Rhadinocentrus ornatus

Rhadinocentrus ornatus [Carland Creek, Qld] - photo© Neil Armstrong

Regan, 1914
Ornate Rainbowfish

Description
Rhadinocentrus ornatus was described by Regan in 1914 and is the only species currently recognised within its genus. They have been a popular aquarium fish with Australian native fish enthusiasts for many decades. Their popularity in the international hobby has been particularly low. I believe that this is mainly due to lack of availability more so than any other factor. It has only been in the last decade that they have taken the attention of the international aquarium hobby.

Distribution & Habitat
Rhadinocentrus ornatus is a sub-tropical species and were first collected from Moreton Island, a sand dune island off the south Queensland coast in Moreton Bay. The type description of Rhadinocentrus ornatus was from a few specimens collected "from a pond on Moreton Island by the signal station operator at Cowan Cowan". A 1924 survey of the island, noted that Rhadinocentrus ornatus were found in swamps and unnamed streams south of the lighthouse.

The first report of Rhadinocentrus ornatus being found on the mainland was in an Aquarium & Terrarium Society of Queensland excursion report in 1927. They were found in an outer southside suburb of Brisbane. Later that same year they were reportedly found in the Pimpama and Broadwater areas in what is now know as the 'Gold Coast' in southern Queensland. They were commonly known as the 'Moreton Island Sunfish' and were very popular with early native fish enthusiasts.

Rhadinocentrus ornatus [Seary's Creek, Qld] - photo© Günther Schmida

Today we know that they have patchy distribution through coastal drainages of Queensland and New South Wales. It has a distribution that includes Fraser, Moreton and Stradbroke Islands, a group of islands off the southern Queensland coast, and patchy distribution along the narrow coastal plains of eastern Australia. Its range is nearly continuous amongst the unconnected coastal river basins from the Nambucca River catchment in the south to Fraser Island in the north. In the Fraser Island - Tin Can Bay area, there is a break in the distribution of over 350 km to a disjunct northern population in the Byfield area (Water Park Creek) near Yeppoon.

Rhadinocentrus ornatus congregate in small schools and occupy small, slowly moving creeks, quiet backwaters of coastal streams and marshy swamps around melaleuca forest, usually over a sandy substrate, where water temperatures range from 20-28°C. However, they are known to survive water temperatures as low as 8°C. They are often abundant in slow and unpolluted, tannin-stained, acidic (pH 4.4-6.8) creeks and lakes. They may be found on their own or with other small-bodied native fishes. Many habitats occupied by Rhadinocentrus ornatus also contained individuals of Nannoperca oxleyana, a species listed as endangered. They are usually found around marginal vegetation, submerged logs, or branches. Although also found in rainforest streams, it is mostly a denizen of the 'wallum', which is low, sandy, coastal heathland of south-east Queensland and northern New South Wales.

Rhadinocentrus ornatus can still be found in reasonably large numbers throughout their range. However, habitat alteration and urban development have and are still having negative impacts in several areas. The introduced Mosquitofish (Gambusia holbrooki), which are tolerant of a wide range of environmental conditions and breeds rapidly, may displace native species such as Rhadinocentrus ornatus, because both species feed substantially on terrestrial insects at the waters surface.

Rhadinocentrus ornatus [Evans River Catchment, NSW] - photo© Günther Schmida

Biology
Rhadinocentrus ornatus is a small, slender, and laterally compressed fish, with two dorsal fins that are very close together; the first much smaller than the second. They exhibit considerable colour variations over their geographical range. Generally the body is semi-transparent with two rows of black scales in the mid-lateral region. The iridescent scales immediately below the dorsal fin and above the lateral line can be either red or metallic pale blue. The dorsal, anal, caudal, and pelvic fins are generally red with black edges. Some morphs have blue fins and a yellow coloured form has been reported from Stradbroke Island. The Stradbroke Island form showed a distinctive black striped pattern on the sides of the body giving the fish an overall dark colouration of the body. Females are not quite so highly coloured. They may reach a maximum size of 7 cm SL, but usually they are less than 5 cm.

Rhadinocentrus ornatus generally spawn between October and December, with females producing between 10-20 eggs each day for several days. Eggs adhere to fine-leaved plants or among the roots of floating vegetation. They are essentially a carnivore, feeding on a variety of terrestrial and aquatic insects, insect larvae, and small aquatic crustaceans. The dorsally projected jaws are well adapted for surface feeding. This is reflected in their natural diet, which consists largely of terrestrial insects. Algae and pollen (mostly pollen) also appear to be a major alternative food.

Rhadinocentrus ornatus [Ballina Region, NSW] - photo© Günther Schmida

Keeping & Caring
In captivity, Rhadinocentrus ornatus is a fish that requires a little more attention than most other Rainbowfishes. They can be maintained and bred in water conditions that are suitable for most aquarium species. However, it is better if they are maintained at a temperature range of 20-28°C; pH 6.0-7.0; and hardness from 5-100 ppm. They will display their best colouration if maintained in a well-planted aquarium with water that has been stained dark, either by using aquarium peat in the filter or one of the commercial products available for this purpose.

Breeding Rhadinocentrus is similar to most Rainbowfishes in captivity. Eggs will hatch in 6 to 10 days at a temperature of 23-28°C. They have a very special beauty and will make an impressive display when maintained in an aquarium of their own, and in a group of around 10 to 20 individuals, particularly if maintained under aquarium conditions that will show their iridescent reflective colouration.

Contents

Rainbowfishes

Introduction

Scientific Names

Rainbowfish Species