Eastern Dwarf Galaxias, Galaxiella pusilla (Mack 1936)
A Eastern Dwarf Galaxias, Galaxiella pusilla, from the Dandenong area. Source: John McGuckin. License: All rights reserved
A very small pale olive-brown galaxiid with a silvery-white belly, three faint dark stripes along the side, and a distinct v-shaped black mark often on the isthmus (fleshy area on the underside between the gill chambers), usually extending to near the pelvic-fin bases as two parallel dotted lines. Males have a bright orange mid-lateral stripe. Juveniles lack the distinct striped patterns and colour of adults, are predominantly pale olive to beige above, silvery-white below.
Populations have been dramatically affected by human induced changes such as the draining of swamps, and the species is now protected throughout its range.
Eastern Dwarf Galaxias, Galaxiella pusilla (Mack 1936)
More Info
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Distribution |
Endemic to temperate freshwaters of coastal southeastern Australia, including Tasmania, from the Mitchell River Basin near Bairnsdale in eastern Victoria, westwards to south-east Melbourne, and Flinders Island in Bass Strait, and north-eastern and north-western Tasmania. The species has a patchy and disjunct distribution, and may have become extinct in some Victorian and Tasmanian localities. The Eastern Dwarf Galaxias inhabits both ephemeral and permanent still or gently flowing waters of roadside ditches, swamps and creek backwaters, usually with abundant submerged and emergent aquatic vegetation. Although typically preferring swampy floodplain habitats, they also occur in creeks and streams. |
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Features |
Dorsal fin 6-9 (usually 7-8); Anal fin 8-11 (usually 8-10); Pectoral fin 10-14 (usually 11-13); Pelvic fin 4-6 (usually 4-5); Gill rakers (first arch) 12-17 (usually 14-16). Body elongate, stout, deeper at belly; body depth at vent 5.4-7.2 in SL; head small; snout short, blunt; jaws equal; sensory pores under lower jaw absent; Scales absent. Caudal peduncle (tail base) with a low membranous fold almost to dorsal- and anal-fin rays; dorsal-fin small, originating far back on body behind level of anal fin; caudal fin rounded; pelvic fins small. |
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Size |
Maximum length about 4 cm, commonly to 3.5 cm; females grow larger than males. |
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Colour |
Adults are sexually dimorphic in colour. Both sexes are overall brownish-green to greenish-orange above, silvery white below with transparent fins. Males have three black stripes along each side with a bright orange stripe between the two lower black stripes. Females may have a golden midlateral stripe, and the black stripes are indistinct or absent. |
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Feeding |
Feeds on small insects, aquatic insect larvae, zooplankton including microcrustaceans, and some algae. |
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Biology |
Eastern Dwarf Galaxias complete their entire lifecycle in freshwater. Although they may spawn year-round in favourable conditions, most spawning occurs during late winter to October. Females deposit a few small adhesive eggs (to 1.3 mm diameter) daily onto leaf litter and dense aquatic vegetation. The larvae hatch after 10-17 days at temperatures of 16-21°C. The species is short-lived, with individuals reaching reproductive maturity in their first year and dying soon after spawning. |
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Conservation |
Although locally abundant in some areas, the Eastern Dwarf Galaxias has a patchy distribution, and populations have been severely affected by human habitation, especially the draining of swamps and alterations to waterways. The species is also threatened by the spread of the introduced and invasive Eastern Gambusia, Gambusia holbrooki. Climate change is expected to have increasing impacts on Eastern Dwarf Galaxias habitats. |
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Remarks |
Eastern Dwarf Galaxias appear to be adapted to survive for more than a week without surface water by finding refuge in burrows or amongst wet aquatic vegetation and detritus (Coleman et al. 2016). |
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Similar Species |
Galaxiella pusilla differs from Galaxiella toourtkoourt in having a combination of the following characters: more vertebrae; a slightly longer caudal peduncle; more pronounced dorsal fin-anal fin setback, especially in females; and, adults are larger. |
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Species Citation |
Galaxias pusillus Mack, 1936, Mem. Natl. Mus. Vict. 9: 101. Type locality: Cardinia Creek, Victoria. |
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Author |
Bray, D.J. 2020 |
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Resources |
Eastern Dwarf Galaxias, Galaxiella pusilla (Mack 1936)
References
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Allen, G.R. 1989 Freshwater fishes of Australia. T.F.H. Publications, Inc., Neptune City, New Jersey.
Allen, G.R., Midgley, S.H. & Allen, M. 2002. Field Guide to the Freshwater Fishes of Australia. Perth : Western Australian Museum 394 pp.
Backhouse, G.N. & Vanner, R.W. 1978. Observations on the biology of the dwarf galaxiid, Galaxiella pusilla (Mack) (Pisces: Galaxiidae). Victorian Naturalist 95: 128-132
Berra, T.M. & Allen, G.R. 1989. Clarification of the difference between Galaxiella nigrostriata (Shipway, 1953) and Galaxiella munda McDowall, 1978 (Pisces: Galaxiidae) from Western Australia. Records of the Western Australian Museum 14: 293-297 See ref online
Brown, T.R., Todd, C.R., Hale, R., Swearer, S.E. & Coleman, R.A. 2020. Testing the adaptive advantage of a threatened species over an invasive species using a stochastic population model. Journal of Environmental Management 264, https://doi.org/10.1016/j.jenvman.2020.110524
Cadwallader, P.L. & Backhouse, G.N. 1983. A Guide to the Freshwater Fish of Victoria. Melbourne : F.D. Atkinson Government Printer 249 pp. figs.
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Coleman, R.A. 2014. Conservation of the dwarf galaxias, Galaxiella pusilla (Mack 1936) (Teleostei: Galaxiidae), a threatened freshwater fish from south-eastern Australia. PhD Thesis, University of Melbourne, Parkville, 262 pp.
Coleman R.A. & Hoffmann A.A. 2016. Digenean trematode cysts within the heads of threatened Galaxiella species (Teleostei : Galaxiidae) from south-eastern Australia. Australian Journal of Zoology 64: 285-291. https://doi.org/10.1071/ZO16004
Coleman, R.A., Hoffman, A.A. & Raadik, T.A. 2015. A review of Galaxiella pusilla (Mack) (Teleostei: Galaxiidae) in south-eastern Australia with a description of a new species. Zootaxa 4021(2): 243-281.
Coleman, R.A., Pettigrove, V., Raadik, T.A., Hoffmann, A.A., Miller, A.D. & Carew, M.E. 2010. Microsatellite markers and mtDNA data indicate two distinct groups in dwarf galaxias, Galaxiella pusilla (Mack) (Pisces: Galaxiidae), a threatened freshwater fish from south-eastern Australia. Conservation Genetics 11: 1911–1928
Coleman, R.A., Raadik, T.A., Pettigrove, V. & Hoffmann, A.A. 2017. Taking advantage of adaptations when managing threatened species within variable environments: the case of the dwarf galaxias, Galaxiella pusilla (Teleostei, Galaxiidae). Marine and Freshwater Research 68(1): 175-186 http://www.publish.csiro.au/mf/MF15332
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