Compatibility Overview
Harlequin Rasbora and Oscar can potentially coexist, but the combination requires careful attention. Some combination of water parameter differences, size mismatch, or temperament issues make this pair challenging. A larger tank (minimum 100 gallons), dense planting, and close monitoring are essential.
| Factor | Harlequin Rasbora | Oscar | Verdict |
|---|---|---|---|
| Temperature | 72–81°F | 74–81°F | ✅ 74–81°F |
| pH Range | 5.5–7.5 | 6.0–8.0 | ✅ 6.0–7.5 |
| Temperament | peaceful | aggressive | ❌ Risk |
| Adult Size | 1.75 in | 14 in | ❌ 8× difference |
| Min. Group | 8+ | 1+ | See below |
| Min. Tank Size | 100 gallons (for both species) | — | |
✅ Compatibility Positives
⚠️ Caution Points
Species Profiles
Harlequin Rasbora — Trigonostigma heteromorpha
Active mid-level schooling fish with a distinctive black triangular patch. One of the best all-around community tank fish.
→ Full Harlequin Rasbora care guide
Oscar — Astronotus ocellatus
Intelligent but aggressive cichlids that will eat any fish small enough to fit in their mouth. Require large tanks (75+ gallons) and robust tank mates.
Frequently Asked Questions
Can Harlequin Rasbora live with Oscar?
With significant caution and a larger tank. Harlequin Rasbora and Oscar can potentially coexist, but the combination requires careful attention. Some combination of water parameter differences, size mismatch, or temperament issues make this pair challenging. A larger tank (minimum 100 gallons), dense planting, and close monitoring are essential.
What tank size do I need for Harlequin Rasbora and Oscar together?
A minimum of 100 gallons is recommended for keeping Harlequin Rasbora and Oscar together. A larger tank improves water stability and reduces territorial conflict.
What temperature suits both Harlequin Rasbora and Oscar?
74–81°F
Is a Harlequin Rasbora aggressive toward a Oscar?
Harlequin Rasbora is peaceful and Oscar is aggressive. Large size difference: Oscar (14 in) may predate on Harlequin Rasbora (1.75 in).