Can Swordtail live with Threadfin Butterflyfish?
High risk due to water mismatch, aggression, or predation.
Why Swordtail and Threadfin Butterflyfish Don't Make an Easy Pair
The size gap is 3.0" — Swordtail (5.0") and Threadfin Butterflyfish (8.0"). A fish that fits in another fish's mouth will eventually end up there.
Swordtail
Xiphophorus helleri
| Adult Size: | 5.0" |
| Temperament: | semi-aggressive |
| Min Tank: | 20 gal |
| Temperature: | 72-78°F |
| pH Range: | 7.0-8.0 |
Threadfin Butterflyfish
Chaetodon auriga
| Adult Size: | 8.0" |
| Temperament: | peaceful |
| Min Tank: | 75 gal |
| Temperature: | 74-82°F |
| pH Range: | 8.1-8.4 |
Water Parameter Overlap
| Parameter | Swordtail | Threadfin Butterflyfish | Overlap |
|---|---|---|---|
| Temperature | 72-78°F | 74-82°F | 4°F ✓ |
| pH | 7.0-8.0 | 8.1-8.4 | No overlap ✗ |
Compatibility Breakdown
Temperament Match: semi-aggressive + peaceful. Semi-aggressive → watch territory and feeding.
⚠️ Size Predation Risk: Swordtail (5.0") vs Threadfin Butterflyfish (8.0"). A 3.0" 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: 30/100 (GOOD ≥80, CAUTION ≥50, RISKY <50).
🔧 Tank Setup Requirements (for Both)
- Minimum tank: 75 gallons — sized for the larger fish in the pair.
- Temperature: keep it between 74°F and 78°F.
- pH: no shared range. One species will be outside its tolerance regardless of what you set.
- Hiding spots: essential for Swordtail — 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 75+ gallons:
Frozen mysis shrimp for marine butterflyfish
Explore Related Checks
See what else works with these fish:
Accuracy note: This tool uses expert rules + FishBase.org data. Individual fish behavior varies — a semi-aggressive individual Swordtail 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.