A small, strongly laterally compressed fish reaching approximately 100 mm (but commonly <80 mm) in length. The eyes are large and positioned towards the top of the head, and the mouth is moderately large, oblique and upturned. There are two dorsal fins separated by a small gap, with the first short-based and the second long-based. There is a long-based anal fin and the tail is moderately forked. There is no lateral line.
Colouration varies with sex, age and habitat, but is generally silvery and iridescent, with a yellow and green chequered pattern on the unpaired fins and pale stripes along the sides. Unlike Murray-Darling rainbowfish, there is no pink to reddish spot on the operculum, but otherwise the two species are very similar in scale counts, number of fin rays etc. The easiest way to distinguish them is by colour. Currently, three subspecies of M. splendida are recognised, but morphological differences are slight and colour patterns are highly variable, making identification in the field difficult.
Recent genetic investigations have identified hybrids between the Desert rainbowfish and Murray-Darling rainbowfish, further confounding the identification of these species in some areas.
As its name suggests, Desert rainbowfish is an arid-adapted species, found in a variety of slow-flowing and still habitats, including ephemeral rivers, waterholes, lakes, flowing bores and stock dams. These habitats are often quite turbid and highly variable in terms of permanence.
Like other rainbowfish, the Desert rainbowfish is a schooling species and commonly seen swimming just below the water surface. Breeding is probably dependant on local conditions, occurring when water temperatures are above about 20°C and after good rains. Adults mature at about 30–35 mm length and males perform a courtship display among aquatic vegetation. The eggs are laid amongst aquatic plants or on the exposed roots of riparian vegetation (although aquatic plants and roots are not very common where this species occurs, compared to the other subspecies). In aquaria, females lay 80–100 small eggs (0.8–0.95 mm diameter), often in daily batches, and the eggs hatch after 7 days at 24°C. The newly hatched larvae are 4–5 mm long.
The species is omnivorous, consuming small aquatic invertebrates as well as filamentous algae. Although there are no dietary studies from the MDB, a study in Cooper Creek waterholes found the major dietary item in the dry season was terrestrial invertebrates (67%) with the proportion dropping to 48% and then 31% in early and late flooding respectively.
The Desert rainbowfish is widespread and abundant in the larger rivers of the Lake Eyre Basin, Bulloo Basin, and the Western Plateau of the NT. A recent genetic study has shown that the genetic makeup of Lake Eyre, Bulloo and MDB fish is quite distinct between basins, with little genetic flow between basins. Effective population size (number of fish that reproductively contribute to the next generation) was the lowest in the MDB and Finke River drainages.
Research in the Lake Eyre Basin suggests that Desert rainbowfish are capable of large dispersal movements, moving considerable distances (at least 300km) upstream into ephemeral habitats after flooding. Not bad for a small fish!
This species was only recognised relatively recently as occurring in the Murray-Darling Basin, where it is recorded from the arid rivers in the north-western Basin. It is found only in the Paroo and Warrego rivers and is the only rainbowfish that occurs in the QLD section of these rivers. Hybrids with Murray-Darling rainbowfish have been identified in the lowermost Warrego River and the Darling River from around the Bogan River down to at least Menindee. The frequency of hybrid fish in the Darling River probably changes over time as large flows from the Warrego River enhance the dispersal of Desert rainbowfish into the Darling. Any rainbowfish captured in or near the Darling River need to be carefully examined, as confusion or hybridisation with Murray-Darling rainbowfish is likely, and identification without genetic data will be difficult. A total of 1012 individuals were recorded from the Sustainable Rivers Audit (2004–2013) and 401 individuals have been captured in the MDB Fish Survey (2014/15–2021/22).
None known. Interactions with Eastern gambusia may be a threat as numbers of Desert rainbowfish at some localities appeared to decline significantly after flooding in the early 1990s facilitated the spread of gambusia. As with many rainbowfish species, introduction of other rainbowfish taxa from outside their native range can lead to hybridisation and loss of genetic integrity.
Allen et al. 2002; Attard et al. 2022a; Balcombe et al. 2005; Kerezsy 2020, 2022a; Kerezsy et al. 2013; Larson and Martin 1989; Leggett and Merrick 1987; McGuigan et al. 2000; Pusey et al. 2004; Wager and Unmack 2000; P. Unmack unpubl. data.
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