Ornate rainbowfish

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Ornate rainbowfish
Rhadinocentrus ornatus Searys Ck male.JPG
male from Searys Creek, southeast Queensland, Australia
Rhadinocentrus ornatus Searys Ck female.JPG
female from Searys Creek, southeast Queensland, Australia
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Atheriniformes
Family: Melanotaeniidae
Subfamily: Melanotaeniinae
Genus: Rhadinocentrus
Regan, 1914 [1]
R. ornatus
Binomial name
Rhadinocentrus ornatus
Regan, 1914

The ornate rainbowfish (Rhadinocentrus ornatus) is a species of rainbowfish endemic to an area in eastern Australia, where it is native to coastal regions and sandy offshore islands in southern Queensland and northern New South Wales. It is the only known member of its genus. It is a popular aquarium fish.

Rainbowfish family of fish (Melanotaeniidae)

The rainbowfish are a family, Melanotaeniidae, of small, colourful, freshwater fish found in northern and eastern Australia, New Guinea, islands in Cenderawasih Bay the Raja Ampat Islands in Indonesia and in Madagascar.

Endemism Ecological state of being unique to a defined geographic location or habitat

Endemism is the ecological state of a species being unique to a defined geographic location, such as an island, nation, country or other defined zone, or habitat type; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere. The extreme opposite of endemism is cosmopolitan distribution. An alternative term for a species that is endemic is precinctive, which applies to species that are restricted to a defined geographical area.

Australia Country in Oceania

Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. It is the largest country in Oceania and the world's sixth-largest country by total area. The neighbouring countries are Papua New Guinea, Indonesia, and East Timor to the north; the Solomon Islands and Vanuatu to the north-east; and New Zealand to the south-east. The population of 26 million is highly urbanised and heavily concentrated on the eastern seaboard. Australia's capital is Canberra, and its largest city is Sydney. The country's other major metropolitan areas are Melbourne, Brisbane, Perth, and Adelaide.



The ornate rainbowfish is a small, slender and rather elongated species of rainbowfish. It has two dorsal fins that are only narrowly separated, and the first dorsal fin is considerably smaller than the second. [2] There are 3 to 5 thin, soft spines in the first dorsal fin while the second dorsal fin has 11–15 segmented rays. [3] 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 have iridescent scales above the lateral line and just below the dorsal fin, and these can be either red or a metallic light blue. The dorsal, anal and caudal fins are normally blue, although are sometimes red, and have black edges. [2] 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 on Stradbroke Island, [3] while another population on that island had distinctive black stripes on the flanks which created an overall dark colouration. [2] 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). [4]

Dorsal fin The fin on the dorsal of fish and cetaceans

A dorsal fin is a fin located on the back of most marine and freshwater vertebrates such as fishes, cetaceans, and the (extinct) ichthyosaur. Most species have only one dorsal fin, but some have two or three.

Iridescence property in which fine colors, changeable with the angle of view or angle of illumination, are produced on a surface by the interference of light that is reflected from both the front and back of a thin film

Iridescence is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfly wings and seashells, as well as certain minerals. It is often created by structural coloration.

Lateral line

The lateral line, also called lateral line system (LLS) or lateral line organ (LLO), is a system of sense organs found in aquatic vertebrates, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelial cells, known as hair cells, which respond to displacement caused by motion and transduce these signals into electrical impulses via excitatory synapses. Lateral lines serve an important role in schooling behavior, predation, and orientation. Fish can use their lateral line system to follow the vortices produced by fleeing prey. Lateral lines are usually visible as faint lines of pores running lengthwise down each side, from the vicinity of the gill covers to the base of the tail. In some species, the receptive organs of the lateral line have been modified to function as electroreceptors, which are organs used to detect electrical impulses, and as such, these systems remain closely linked. Most amphibian larvae and some fully aquatic adult amphibians possess mechanosensitive systems comparable to the lateral line.


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 the Great Dividing Range from near Maryborough to Coffs Harbour. The species distribution extends to sandy islands of southern Queensland including Bribie, Fraser, Moreton and North Stradbroke Islands. [2] [3] On the mainland its distribution is continuous in the southern part of its range but there is a disjunct population in the Byfield area which is separated from the southern population by 350 kilometres (220 mi). [2]

Great Dividing Range mountain range in the Australian states of Queensland, New South Wales and Victoria

The Great Dividing Range, or the Eastern Highlands, is Australia's most substantial mountain range and the fifth longest land-based range in the world. It stretches more than 3,500 kilometres (2,175 mi) from Dauan Island off the northeastern tip of Queensland, running the entire length of the eastern coastline through New South Wales, then into Victoria and turning west, before finally fading into the central plain at the Grampians in western Victoria. The width of the range varies from about 160 km (100 mi) to over 300 km (190 mi). The Greater Blue Mountains Area, Gondwana Rainforests, and Wet Tropics of Queensland World Heritage Areas are located in the range.

Maryborough, Queensland City in Queensland, Australia

Maryborough is a city and a suburb in the Fraser Coast Region, Queensland, Australia. It is located on the Mary River in Queensland, Australia, approximately 255 kilometres (160 mi) north of the state capital, Brisbane. The city is served by the Bruce Highway. It is closely tied to its neighbour city Hervey Bay which is approximately 30 kilometres (20 mi) northeast. Together they form part of the area known as the Fraser Coast. As of June 2015 Maryborough had an estimated urban population of 27,846. The city was the location for the 2013 Australian Scout Jamboree.

Coffs Harbour City in New South Wales, Australia

Coffs Harbour is a city on the Mid North Coast of New South Wales, Australia, 540 km (340 mi) north of Sydney, and 390 km (240 mi) south of Brisbane. It is one of the largest urban centres on the North Coast, with an estimated population of 71,822 in 2018.

Habitat and biology

Ornate rainbowfish inhabit freshwater creeks, streams, ponds and dune lakes in the coastal dune habitat locally known as wallum. Their typical habitat is sandy coastal areas where they are found in sluggish, acid waters stained with tannins from vegetation falling into the water where there is woody debris in the water, grassy banks, and thick submerged and emergent vegetation. [3] In these habitats the ornate rainbowfish prefers to be in cover among submerged woody debris, in grassy banks and reeds; and within waterlily roots. [4] It has also been recorded in clear streams with a slow current and little or no vegetation in gallery forests. [3] This species can tolerate very soft waters and is known to live in water as acidic as orange juice. [5]


Wallum, or wallum country, is an Australian ecosystem of coastal south-east Queensland, extending into north-eastern New South Wales. It is characterised by flora-rich shrubland and heathland on deep, nutrient-poor, acidic, sandy soils, and regular wildfire. Seasonal changes in the water table due to rainfall may create swamps. The name is derived from the Kabi word for the wallum banksia.

<i>Nymphoides</i> genus of plants

Nymphoides, or floatingheart, is a genus of aquatic flowering plants in the family Menyanthaceae. The genus name refers to their resemblance to the water lily Nymphaea. Nymphoides are aquatic plants with submerged roots and floating leaves that hold the small flowers above the water surface. Flowers are sympetalous, most often divided into five lobes (petals). The petals are either yellow or white, and may be adorned with lateral wings or covered in small hairs. The inflorescence consists of either an umbellate cluster of flowers or a lax raceme, with internodes occurring between generally paired flowers.

Gallery forest Type of riparian forest in dry regions

Gallery forests are forests that form as corridors along rivers or wetlands and project into landscapes that are otherwise only sparsely treed such as savannas, grasslands, or deserts.

This species congregates in small schools, especially where the habitat is clear, slow, shady streams over sands. These may be mixed schools with Nannoperca oxleyana and Pseudomugil mellis . [2] This omnivorous species feeds mainly from the surface, and its diet consists of crustaceans, aquatic and terrestrial insects, pollen, algae and organic detritus. [3] It is sexually 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. [3] The males are territorial and defend their territories from other males. [2] 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. [3] The spawning season runs from November to January. [6]

Nannoperca oxleyana, commonly known as the Oxleyan pygmy perch, is a species of temperate perch endemic to Australia. It occurs in the coastal drainages of eastern Australia, being found in dune lakes, ponds, creeks, and swamps with plentiful vegetation to provide shelter. The waters in which it lives are often dark and acidic. It preys upon aquatic insects and their larvae, as well as planktonic crustaceans and even algae. This species can reach 7.5 cm (3.0 in) SL, though most do not exceed 4 cm (1.6 in). It can also be found in the aquarium trade.

Sexual dimorphism condition where the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs

Sexual dimorphism is the condition where the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs. The condition occurs in many animals and some plants. Differences may include secondary sex characteristics, size, weight, color, markings, and may also include behavioral and cognitive differences. These differences may be subtle or exaggerated, and may be subjected to sexual selection. The opposite of dimorphism is monomorphism.


The ornate rainbowfish is divided into four genetically distinct populations: the northern mainland population which occurs from Byfield south to Tin Can Bay and Fraser Island in Queensland; the Searys Creek population in the area of Rainbow Beach; a population which occurs from the Noosa River in Queensland south to Brunswick 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 the invasive Eastern mosquitofish Gambusia holbrooki. Other threats include land clearance, habitat degradation [3] and urbanisation. [2] This species conservation status has not been evaluated by the IUCN. [4]

Rainbow Beach, Queensland Town in Queensland, Australia

Rainbow Beach is a coastal town in the Wide Bay–Burnett region of Queensland, Australia, east of Gympie. At the 2011 census, Rainbow Beach had a population of 1,103. It is a popular tourist destination, both in its own right and as a gateway to Fraser Island.

Noosa River river in South East Queensland, Australia

The Noosa River is a river situated in South East Queensland. The catchment starts in Wahpoonga Range near Mount Elliot in the coastal Great Sandy National Park and meanders south through a lakes district around Tewantin.

Brunswick River (New South Wales) barrier estuary in New South Wales, Australia

Brunswick River is an open mature wave dominated barrier estuary, located in the Northern Rivers region of New South Wales, Australia.

The distribution of the ornate rainbowfish has contracted as a result of urban and rural development, this contraction being exacerbated by the subsequent alterations to hydrology 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 of Wildlife 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. [7]

Taxonomy and etymology

The ornate rainbowfish was described by Charles Tate Regan in 1914 from types collected on Moreton Island. [8] The generic name is a compound noun consisting of the Greek for "slender", rhadinos, and for spine, centron, a reference to the slender and flexible finrays in the dorsal fin. The specific name ornatus is Latin and means "decorated". [9]

Rhadinocentrus ornatus is the only species in the genus Rhadinocentrus. [10]

The ornate rainbowfish is very closely associated with the warm and peaty wallum 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. [11]

As an aquarium fish

Rhadinocentrus ornatus is a popular aquarium fish in Australia, [4] having been popular among aquarists who keep the native fish of Australia for many decades, [2] although it appears to be rarely available outside of Australia. [12]

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Moreton Bay bay in Queensland, Australia

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Speartooth shark species of fish

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Ornate wobbegong species of shark (Orectolobus ornatus)

The ornate wobbegong is a species of carpet shark that lives in Australia and possibly other countries in the Western Pacific Ocean. It is coloured golden brown, yellow-green and blueish-grey, and it grows to about 2.0–2.5 metres (6.6–8.2 ft). Described by Charles Walter De Vis in 1883, it is similar in appearance to other Australian wobbegongs and has previously been classified as the same species as the Gulf wobbegong. It is a nocturnal species, hunting at night, and it can bite humans when disturbed. The International Union for Conservation of Nature has listed it as a least-concern species.

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<i>Melanotaenia duboulayi</i> species of fish

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