The harlequin rasbora (Trigonostigma heteromorpha) is a small fish in the family Cyprinidae The species became an instant favorite among aquarists after its introduction in the early 1900s and is the best known and most widely kept species among the rasboras. In 1935, an image of a trio of harlequin rasboras, stamped in 14k gold, would grace the cover of the first edition of William T. Innes's classic Exotic Aquarium Fishes and would remain so through all 19 editions.
hese fish prefer softer, acidic waters and although they can cope in a neutral or slightly alkaline community tank, it’s worth remembering that some pathogens fare better in alkaline waters. Aim for a pH of between 5.0 and 7.0, with a hardness of below 12°DH.
Set the temperature somewhere between 22-25°C/72-77°F to recreate wild conditions and keep water flow light. Harlequins do not thrive in high, rushing water flows and may actively avoid areas in the tank where they get buffeted.