The harlequin rasbora a small fish belonging to the family Cyprinidae, subfamily Rasborinae, which was originally given the scientific name of Rasbora heteromorpha. The specific name heteromorpha, translating from the Greek as "differently shaped", alludes to the fact that the body shape of this species differs from that of other members of the genus Rasbora, and as a consequence of this and assorted other factors (including the difference in breeding technique), the fish was assigned to a new genus, Trigonostigma, and is thus now known to science as Trigonostigma heteromorpha. The common name for this fish, harlequin rasbora or harlequin fish, alludes to the black triangular patch upon the body, which is reminiscent of the patterns found on the costume of a harlequin.
The species is a popular aquarium fish, and is perhaps the best known of all the rasboras. The species has been in circulation among aquarists since 1934.