A small to medium sized, laterally compressed fish with a relatively slender body for a grunter. Maximum size 330 mm; rarely 250 mm and 560 g; commonly 150 mm. The single dorsal fin has a moderately-sized notch between the spinous and soft-rayed portions. The pelvic fins are inserted behind the origin of the pectoral fins. The anal and pelvic fins are white. The back is generally brown to steely-blue and the sides silvery-grey with numerous bronze to rusty-brown spots. The tail is slightly forked, the eye is small to moderate, and the mouth is of moderate size with equal jaws.
The Spangled perch is a hardy species that is well adapted to surviving in diverse environments including rivers, billabongs, lakes, isolated dams, bore-drains, wells and waterholes in intermittent streams. It can survive temperatures up to 40°C, but is relatively intolerant of colder water with a lower lethal limit of around 4.1°C and reduced survival below 7.2°C. It is tolerant of warm water and has exceptional dispersal abilities.
Often reported in ‘rains of fishes’ it is likely to have quickly swum through overland surface waters (sometimes just centimetres deep) following heavy rainfall, rather than having fallen from the sky (check the house gutters/water tank). This allows it to rapidly colonise habitats not readily accessible to other fish species. It has been observed swimming across flooded paddocks and along wheel ruts on tracks for up to 16 km.
Individuals mature in their first year, males at about 58 mm length and females at 78 mm. Breeding occurs from November to February and fecundity is high and size-dependant, with between 24,000 and 113,200 eggs per female. Spawning occurs at night, in shallow areas such as backwaters or still pools, when water temperatures are above 20–22°C and with eggs spread randomly over the sediments. The eggs are small (0.7 mm diam.), round, demersal, non-adhesive and hatch in 45–55 hrs at 23–26°C. Although a rise in water level is not essential (the species will breed in impoundments), flooding enhances recruitment by facilitating dispersal. Movement can be associated with spawning or dispersal, and fish move rapidly upstream, downstream, or laterally in flooded environments.
Spangled perch is primarily a carnivore eating aquatic insects, shrimps, microcrustaceans and fish, although it also consumes some plant material (~10 % of diet). It feeds mainly during daylight hours. As a member of the Grunter family, Spangled perch emit a distinctive, species-specific ‘grunt’ which can be readily detected. The sound is produced by vibrating its swim bladder, with the purpose of the grunt unclear (but is potentially related to mate choice, territoriality, or recognising the identity of competitors).
The Spangled perch is Australia’s most widespread native freshwater fish, occurring across most of northern Australia. In the Murray-Darling Basin it commonly occurs throughout the Darling catchment except in the colder higher elevations such as the upper Macquarie River. It was the 5th most abundant species (5423 individuals) caught in the Sustainable Rivers Audit (2004–2013) (3.6% of the total fish catch) with 79% of these coming from lowland (0–200 m elevation) sites.
Similarly, of the 1306 individuals recorded by the MDB Fish Survey (2014/15–2021/22) 76% were captured in lowland sites, with the southernmost river valley where recorded being the Macquarie. Vagrants have occasionally been recorded in the Murray River system after extensive flooding in the northern Darling Catchment. Following widespread flooding in the Basin in 2010 and 2011, more than 1300 occurrences of this species were reported in the Darling River downstream of Menindee and the lower Murray River (downstream of Euston). Low abundances persisted in the lower Murray system over 2–3 years, and evidence of in situ recruitment was detected in several southern MDB locations.
However, the species has not persisted in the southern MDB with no records from the Murray in Sustainable Rivers Audit after 2011 and none in the MDB Fish Survey (2014/15–2021/22). Some individuals were still present in the mid and lower reaches of the Great Darling Anabranch in early 2014. The lack of persistence is a result of cold winter water temperatures which lead to stress-related disease in this species. The species is not known from the ACT or Vic beyond environments directly associated with the lower Murray River. Spangled perch can be very abundant, especially after flooding, although this varies with seasonal conditions.
Spangled perch has lower abundance in regulated rivers, with aspects such as cold-water pollution, barriers to fish movement, reduced flooding, and access to floodplains likely to disadvantage it.
Allen et al. 2002; Beumer 1979b, c; Bishop et al. 2001; Bostock et al. 2006; Ellis et al. 2015; Harris & Gehrke 1997; Kerezsy 2020, 2022a; Linke et al. 2018; Llewellyn 1973; Medeiros 2004; Merrick 1996; Merrick & Schmida 1984; Pusey et al. 2004, 2017.
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