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| Melanotaenia australis [Drysdale River] - photo© Günther Schmida |
(Castelnau, 1875)
Western Rainbowfish
Description
Castelnau first described this species as Neoatherina australis in 1875. In earlier days they were commonly known as the 'Westralian Sunfish'. In 1964 another species of rainbowfish collected from the Northern Territory was named Melanotaenia solata. After Gerald Allen's review of the rainbowfish family these two species were considered as one and he placed them in the large "Splendida group" as a sub-species, and named them Melanotaenia splendida australis, but recent DNA studies indicate it is clearly distinct.
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| Melanotaenia australis [Blackmore River] - photo© Günther Schmida |
Their colouration, particularly the fins and intensity of the mid-lateral stripe, is highly variable depending on their geographic locality. This is mainly due to a rapid speciation in the rainbowfish group and is further enhanced by the degree of random morphological variation occurring among the various populations. Fins range from nearly colourless to deep red, or clear with red or green flecks. Gerry Allen notes that the real trademark of this species is the zigzagging blackish lines on the lower sides, just above the anal fins. The black mid-lateral line may be very prominent or scarcely apparent. Fish from the Drysdale River of Western Australia are generally smaller in statue and possess a distinctive double mid-lateral black stripe.
Distribution
The original type specimens (23) were collected from Weeli Wolli, Hammersley Range, and Millstream homestead in Western Australia. Melanotaenia australis occurs in river systems of north-western Australia; the Ashburton River forms the western and southern limit of its distribution. It is common in most streams of the Kimberley region and the north-western Northern Territory from the Fitzroy River to the Adelaide River, just east of Darwin.
Habitat & Ecology
A stream dwelling rainbowfish mainly found around sub-surface vegetation, submerged logs, or branches in small tributary streams, but can also occur in swamps and lagoons. Their natural environment is subjected to seasonal variations with water temperature, pH, and hardness levels varying considerably. There is often a large fluctuation in water conditions between the dry and wet seasons.
Males are easily distinguished from females by their brighter colours and longer and more elongated dorsal fin rays. Growing to a length of around 10 to 12 cm, males are usually much larger and deeper bodied than females. Spawning occurs from October to December, with females producing between 100 and 200 eggs. Eggs adhere to water plants and hatching occurs around 6 to 10 days. Growth is rapid reaching 2-3 cm in 10 to 12 weeks.
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| Melanotaenia australis [Carrawine Gorge] - photo© Neil Armstrong |
Remarks
Melanotaenia australis is highly variable in colour across its range. Recent genetic research provides support for the separation of Melanotaenia australis into two species: a southern one from the Pilbara area and the remaining northern populations. Pilbara populations are quite distinct and lack the mid lateral band that is prominent in many other Melanotaenia australis populations.
© Copyright Adrian R. Tappin
Updated January, 2007.
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