Cairns Rainbowfish, Cairnsichthys rhombosomoides (Nichols & Raven 1928)

Other Names: Cairns Rainbow Fish, Northern Soft-spined Sunfish, Northern Soft-spined Sun-fish

Cairns Rainbowfish, Cairnsichthys rhombosomoides. Source: Brad Pusey. License: All rights reserved


A small yellowish-brown rainbowfish with with a narrow dark mid-lateral stripe, and a large silvery to yellowish spot on the gill cover. The more brightly coloured males are deeper bodied than females and have elongate dorsal and anal fins with yellowish-orange fin margins, and the caudal fin also has a yellow-orange margin. 

Cite this page as:
Gomon, M.F. & Bray, D.J. 2018, Cairnsichthys rhombosomoides in Fishes of Australia, accessed 24 Aug 2019,

Cairns Rainbowfish, Cairnsichthys rhombosomoides (Nichols & Raven 1928)

More Info


Endemic to the wet tropics in northern Queensland, from the Daintree - Cape Tribulation area, 120 km north of Cairns (16º10´S), to the Innisfail region (17º32´S). 

Founds in the rainforest foothills in small permanent upland streams below 100 m, and small lowland tributaries of larger rivers. 

The Cairns Rainbowfish inhabits shallow swiftly flowing and heavily shaded sandy areas with shelter provided by tree roots, woody debris, leaf litter, undercut banks and aquatic vegetation. 


Meristic features: Dorsal fin V-VII + I, 11-14; Anal fin 1,17-21; Pectoral fin 11-13
Body relatively elongate, laterally compressed; lateral line absent; greatest body depth (adults > 50 mm SL): males 25.7-30.1, females 21.6-28.0; head length 24.6-27.9 in SL; snout length 7.2-8.7 in SL; eye large, diameter 7.3-10.3 in SL; interorbital width 9.9-11.1 in SL; jaws equal; mouth terminal, initially horizontal becoming oblique caudally, large, reaching back to anterior region of eye; outside of mouth with several rows of small conical teeth.
Scales: vertical scale rows 36 to 38; predorsal scales 15 or 16; preopercle-suborbital scales 4 to 8.
Two separate dorsal fins, anal fin long-based; caudal fin emarginate to falcate.


To 8.5 cm SL, commonly to 6 cm. Males larger than females.


Usually yellowish-green with a relatively thin black mid-lateral stripe, pale below. Males more brightly coloured with a yellow margin on the dorsal anal and caudal fins.


Omnivore - feeds on insects and insect larvae, microcrustaceans and algae.


Spawning occurs from April to December with peak spawning from August to October. Females are egg-scatters, depositing their eggs in batches amongst aquatic plants, root-masses and leaf litter. The eggs are small and numerous, and likely to be somewhat adhesive.

The larvae are small at hatching, with little yolk, well-developed eyes, a well-developed feeding apparatus and gut - they commence feeding shortly after hatching.


Rare in aquaria.


IUCN Red List of Threatened Species: Vulnerable.Not listed in Australia.

Populations of Cairns Rainbowfish are highly fragmented and threatened by extended drought and habitat disturbances such as pollution, land clearing and water extraction.


Cairnsichthys is from Cairns, the type locality, and ichthys from the Latin meaning 'fish'. The specific name rhombosomoides is from the Latin rhombosoide, meaning 'shaped like a rhombus'.

Species Citation

Rhadinocentrus rhombosomoides Nichols & Raven, 1928, Am. Mus. Novit. 296: 1. Type locality: Babinda Creek drainage, Queensland.


Gomon, M.F. & Bray, D.J. 2018


Australian Faunal Directory

Cairns Rainbowfish, Cairnsichthys rhombosomoides (Nichols & Raven 1928)


Allen, G. R. 1980. A generic classification of the rainbow-fishes (family Melanotaeniidae). Records of the Western Australian Museum 8: 449-90.

Allen, G.R. & Cross, N.J. (1982). Rainbowfishes of Australia and Papua-New Guinea.  New Jersey : T.F.H. Publications 142 pp.

Allen, G.R. (1989). Freshwater Fishes of Australia.  Neptune, New Jersey : T.F.H. Publications pp. 1–240

Allen, G.R., Midgley, S.H. & Allen, M. (2002). Field guide to the freshwater fishes of Australia.  Perth : Western Australian Museum 394 pp.

Leggett, R. & Merrick, J.R. (1987). Australian Native Fishes for Aquariums.  Artarmon : J.R. Merrick Publications 241 pp.

Kleiberg, T. 1988. The Cairns Rainbowfish Cairnsichthys rhombosomoides (Nichols & Raven). Fishes of Sahul 5(2): 215-216.

Martin, K. C. 2010. Along the Bloomfield Track, North Queensland. In-Stream 19(10):

Martin, K.C. & Barclay, S. 2013. New distribution records for the Cairns Rainbowfish Cairnsichthys rhombosomoides (Melanotaeniidae): implications for conservation of a restricted northern population. aqua, International Journal of Ichthyology 19(3): 155-164.

McGuigan, K., Zhu, D., Allen, G.R. & Moritz, C. (2000). Phylogenetic relationships and historical biogeography of Melanotaeniid fishes in Australia and New Guinea. Australian Journal of Marine and Freshwater Research 51: 713–723.

Merrick, J.R. & Schmida, G.E. (1984). Australian Freshwater Fishes Biology and Management.  Sydney : J.R. Merrick 409 pp. figs 280 col.

Nichols, J.T. & Raven, H.C. (1928). A new melanotaeniin fish from Queensland. Am. Mus. Novit. 296: 1–2 fig. 1

Pusey B., Kennard M. & Arthington A. (2004) Freshwater fishes of north-eastern Australia. CSIRO publishing, Collingwood, Victoria. 684 pp.

Sparks, J.S. & Smith, L.W. (2004). Phylogeny and biogeography of the Malagasy and Australasian rainbowfishes (Teleostei: Melanotaenioidei): Gondwanan vicariance and evolution in freshwater. Molecular Biology and Evolution 33: 719–734.

Thuesen, P.A. 2004. Biological barriers to gene flow and population genetic structure of an endemic rainbow-fish, Cairnsichthys rhombosomoides [Honours Thesis]. Cairns: James Cook University. 89 pp.

Thuesen P.A., B.J. Pusey, D.R. Peck, R. Pearson & B.C. Congdon. (2008) Genetic differentiation over small spatial scales in the absence of physical barriers in an Australian rainforest stream fish. Journal of Fish Biology 72(5): 1174-1187. 

Unmack, P.J., Allen, G.R. & Johnson, G.B. 2013. Phylogeny and biogeography of rainbowfishes (Melanotaeniidae) from Australia and New Guinea. Molecular Phylogenetics and Evolution 67: 15–27.

Quick Facts

CAAB Code:37245002

Conservation:IUCN Vulnerable

Fishing:Aquarium fish

Habitat:Clear freshwater streams

Max Size:8.5 cm SL; 10 cm TL


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