Harlequin Rasbora

Trigonostigma heteromorpha

The harlequin rasbora, Trigonostigma heteromorpha, is a small Southeast Asian schooling fish from slow forest streams, peat swamps, and shaded waters of the Malay Peninsula, Singapore, Sumatra, and nearby regions. Although it is still widely sold under the rasbora name, its current genus reflects a different spawning style from many true Rasbora. The fish is easy to recognize: a warm copper to orange body carries a dark triangular wedge that starts near the middle of the side and broadens toward the tail. Adults stay small, usually around 4 to 5 centimeters, and look best when kept in a group.

In aquariums, harlequin rasboras suit peaceful community tanks with other small, calm fish. A group of at least eight gives them confidence and reduces skittish behavior, while plants, subdued lighting, and open swimming space bring out their color. Captive-bred fish adapt to neutral water, but they still do best in clean, stable conditions and are less comfortable in hard, bright, bare tanks. They eat fine flake, micro pellets, and small frozen or live foods. Breeding is more specialized than many egg scatterers because pairs turn under broad leaves and attach eggs to the underside, often requiring soft, slightly acidic water and a separate spawning setup.