Rainbowfish

Rainbowfishes (family Melanotaeniidae) are small fishes well suited to aquaria. They are schooling fishes from Australia and New Guinea, related to the silversides (Atherinidae) within which they are sometimes included. Although their ancestors came from the sea, they fill the tetra and minnow niches in the freshwaters of Australia and the neighbouring islands. Many are colourful, and most are quiet and very easily cared for. 

The most commonly seen species belong to the Australian genus Melanotaenia, most of which are 8 to 15 cm (3 to 6 inches) in length when mature. Melanotaenia boesemani, Melanotaenia fluvialitis, and Melanotaenia maccullochi are among the commonest species seen outside of Australia. Adult fish, especially males, are colourful and often develop high backs making the fish look quite impressive. They feed freely on flakes and small pellets, but augmenting the diet with mosquito larvae, small crustaceans, and similar foods on a regular basis will promote good colour. 

Only a little salt is needed for most rainbowfishes. Like kribensis or guppies they are fish of freshwater streams rather than estuaries and aren’t really brackish water fish in the sense of being tolerant of wide changes in salinity. The only species that naturally occurs in brackish water is Melanotaenia nigrans, a species not commonly traded. Most species are never found in brackish waters, so don’t keep these fish in an aquarium with a specific gravity at or above SG 1.005. But they are hardy and tolerant of slightly brackish water, and will do well in a low-salinity aquarium populated with gobies, dwarf cichlids, or livebearers. Rainbowfish are completely inoffensive and mix well with other peaceful fish.