The rainbowfish are a family (Melanotaeniidae) of small, colourful, freshwater fish found in northern and eastern Australia, New Guinea, islands in Cenderawasih Bay, and the Raja Ampat Islands.
The largest rainbowfish genus, Melanotaenia, derives from the ancient Greek melano (black) and taenia (banded). Translated, it means “black-banded”, and is a reference to the often striking lateral black bands that run along the bodies of those in the Melanotaenia genus.
Rainbowfish are usually less than 12 cm (4.7 in) in length, with some species measuring less than 6 cm (2.4 in), while one species, Melanotaenia vanheurni, reaches lengths of up to 20 cm (7.9 in). They live in a wide range of freshwater habitats, including rivers, lakes, and swamps. Although they spawn all year round, they lay a particularly large number of eggs at the start of the local rainy season. The eggs are attached to aquatic vegetation, and hatch seven to 18 days later. Rainbowfish are omnivorous, feeding on small crustaceans, insect larvae, and algae.
Rainbowfish are popular aquarium fish along with Pseudomugil blue-eyes, which are another small, colourful fish found in a similar range and habitats. In the wild, some rainbowfish populations have been severely affected by the aggressive introduced eastern mosquitofish (Gambusia holbrooki), tilapia cichlids, and pollution.
Rainbowfish usually do best with tropical community fish, such as tetras, guppies, and other rainbowfish. However, two males may battle at breeding season. Only one male should therefore be kept per tank. Rainbowfish usually eat floating flakes in captivity, because in the wild they will often eat insects floating on the surface.