A small, laterally compressed fish with a deeply notched single dorsal fin. Maximum size 85 mm; usually <65 mm. The tail is squarish to slightly rounded, and the mouth is small, reaching to just below the front of the eye. The lower edge of the preorbital bone is hidden under skin and is curved with a smooth (non-serrate) edge (compare with Yarra pygmy perch). The pupil is round, (compared with irregular in Yarra pygmy perch). The lateral line is discontinuous.
Body colour varies from cream to gold-orange to a greenish-brown, darker on the dorsal surface, and almost white on the belly, with a series of dark blotches on the side. Breeding males have bright red dorsal, anal and inner caudal fins, and also have prominent black colouration on the pelvic and anal fins and around the vent.
The Southern pygmy perch prefers slow flowing or still waters, usually with dense aquatic vegetation and plenty of cover. It has been recorded from small streams, well-vegetated lakes (or wetlands within), billabongs and irrigation channels. Fish can live for 5 years or more although most individuals in a population are <3 years old. It can tolerate a broad range of temperatures and extremely low dissolved oxygen levels.
Females grow larger than males and both sexes mature in their first year at 30–33 mm. Spawning usually occurs September to January when water temperatures exceed 16°C, and males are territorial when breeding. Depending on their size, females produce 100–4,200 round, transparent and non-adhesive eggs. The eggs are scattered over the bottom or aquatic vegetation and hatch in 2–4 days, with the larvae about 3–4 mm long.
The species is carnivorous, eating cladocerans, copepods, ostracods, and small insect larvae such as chironomids, mayflies, mosquito larvae and water bugs. Southern pygmy perch has relatively poor dispersal abilities, with sustained swimming speed and endurance capacities substantially lower than other small fish species such as Mountain galaxias. Research in creeks and wetlands of the Barmah-Millewa Forest demonstrated that recruitment and dispersal of this species significantly increased during the 2005 environmental water release that inundated the floodplain compared to non-flood years.
Formerly found in the lower Murrumbidgee and Murray and catchments, and relatively recently discovered in the Lachlan catchment, the Southern pygmy perch has now disappeared from most locations in NSW with extant populations only known from 3 catchments; the upper Lachlan drainage near Dalton (Blakney, Urumwalla, Oolong creeks); upper Billabong Creek near Holbrook; and Coppabella Creek near Albury.
A translocated population has been established in Pudman Creek (Boorowa River) NSW. In the 1950s J.O. Langtry recorded that pygmy perch, “appear to abound throughout the whole Murray system”. Sadly, this is no longer true. The species is still present in the Mount Lofty Ranges and the Lower Lakes in SA, where it is highly threatened. The species was effectively extirpated from the Lower Lakes during the Millennium Drought as salinity levels rose and fringing reedbed habitats dried. The species was rescued from drying habitats, and ultimately reintroduced following captive breeding and maintenance following the 2010 ending of the drought. After just ticking along following reintroduction, the population in the Lower Lakes has dramatically improved in 2022.
It is patchily distributed along Vic tributaries of the Murray, where it is still known from the Broken, Ovens, Campaspe, Goulburn, Kiewa, Mitta Mitta, Loddon and Wimmera basins. Consecutive drought years and subsequent flooding during the Millennium Drought resulted in local extirpations in Barmah/Millewa, Normans Lagoon, Happy Valley Creek, Tallangatta Creek, Khancoban Lagoon and probably the lower Ovens floodplain. It is still relatively common in southern coastal Vic, southeast SA and northern Tas. Recent genetic studies have shown there are two species within the Southern pygmy perch: an eastern coastal species and a species in the Basin and western coastal streams. The Basin form likely represents a separate evolutionarily significant unit (lineage) and is now no longer widespread and is rarely abundant in any location following severe declines and population fragmentation since the 1970s.
In Victoria Southern pygmy perch have been released at >20 farm dams in the Loddon catchment plus wetlands, dams and successful surrogate sites in Tahbilk Lagoon and North Central CMA, with releases also into the Murray, upper Lachlan, and Edward catchments in NSW. 1660 individuals were recorded from the Sustainable Rivers Audit (2004–2013), from 10 river valleys (70% and 30% from slopes and lowland elevational zones respectively). 366 have been recorded in the MDB Fish Survey (2014/15–2021/22) from 4 river valleys.
Predation by alien species such as trout, Redfin perch and possibly Eastern gambusia, and possible interactions with Carp are likely to have played significant roles in the decline of this species. For example, Redfin perch is actively invading Blakney Creek in NSW with the distribution of pygmy perch in this stream shrinking by >50% in recent years as Redfin invade. Habitat alteration such as loss of aquatic vegetation, floodplain alienation, cold-water pollution, water abstraction and seasonal flow changes/reductions are also likely to be involved.
Prolonged drought leading to isolation and /or desiccation of habitats, and subsequent flooding and blackwater events can have severe impacts on small, localised populations, with rescues conducted for this species in Coppabella Creek and the Lower Lakes and Mt Lofty Ranges during the Millennium Drought and then Urumwalla and Coppabella creeks in the 2019 drought in NSW. In contrast, flood events can also scour away reedbeds, destroying important refuge habitat and exposing pygmy perch to increased predation.
Attard et al. 2016a; Cook et al. 2007; Dexter et al. 2014; Hammer 2002a; Hammer et al. 2013; Higham et al. 2005; Humphries 1995; Koehn et al. 2020a; Kuiter et al. 1996; Lintermans & Pearce 2017; Lintermans et al. 2022; Llewellyn 1974, 1980; Lloyd & Walker 1986; McNeil & Closs 2007; Pearce 2014, 2015; Pearce et al. 2019; Tonkin et al. 2008; TSSC 2020; Unmack et al. 2011; Wedderburn et al. 2014; Whiterod et al. 2019; Woodward & Malone 2002; Zukowski et al. 2021.
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