1-198 https://doi.org/10.11646/zootaxa.3898.1.1

Raadik, T. 2019. Galaxias arcanus . The IUCN Red List of Threatened Species 2019: e.T122902237A123382101. https://dx.doi.org/10.2305/IUCN.UK.2019-3.RLTS.T122902237A123382101.en. Downloaded on 05 February 2020.

Sowersby, W., Thompson, R. & Wong, B. 2016. Invasive predator influences habitat preferences in a freshwater fish. Environmental Biology of Fishes 99(2-3): 187-193. https://doi.org/10.1007/s10641-015-0466-5

Quick Facts

CAAB Code:37102025

Conservation:IUCN Least Concern


Max Size:7.5 cm SL


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