From Microcosm Aquarium Explorer
One of the classic aquarium fishes, the Harlequin Rasbora is considered by many to be the Rasbora and an ideal choice for the peaceful community. The distinctive black “triangle on its side” is a hallmark of the species, but a second species, T. espei, has similar markings and is often sold as the Harlequin, although it is much slimmer.
Other common name(s):
Habitat: The Harlequin Rasbora prefers an environment with areas of dense vegetation and driftwood, lots of open space for swimming, a dark substrate, and a cover of floating plants to produce subdued lighting.
Maximum length: 5 cm (2 in)
Minimum aquarium size: 76 L (20 gal)
Water: Freshwater 22 °C (72 °F) - 26 °C (79 °F)
General swimming level: Midwater to top.
Carnivore. The Harlequin Rasbora will enthusiastically accept most prepared foods, including good-quality flakes and pellets, but will need occasional feedings of frozen and live foods, such as Daphnia and brine shrimp, to do well in the aquarium.
The Harlequin Rasbora is an active, schooling species that should be kept in groups of at least four (even more will make them feel more comfortable and provide a stunning display), with other similar-size peaceful tankmates, including many of the smaller barbs, danios or other rasboras.
Harlequin Rasboras are egglayers that deposit their adhesive spawns on the undersides of leaves.