A medium-sized catfish with a small, moderately high first dorsal fin and the classic tandan feature of conjoined caudal and anal fins. Maximum size >400 mm and 2 kg; usually less than 280 mm. The skin is smooth, with no scales. The body is slender
and the tail roundly pointed. The head and nape profile are straight and the eyes are further back along the head than in Rendahl’s tandan. The nasal barbel barely reaches beyond the eye, and the other barbels reach to the gill opening. Colour ranges from dark brown-grey to a pale yellowish brown dorsally, paling on the sides to whitish on the belly. Small specimens may be silver on the sides with yellow fins.
Breeding individuals are bright silvery-white on the sides with bright yellow fins. Individuals from very turbid waters are dull grey. Distinguished from Silver tandan which has eyes lower down on the sides of the head, and a pointed caudodorsal fin.
Apart from some knowledge on movement behaviour, very little is known of the ecology of Hyrtl’s tandan in the Basin, and the majority of the following information is drawn from studies elsewhere. The species occurs in a variety of habitats, including flowing waters or still areas such as billabongs and lagoons. Individuals may mature in their first year, (~135 mm length), but most females probably mature in their second year. Longevity is unknown, but it is thought that fish may live for up to 5 years. Sexual maturity is thought to be attained at approximately 12 months of age.
Spawning occurs during the summer wet season in northern populations and is thought to be stimulated by increasing water levels and possibly temperature. Details of the spawning site are unknown but may be in sandy areas in the upper reaches of streams.
Fecundity is little known, however, a 205 mm female had 3,630 eggs of ~1.3 mm diameter. The eggs are non-adhesive, demersal and 2.6 mm in diameter when water hardened. Hatching occurs after about 60 hours at 26–27°C.
The species appears to be tolerant of low dissolved oxygen and high turbidity, but probably not of low temperatures, with water temperatures below 8–12°C not being conducive to survival in this species. It is a nocturnal, benthic carnivore, consuming small prey items such as aquatic insects, (chironomids, caddisflies, mayflies), microcrustaceans, molluscs (small bivalves) and some detritus.
Movement patterns of Basin populations are, relatively unknown, but adults have been found moving predominantly upstream on a flow event, whilst all juveniles were captured moving downstream on the same flow. Anecdotal observations in the Paroo show that substantial numbers of adults can be found moving during the day upstream through fast water in autumn, after late summer flooding. Individuals will happily move through very shallow water (20-60 mm deep). However, in coastal Queensland it has been recorded in spring/summer moving upstream through tidal barrages, mainly at night. Upstream migration by adults to small tributary streams is presumably associated with spawning.
The species is widespread in northern and central Australia in WA, the NT and Qld, but occurs in the Murray-Darling Basin only in the north, having been recorded from the Paroo, Warrego, Culgoa, Balonne, Bogan, Barwon, Darling and Condamine rivers in northern NSW and Qld, and also the Menindee Lakes. There are occasional records from the lower Macquarie River (between Barwon and Castlereagh junctions) with the most upstream record from Warren.
A total of only 64 individuals were captured in the 9 years of the Sustainable Rivers Audit (SRA) sampling (2004–2013), with 49 from the Paroo River. The MDB Fish Survey (2014/15–2021/22) captured 3666 individuals, mostly from fyke nets (only 26 from electrofishing which was the SRA method), all from the Paroo, Condamine and Warrego catchments. Fyke net sampling in 2022 in the lower Paroo captured large numbers (thousands). Hyrtl’s tandan has been recorded to co-occur with Rendahls tandan in the Condamine catchment, but in such instances Hyrtl’s are usually at much higher abundances. It is a common species in the aquarium trade.
Evidence from both outside and inside the Basin suggests that barriers to movement may be detrimental to this species.
A catch of Hyrtl’s tandan from the Paroo River at Eulo Weir (Photo Michael Hutchison).
Allen et al. 2002; Beumer 1980; Bishop et al.
2001; Brooks et al. 2019; Brown 1992; Gehrke et al. 1999; Huey et al. 2006; Hutchison et al. 2008; Kerezsy 2020, 2022a; Larson & Martin 1989; Moffat & Voller 2002; Orr & Milward 1984; Pollard et al. 1996; Pusey et al. 2004, 2017; Stanton & Turner 2009.
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