A small, fish with a truncate to rounded tail. Maximum length 65 mm total length (TL); rarely more than 40 mm. The head is broad and flat with a large mouth and well-separated eyes (when viewed from above). Males have a larger mouth, extending beyond the rear margin of the eye, whereas in females it extends to below the middle of the eye. The gill openings on the underside of the head are narrow, extending forward to below the posterior portion of the gill covers, ending well behind the eye. It has two separate dorsal fins.
The upper head and body is brown to black with irregular blotches, and a vertical black bar on the base of the caudal fin. Two black oblique bands extend backwards from the eye. The first dorsal fin has two black bands interspersed with orange or whitish areas. The second dorsal fin has 3–4 black stripes, also interspersed with orange or whitish areas. The caudal fin has orange spotting. Can be distinguished from small individuals of Flat-headed gudgeon which has narrower gill openings which do not extend to, or below the eye; eyes close together; fewer pectoral fin rays (15–16); and lacks the black bar at the base of the tail.
Dwarf flat-headed gudgeon has been confused with Flat-headed gudgeon in the literature and some references to Flat-headed gudgeon prior to 1980 probably refer to Dwarf flat-headed gudgeon. The two species are sympatric throughout most of their range. Dwarf flat-headed gudgeon is often considered to exhibit more specialised habitat preferences than Flat-headed gudgeon, being predominantly found in off-channel wetlands and small anabranches and streams, where it is found in relatively calm waters and over mud and rock substrates or in weedy areas. They can often be captured in or around Willow tree roots. However, recent information from coastal populations in south-eastern Queensland indicates that this species occurs over coarser substrates such as gravel and cobbles, close to submerged cover such as leaf-litter accumulations, woody habitat and aquatic vegetation.
Nothing is known of the reproductive biology in the wild, and little is known of its general ecology in the Basin. This species likely reaches maturity by one year. In aquaria it has been recorded breeding at temperatures of 19–22°C. The eggs are transparent and teardrop shaped, and hatch in 4–5 days. The male fish guards the egg mass, fanning them regularly and driving away other fish. The Dwarf flat-headed gudgeon is a benthic carnivore, feeding mainly on aquatic insects and their larvae such as chironomids, mayflies and caddisflies.
Dwarf flat-headed gudgeon is relatively common in coastal streams from southern Qld to Wilsons Promontory in Vic, and there are some outlying coastal populations near Adelaide in eastern SA. They occur also in the inland MDB but are patchily distributed and have only been recorded from relatively few localities. It is most commonly recorded in the mid and lower Murray River and tributaries such as Gunbower Creek at or downstream of Cohuna/Swan Hill, but occasional individuals are recorded up to below Yarrawonga Weir. Previously found around Albury in the 1970s and early 1990s, but efforts to relocate any have failed.
Historically it was known from the Macquarie drainage near Bathurst in the 1800s, and more recently from the Cudegong River, the Murrumbidgee near Canberra, and in the lower Darling River near Wentworth in NSW. In Qld it is known from the Condamine primarily between Condamine and Chinchilla, the Balonne River at Dirranbandi, and the Macintyre River. In Vic there are records from the lower Goulburn River, Broken River, Cardross Lakes and Serpentine Weir on the Loddon River. In SA it is recorded from the wetlands and main channel of the Lower Murray and Lower Lakes, and the Mount Lofty Ranges.
In the Sustainable Rivers Audit from 2004–2013 it was the fourth-rarest native species captured, with a total of only 9 individuals collected (compared to Flat-headed Gudgeon: 2197 recorded), with 6 from the Lower Murray, 2 from the Loddon and 1 from the Murrumbidgee. 37 were recorded in the MDB Fish Survey (2014/15–2021/22) from 2 valleys (32 from Murrumbidgee and 5 from Lower Murray). In wetland or off-channel habitats in the Lower Murray in South Australia it is widely distributed, but generally captured in low abundance. The species has not been recorded from the ACT.
None known. Predation (larval and adult) by alien fishes and interaction with the aggressive Eastern gambusia may be threats.
Allen et al. 2002; Bloink & Halliday 2021; Fletcher 1997; Hammer 2004; Higham et al. 2005; Hoese & Reader 2006; Hutchison et al. 2008; Koehn & O’Connor 1990; Larson & Hoese 1996a; Lintermans & Osborne 2002; Lloyd & Walker 1986; Merrick & Schmida 1984; Pusey et al. 2004; Scott et al. 2019; Shoesmith 2015; Smith et al. 2009; Thacker et al. 2008; Wedderburn et al. 2014.
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