Can Lyretail Killifish live with Molly?
Case-by-case. Watch group sizes, tank size, and feeding zones.
Why Lyretail Killifish 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.
Lyretail Killifish
Aphyosemion australe
| Adult Size: | 2.5" |
| Temperament: | peaceful |
| Min Tank: | 10 gal |
| Temperature: | 72-77°F |
| pH Range: | 6.0-7.0 |
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 | Lyretail Killifish | Molly | Overlap |
|---|---|---|---|
| Temperature | 72-77°F | 72-82°F | 5°F ✓ |
| pH | 6.0-7.0 | 7.0-8.0 | No overlap ✗ |
Compatibility Breakdown
Temperament Match: peaceful + peaceful. Both peaceful → minimal conflict.
⚠️ Size Predation Risk: Lyretail Killifish (2.5") vs Molly (4.5"). A 2.0" gap — the larger fish will view the smaller fish as food.
⚠️ Diet Conflict: A carnivore sharing water with a fish small enough to fit in its mouth is a waiting game. Feed generously, but the risk is structural — not something you can manage meal by meal.
Score: 50/100 (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 72°F and 77°F.
- pH: no shared range. One species will be outside its tolerance regardless of what you set.
- Hiding spots: essential for Lyretail Killifish — 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
See what else works with these fish:
⚠️ Common Reasons This Pairing Fails in Practice
- Size-based predation: The 2.0" size gap means the larger fish may eat the smaller one once it grows to full size. This is not fixable with more hiding spots.
- Diet-driven aggression: A carnivore sharing a tank with bite-sized tank mates creates structural risk — no amount of generous feeding eliminates the instinct to hunt.
- Overcrowding: Even compatible species fail in tanks that are too small. Double the species means double the bioload — 25% weekly water changes are the minimum.
- Inadequate acclimation: Adding both species on the same day without quarantine is a common mistake. Always drip-acclimate new arrivals and quarantine for 2–4 weeks.
- Mismatched feeding: Lyretail Killifish is a carnivore while Molly is a omnivore. Use targeted feeding zones and sinking vs. floating food to ensure both get proper nutrition.
Tools & Resources
Accuracy note: This tool uses expert rules + FishBase.org data. Individual fish behavior varies — a peaceful individual Lyretail Killifish 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.