Cardinal Rasbora
Cardinal Rasbora
Cardinal Rasbora (Sundadanio rubescens) is a tiny and vividly colored nano fish from the blackwater peat swamps of Borneo — the vivid red body with iridescent blue-green lateral stripe and red fins in males creates a fish that punches well above its size in visual impact. The 'Cardinal' name references the resemblance to the Cardinal Tetra's red-and-blue color scheme in miniature. Formerly classified as Microrasbora rubescens, this species was moved to the genus Sundadanio following taxonomic revision.
Feeding & Care Tip: Hikari Micro Pellets (crushed or soaked briefly) and Sera Vipan Baby make excellent daily staples. Supplement 2–3× per week with Hikari Frozen or Freeze-Dried Baby Brine Shrimp and Hikari Frozen Daphnia. Feed small amounts 2–3 times daily.
Native to the blackwater peat swamp forests of Borneo — the same type of habitat as the Chili Rasbora and Phoenix Rasbora, with extremely soft, acidic, tannin-stained water. A mature blackwater setup with Indian almond leaves, dark substrate, and very soft acidic water is essential for the best coloration.
Keep in groups of at least 10 in a nano blackwater setup. Compatible with other nano species and dwarf shrimp. Any larger or more active fish will stress these tiny fish. Males display their most vivid red-and-blue coloration in competition — a large group in a dark-substrate planted aquarium is stunning.
A close relative of the Neon Blue and Neon Red Rasboras in the Sundadanio genus — all three are excellent nano blackwater rasboras with distinct coloration and the same essential care requirements.
Care & Ideal Parameters
| Difficulty | Easy — Moderate |
| Temperament | Peaceful — nano blackwater community |
| Typical Adult Size | 1.0 inch (2.5 cm) |
| Min. Group Size | 10 minimum |
| Ideal Temp | 73–82°F (23–28°C) |
| Ideal pH | 4.0–7.0 |
| Ideal GH | 0–10 dGH |
| Ideal KH | 0–5 dKH |
| Staple Food | Hikari Micro Pellets (crushed/soaked); Sera Vipan Baby |
| Treat / Supplement | Hikari Frozen or Freeze-Dried Baby Brine Shrimp; Hikari Frozen Daphnia |
| Origin | Blackwater peat swamp forests of Borneo |
| Notes | Formerly Microrasbora rubescens — moved to genus Sundadanio. Red body + blue-green lateral stripe. 'Cardinal' name = resemblance to Cardinal Tetra. Close relative of Neon Blue and Neon Red Rasboras. |
