Harlequin Rasbora

Looks how to spot one

Small scaled cyprinid with a deep, diamond-shaped body

A compact, lozenge-shaped fish with a warm copper to pinkish-orange body. Its signature mark is a bold black triangle on the rear half of the body that narrows towards the tail. The fins carry a reddish tint, and the forked tail has red outer edges with clear centres. Males tend to show richer colour and a sharper, slightly larger black patch, while females are rounder.321

Personality what they are like

An exceptionally gentle and sociable fish that rarely bothers anything else in the tank. It is at its most confident and colourful when it can swim with a decent-sized group of its own kind.23

Daily activity how busy a day looks

An active swimmer that spends its time in the open middle area of the tank. It enjoys calm to gently moving water with plenty of plants around the edges and free space to shoal.21

Grooming and care the hands-on bits

Keep the water soft, warm and slightly acidic to neutral, with regular partial water changes. Leaf litter, driftwood and subdued lighting mimic its peat-swamp home and bring out its colour.23

Home where they are happiest

Aquarium with a footprint of at least 60 x 30 cm (about 54 litres). Temperature around 21-28 C (FishBase gives 22-25 C), pH about 5.0-7.5 (FishBase 5.0-7.0), hardness roughly 1-12 dGH. A well-planted tank with some broad-leaved plants and open swimming water suits it best.21

Food basics what goes in the bowl

In nature it hunts small insects, worms, crustaceans and other tiny animals. In the aquarium it readily takes quality flake and small granules, and benefits from regular live or frozen treats such as daphnia, bloodworm, brine shrimp and mosquito larvae.213

Company who they like around

A schooling species that should live in a group; Seriously Fish suggests at least 8-10, Wikipedia at least 6 and FishBase 5 or more. Good tankmates are other small, peaceful fish of similar size.231

The story where it all began

The harlequin rasbora comes from slow forest streams and peat swamps of the Malay Peninsula and nearby islands, where the water is stained brown by humic acids and very low in minerals, much like South American blackwater. It was described by the German zoologist Georg Duncker in 1904 as Rasbora heteromorpha; in 1999 Kottelat and Witte moved it into the genus Trigonostigma, whose name points to its triangular marking. The fish reached European aquarists in the early 1900s and became a favourite almost at once. Its standing in the hobby was cemented when its image, stamped in gold, appeared on the cover of William T. Innes's classic book Exotic Aquarium Fishes in 1935, staying there through all 19 editions. It remains one of the most familiar and long-lasting species in fishkeeping.23

Recognised by the official bits

IUCN Red List

Assessed as Least Concern (January 2019)1

FishBase

Listed as highly commercial in both fisheries and the aquarium trade1