Can Harlequin Rasbora live with Molly?
Case-by-case. Watch group sizes, tank size, and feeding zones.
Why Harlequin Rasbora and Molly Don't Make an Easy Pair
They can coexist, but you need to manage the setup carefully. The temperament combination (peaceful+peaceful) can work, but you will need to watch them at feeding time for the first week.
Harlequin Rasbora
Trigonostigma heteromorpha
| Adult Size: | 2.0" |
| Temperament: | peaceful |
| Min Tank: | 10 gal |
| Temperature: | 73-79°F |
| pH Range: | 5.5-7.0 |
Molly
Poecilia sphenops
| Adult Size: | 4.5" |
| Temperament: | peaceful |
| Min Tank: | 20 gal |
| Temperature: | 72-82°F |
| pH Range: | 7.0-8.0 |
Water Parameter Overlap
| Parameter | Harlequin Rasbora | Molly | Overlap |
|---|---|---|---|
| Temperature | 73-79°F | 72-82°F | 6°F ✓ |
| pH | 5.5-7.0 | 7.0-8.0 | No overlap ✗ |
Compatibility Breakdown
Temperament Match: peaceful + peaceful. Both peaceful → minimal conflict.
⚠️ Size Predation Risk: Harlequin Rasbora (2.0") vs Molly (4.5"). A 2.5" gap — the larger fish will view the smaller fish as food.
Score: 60/100 (GOOD ≥80, CAUTION ≥50, RISKY <50).
🔧 Tank Setup Requirements (for Both)
- Minimum tank: 20 gallons — sized for the larger fish in the pair.
- Temperature: keep it between 73°F and 79°F.
- pH: no shared range. One species will be outside its tolerance regardless of what you set.
- Hiding spots: essential for Harlequin Rasbora — caves, plants, or driftwood to retreat when feeling stressed.
- Water changes: 25% weekly minimum. Two species mean double the bioload.
🔧 Tank Stocking Calculator
Enter tank size to calculate safe stocking levels:
Recommended Equipment
Based on tank size 20+ gallons:
Quiet internal filter for 20-gallon tanks
Explore Related Checks
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Accuracy note: This tool uses expert rules + FishBase.org data. Individual fish behavior varies — a peaceful individual Harlequin Rasbora may act differently from its species average. Always observe, quarantine new arrivals for 2-4 weeks, and avoid overcrowding. If a pairing says CAUTION, start with a smaller group and a lid.