| Ornate rainbowfish | |
|---|---|
 | |
| Male from Searys Creek, southeast Queensland, Australia | |
 | |
| Female from Searys Creek, southeast Queensland, Australia | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Atheriniformes |
| Suborder: | Atherinoidei |
| Family: | Melanotaeniidae |
| Genus: | Rhadinocentrus Regan, 1914[2] |
| Species: | R. ornatus |
| Binomial name | |
| Rhadinocentrus ornatus Regan, 1914 | |
Theornate rainbowfish (Rhadinocentrus ornatus) is a species ofrainbowfishendemic to an area in easternAustralia, where it is native to coastal regions and sandy offshore islands in southernQueensland and northernNew South Wales. It is the only known member of itsgenus. It is a popular aquarium fish.
The ornate rainbowfish is a small, slender and rather elongated species of rainbowfish. It has twodorsal fins that are only narrowly separated, and the first dorsal fin is considerably smaller than the second.[3] There are 3 to 5 thin, soft spines in the first dorsal fin while the second dorsal fin has 11–15 segmented rays.[4]
This species is highly variable in colour over its range. The body is semi-transparent, and they have two rows of black scales along the middle of their flanks. They haveiridescent scales above thelateral line and just below the dorsal fin, and these can be either red or a metallic light blue. The dorsal,anal andcaudal fins are normally blue, although are sometimes red, and have black edges.[3] The semi-transparent body may have hues of blue, pink or red with the dark edges of the scales creating a network-like pattern and the two mid-lateral dark stripes described above. They have neon blue iridescent patches on their backs and on the nape. An example of the geographic variation in colour is that a golden-yellow morph is found in the Key Hole Lakes system onStradbroke Island,[4] while another population on that island had distinctive black stripes on the flanks which created an overall dark colouration.[3] The males of this species grows to a length of 6 centimetres (2.4 in)Standard Length, the females to 3.5 centimetres (1.4 in).[5]
The ornate rainbowfish is found in subtropical freshwaters in southern Queensland and northern New South Wales. Its range is coastal areas to the east of theGreat Dividing Range from nearMaryborough toCoffs Harbour. The species distribution extends to sandy islands of southern Queensland includingBribie,Fraser,Moreton andNorth Stradbroke Islands.[3][4] On the mainland its distribution is continuous in the southern part of its range but there is a disjunct population in theByfield area which is separated from the southern population by 350 kilometres (220 miles).[3]
Ornate rainbowfish inhabit freshwater creeks, streams, ponds and dune lakes in the coastal dune habitat locally known aswallum. Their typical habitat is sandy coastal areas where they are found in sluggish, acid waters stained withtannins from vegetation falling into the water where there is woody debris in the water, grassy banks, and thick submerged and emergent vegetation.[4] In these habitats the ornate rainbowfish prefers to be in cover among submerged woody debris, in grassy banks and reeds; and withinwaterlily roots.[5] It has also been recorded in clear streams with a slow current and little or no vegetation ingallery forests.[4] This species can tolerate very soft waters and is known to live in water as acidic as orange juice.[6]
This species congregates in small schools, especially where the habitat is clear, slow, shady streams over sands. These may be mixed schools withNannoperca oxleyana andPseudomugil mellis.[3] Thisomnivorous species feeds mainly from the surface, and its diet consists of crustaceans, aquatic and terrestrial insects, pollen, algae and organic detritus.[4] It issexually dimorphic; the males are more brightly-coloured than the females with an elongated second ray in the second dorsal fin and an elongated anal fin. When breeding, the males develop a red nuptial stripe which runs from the snout to the second dorsal fin.[4] The males areterritorial and defend their territories from other males.[3] Over a period of several days, the females lay eggs which stick to aquatic plants by an adhesive thread on the outside of each egg. The larvae hatch after a week to ten days. In the aquarium they reach sexual maturity between 9–12 months old and may have a lifespan of up to 4 years.[4] The spawning season runs from November to January.[7]
The ornate rainbowfish is divided into four genetically distinct populations: the northern mainland population which occurs from Byfield south toTin Can Bay and Fraser Island in Queensland; the Searys Creek population in the area ofRainbow Beach; a population which occurs from theNoosa River in Queensland south toBrunswick River which includes the subpopulations on Moreton, Bribie and Stradbroke Islands; and a fourth in northern New South Wales south of the Brunswick River. These populations are also fragmented within their own geographic areas, and they are threatened by theinvasiveEastern mosquitofishGambusia holbrooki. Other threats include land clearance, habitat degradation[4] and urbanisation.[3] This species is listed as "vulnerable" by theIUCN.[5]
The distribution of the ornate rainbowfish has contracted as a result of urban and rural development, this contraction being exacerbated by the subsequent alterations tohydrology and to the water quality. These factors continue to have negative impacts on populations of this species in a number of localities. Extensive sampling of rivers and streams in mainland south-east Queensland under the auspices ofWildlife Preservation Society of Queensland in the years leading up to 2014 discovered relatively few individual ornate rainbowfish. Due to ecology and geographic distribution of this species, each time a subpopulation is lost it is likely a unique genetic lineage may be being lost too. However, new subpopulations were still being discovered.[8]
The ornate rainbowfish wasdescribed byCharles Tate Regan in 1914 fromtypes collected on Moreton Island.[9] The generic name is acompound noun consisting of theGreek for "slender",rhadinos, and for spine,centron, a reference to the slender and flexible finrays in the dorsal fin. Thespecific nameornatus isLatin and means "decorated".[10]
Rhadinocentrus ornatus is the only species in the genusRhadinocentrus.[11]
The ornate rainbowfish is very closely associated with the warm and peatywallum wetland habitats that its range almost exactly corresponds to that habitat type. Each permanent coastal stream within its range appears to have fish with different colouration or patterning. These subpopulations have evolved in isolation over the last ten millennia as the rising sea levels have cut each population off from those in neighbouring coastal streams.[12]
Rhadinocentrus ornatus is a popularaquarium fish in Australia,[5] having been popular among aquarists who keep the native fish of Australia for many decades,[3] although it appears to be rarely available outside of Australia.[13]
