The Australian rainbowfish (Melanotaenia fluviatilis), known less commonly as the Murray River rainbowfish or the crimson-spotted rainbowfish, is a species of freshwater rainbowfish endemic to Australia. They are very colourful, hence their name; males of this species are more colourful than females. Australian rainbowfish are schooling fish and will congregate near logs or riverbanks.
Melanotaenia fluviatilis was originally described by François de Laporte de Castelnau as Aristeus fluviatilis. M. fluviatilis was formerly considered a synonym of M. duboulayi. Authors recognised M. duboulayi and M. fluviatilis either as a single species or separate subspecies, or even as two subspecies of M. splendida. Despite the many similarities between M. duboulayi and M. fluviatilis, they were recognised as separate species in 1986 because of genetic, morphometric, and meristic differences.
Australian rainbowfish reach maximum lengths of 11 cm (4.3 in), but the males are usually no larger than 8.5 cm (3.3 in), while the females usually only grow to 7 cm (2.8 in). The body is elongated, with a small head and large eyes. Australian rainbowfish have two dorsal fins and a pointed anal fin. The caudal (tail) fin is forked shallowly. The fins (excluding the caudal fin) are yellow with dark margins and orange or red markings.
Australian rainbowfish are colourful fish, hence their name. Their sides are silvery-brown, and have a green or silver sheen. A blue stripe extends from the snout to the caudal fin. The other fins are yellow and marked with orange or red. In males, several orange stripes run laterally across the posterior half of the body. Males have red spots on the dorsal, anal and caudal fins, with a blackish margin when breeding.  Females are less intensely coloured, lacking some of the brilliance and red stripes along the caudal peduncle.
Australian rainbowfish are omnivorous. They feed on aquatic and terrestrial invertebrates and some filamentous algae. In captivity, their diet comprises all kinds of live foods, as well as flake food. They may group around logs and grassy riverbanks. They are peaceful in temperament and tend to school. Breeding is described as "easy" in this species.
Distribution and habitat
Australian rainbowfish are freshwater fish native to Australia, occurring in New South Wales and Queensland, especially in the Murray-Darling basin. The Campaspe River and the Goulburn River, VIC, represent the southern distribution limit.
'M. fluviatilis' forms schools in slow-flowing freshwater rivers, wetlands and billabongs. They inhabit rivers, drains, creeks, ponds and reservoirs, and occasionally stagnant water. They inhabit temperature ranges between 22 and 25°C. As their range is the southernmost of all rainbowfishes, Australian rainbowfish are the only species adapted to low winter temperatures of 10 to 15°C.
- Froese, Rainer and Pauly, Daniel, eds. (2010). "Melanotaenia fluviatilis" in FishBase. March 2010 version.
- Froese, Rainer, and Daniel Pauly (eds.). "Common names of Melanotaenia fluviatilis". FishBase.org. Retrieved 23 April 2010.
- Froese, Rainer, and Daniel Pauly (eds.). "Synonyms of Melanotaenia fluviatilis (Castelnau, 1878)". FishBase.org. Retrieved 23 April 2010.
- Pusey, Brad; Mark J. Kennard; Angela H. Arthington (2004). Freshwater fishes of north-eastern Australia. Collingwood: CSIRO Publishing. p. 222. ISBN 0-643-06966-6.
- Butler, Rhett A. "Australian Rainbowfish". Mongabay.com. Retrieved 23 April 2010.
- Gomon, Martin F.; Dianne J. Bray. "Murray River Rainbowfish, Melanotaenia fluviatilis". Fishes of Australia. Retrieved 29 April 2015.
- Baensch, Hans A.; Rudiger Riehl; Hans A. Smith; Eberhard Schulze; Bob Behme (1997). Aquarium Atlas. 1 (6 ed.). Melle: Hans A. Baensch. p. 850. ISBN 3-88244-050-3.
- Fishes of Australia website
- Murray River rainbowfish
- Melanotaenia fluviatilis
- River Murray rainbowfish fact sheet