A small, slender fish with a slender caudal peduncle. Maximum size 190 mm; usually <100 mm. Scales are absent, the tail is slightly forked, and the anal fin originates directly below the dorsal fin. The head is small and bluntly pointed and the mouth is small, only reaching back to the front of the eyes. The jaws are equal in length.
Overall translucent grey-olive to amber in colour, with the back and sides irregularly blotched or spotted greenish grey. The belly, eyes and gill covers are bright silvery to white. The fins are largely translucent.
This schooling species is commonly found in coastal habitats, in still or slow-flowing streams and the margins of lagoons and lakes. It is a diadromous (catadromous) species with coastal stream populations exhibiting adult downstream migrations to brackish areas and spawning in autumn–spring.
Eggs are spawned on terrestrial vegetation on spring tides, either in flooded shallow margins of streams or above the normal tideline in estuaries. The adhesive eggs (~ 1 mm diameter) develop largely ‘out of water’ over about 14 days and hatching is stimulated by the next high tide or flood. Eggs are able to survive without immersion for up to 8 weeks.
Precise spawning cues are unknown, but in Australia are likely to include day length and water temperature, as shorter day lengths and cooler temperatures are more likely to reduce the risk of desiccation of the exposed eggs. In a coastal Vic river, downstream adult movements to spawn were rapid (typically 1–3 days), up to 50 km, and occurred after increased river discharge, and when the moon was becoming brighter.
Spawning schools have a male-biased sex ratio, even late in the spawning season, suggesting that males may spawn more than once per season.
The larvae disperse to sea for an average of 90–125 days before returning to streams the following spring as unpigmented juveniles (<50 mm) known as ‘whitebait’. The pelagic larval period is longer in spring than it is in summer, with late season fish returning earlier. Spawning in the Lower lakes and Coorong, in South Australia, may be protracted from June to November, but peak spawning typically occurs from June to August. Peak juvenile upstream migration occurs from late September to early December.
The species can also occur as landlocked populations in lakes, where breeding occurs in late winter-early spring on rising water levels, with adults making a short migration into tributaries to spawn. The larvae are washed down into lakes to spend several months amongst the shallow shoreline vegetation. Individuals are mature at the end of their first year, (~ 90 mm length), although some do not breed until their second year. Very few survive until the end of their third year and a substantial proportion of adult fish die after spawning. Each female produces several thousand eggs (up to 13,500).
The species is carnivorous and takes food from the bottom, mid-water or the surface. The diet of landlocked populations consists mainly of amphipods, chironomid larvae and microcrustaceans; stream-dwelling individuals consume more insects. In coastal populations in Vic, elevated flows increase the abundance of juveniles returning from marine environments.
The Common galaxias has one of the world’s most naturally widespread distributions for a freshwater fish, occurring in southeastern and southwestern Australia, Lord Howe Island, New Zealand and South America including Chile, Argentina and Falkland Islands. In Australia it is a common fish of lowland coastal streams, from SA to southern Qld and Tas. In the Murray-Darling Basin it is known from the Lower Lakes (Alexandrina and Albert), extending up to approximately Mannum on the Lower Murray and streams of the Mt Lofty Ranges in SA. Its abundance in the lower Basin is influenced by operation of the barrages between the Lower Lakes and Coorong, which may act as a barrier to downstream spawning migrations and upstream whitebait migrations.
During a prolonged period of barrage closure from 2007 to 2010 towards the end of the Millennium Drought, abundances of upstream migrants decreased by >90%. There was, however, some evidence of reproduction within freshwater habitats in the Lower Lakes over this period. Nevertheless, this population appears to be predominantly diadromous and fishways on the barrages now facilitate the annual upstream migration of thousands of individuals.
It is also known from the Wimmera, Loddon, and Campaspe catchments in Vic, where it is considered a translocated species, probably introduced through water diversions from coastal streams or in bait-buckets. The species has recently been recorded from Dartmouth Dam where it is probably the result of bait-bucket introductions by anglers.
A total of 131 individuals were collected in the Sustainable Rivers Audit (2004–2013), with the majority (98) coming from the Wimmera River in Vic. 21 individuals have been collected in the MDB Fish Survey (2014/15–2021/22) across the Lower Murray, Mitta Mitta and Wimmera catchments.
Barriers to movement impede both downstream adult spawning migrations, and upstream whitebait migrations. Reduced flows may be reducing spawning opportunities for landlocked recruitment and migration.
Allen et al. 2002; Amstaetter et al. 2021; Barbee et al. 2011; Becker et al. 2005; Bice et al. 2012, 2016a, 2017, 2019b; Chapman et al. 2006; Koster et al. 2023; McDowall & Fulton 1996; Pollard 1971, 1972, 1973; Zampatti et al. 2010.
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