Can Jack Dempsey live with Lyretail Killifish?
High risk due to water mismatch, aggression, or predation.
Why Jack Dempsey and Lyretail Killifish Don't Make an Easy Pair
The size gap is 7.5" — Jack Dempsey (10.0") and Lyretail Killifish (2.5"). A fish that fits in another fish's mouth will eventually end up there.
Jack Dempsey
Rocio octofasciata
| Adult Size: | 10.0" |
| Temperament: | aggressive |
| Min Tank: | 55 gal |
| Temperature: | 72-82°F |
| pH Range: | 6.5-8.0 |
Lyretail Killifish
Aphyosemion australe
| Adult Size: | 2.5" |
| Temperament: | peaceful |
| Min Tank: | 10 gal |
| Temperature: | 72-77°F |
| pH Range: | 6.0-7.0 |
Water Parameter Overlap
| Parameter | Jack Dempsey | Lyretail Killifish | Overlap |
|---|---|---|---|
| Temperature | 72-82°F | 72-77°F | 5°F ✓ |
| pH | 6.5-8.0 | 6.0-7.0 | 0.5 ✓ |
Compatibility Breakdown
Temperament Match: aggressive + peaceful. One aggressive → predation/nipping risk.
⚠️ Size Predation Risk: Jack Dempsey (10.0") vs Lyretail Killifish (2.5"). A 7.5" 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: 45.0/100 (GOOD ≥80, CAUTION ≥50, RISKY <50).
🔧 Tank Setup Requirements (for Both)
- Minimum tank: 55 gallons — sized for the larger fish in the pair.
- Temperature: keep it between 72°F and 77°F.
- pH: maintain 6.5 – 7.0.
- 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 55+ gallons:
Floating pellet for medium to large cichlids
Explore Related Checks
See what else works with these fish:
⚠️ Common Reasons This Pairing Fails in Practice
- Size-based predation: The 7.5" 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.
- Aggression risk: An aggressive species will dominate feeding zones and chase the other fish into hiding. Chronic stress weakens the immune system and shortens lifespan.
- 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.
Tools & Resources
Accuracy note: This tool uses expert rules + FishBase.org data. Individual fish behavior varies — a aggressive individual Jack Dempsey 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.