Harlequin Rasbora
Harlequin Rasbora(Trigonostigma heteromorpha) is one of the most iconic schooling fish in the freshwater hobby — the shimmering copper-orange body offset by a bold, precisely defined black triangular wedge on the rear half of the body is immediately recognizable and has been a staple of the hobby since it was first described by Duncker in 1904. The genus nameTrigonostigma— ‘three-spotted’ — was created in 1999 when this group was separated from the enormous genusRasbora.
Feeding & Care Tip:Sera Vipan Tropical FlakesandHikari Micro Pelletsmake excellent daily staples. Supplement 2–3× per week withHikari Frozen or Freeze-Dried Baby Brine Shrimp,Hikari Frozen or Freeze-Dried Tubifex Worms, orHikari Vibra Bites. Feed small amounts 2–3 times daily.
Native to peat swamp forests and slow-moving blackwater streams across Malaysia, Singapore, southern Thailand, Sumatra, and Borneo. In Singapore, a remnant population survives in Nee Soon Swamp — one of the last remaining pockets of pristine freshwater forest swamp on the island. All five members of the Trigonostigma genus spawn in the same distinctive way: the female inverts to place eggs on the underside of broad-leaved plants, with the male fertilizing immediately below.
Keep in groups of at least 8 — larger groups produce tighter, more synchronized schooling. The copper-orange body and contrasting black triangle are most vivid in soft, slightly acidic water with tannin additions and subdued lighting. One of the finest tetras-and-rasboras for a planted community aquarium — compatible with virtually all peaceful community species.
The spawning behavior of Trigonostigma rasboras is unique and fascinating — the female inverts completely to place eggs on the underside of a broad leaf, then the pair separate and the eggs develop without parental care. Cryptocoryne leaves are the traditional natural spawning site. The Harlequin Rasbora has been a beloved hobby staple for over 120 years — a testament to its combination of striking beauty, peaceful temperament, and adaptability.
Care & Ideal Parameters
| Difficulty | Easy |
| Temperament | Peaceful — active schooling community |
| Typical Adult Size | 2.0 inches (5 cm) |
| Min. Group Size | 8 minimum |
| Ideal Temp | 72–82°F (22–28°C) |
| Ideal pH | 6.0–7.5 |
| Ideal GH | 1–12 dGH |
| Ideal KH | 0–6 dKH |
| Staple Food | Sera Vipan Tropical Flakes; Hikari Micro Pellets |
| Treat / Supplement | Hikari Frozen or Freeze-Dried Baby Brine Shrimp; Hikari Frozen or Freeze-Dried Tubifex Worms; Hikari Vibra Bites |
| Origin | Malay Peninsula, Sumatra, Borneo, southern Thailand, Singapore |
| Notes | Described by Duncker 1904. Trigonostigma genus established 1999 — separated from Rasbora. Female inverts to lay eggs on leaf undersides. Singapore Nee Soon Swamp remnant wild population. In hobby 120+ years. |
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