The harlequin rasbora, Trigonostigma heteromorpha
is a small tropical fish in the minnow family Cyprinidae, native to Malaysia, Singapore, Sumatra and southern Thailand. It is a long-time favorite in the aquarium trade. Originally in the genus Rasbora
, in 1999 it was placed as one of four fish with similar body shape and breeding style in a new genus Trigonostigma
(although research is ongoing and Tang et al. suggest synonymizing these genera). Harlequin rasboras grow to a size of about 2 inches long, and eat small zooplankton. They are characterized by the black pigmentation of the back half of their body, which is the shape of a triangle. In the wild they shoal in streams running through peat swamps, which have soft (low mineral containing) water containing high concentrations of tannins and humic acid. Unlike other rasboras, which spawn by scattering their eggs, female fish in genus Trigonostigma
deposit their eggs in small clusters (10-12) on the undersides of leaves, and as she does this the male curls his tail around the females body and fertilizes the eggs. Although adult fish will live happily in aquaria with a neutral or even alkaline pH, breeding requires soft, acidic (pH 6.4) water.
; Tang et al 2010; Wikipedia 2012