Can Emperor Tetra live with Swordtail?
High risk due to water mismatch, aggression, or predation.
Why Emperor Tetra and Swordtail Don't Make an Easy Pair
The size gap is 3.0" — Emperor Tetra (2.0") and Swordtail (5.0"). A fish that fits in another fish's mouth will eventually end up there.
Emperor Tetra
Nematobrycon palmeri
| Adult Size: | 2.0" |
| Temperament: | peaceful |
| Min Tank: | 20 gal |
| Temperature: | 73-82°F |
| pH Range: | 5.5-7.0 |
Swordtail
Xiphophorus helleri
| Adult Size: | 5.0" |
| Temperament: | semi-aggressive |
| Min Tank: | 20 gal |
| Temperature: | 72-78°F |
| pH Range: | 7.0-8.0 |
Water Parameter Overlap
| Parameter | Emperor Tetra | Swordtail | Overlap |
|---|---|---|---|
| Temperature | 73-82°F | 72-78°F | 5°F ✓ |
| pH | 5.5-7.0 | 7.0-8.0 | No overlap ✗ |
Compatibility Breakdown
Temperament Match: peaceful + semi-aggressive. Semi-aggressive → watch territory and feeding.
⚠️ Size Predation Risk: Emperor Tetra (2.0") vs Swordtail (5.0"). A 3.0" gap — the larger fish will view the smaller fish as food.
Score: 40/100 (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 78°F.
- pH: no shared range. One species will be outside its tolerance regardless of what you set.
- Hiding spots: essential for Emperor Tetra — 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:
Micro pellet food for small tetras
Explore Related Checks
See what else works with these fish:
⚠️ Common Reasons This Pairing Fails in Practice
- Size-based predation: The 3.0" 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.
- 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 peaceful individual Emperor Tetra 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.