Can Oscar live with Swordtail?
High risk due to water mismatch, aggression, or predation.
Why Oscar and Swordtail Don't Make an Easy Pair
The size gap is 7.0" — Oscar (12.0") and Swordtail (5.0"). A fish that fits in another fish's mouth will eventually end up there.
Oscar
Astronotus ocellatus
| Adult Size: | 12.0" |
| Temperament: | aggressive |
| Min Tank: | 75 gal |
| Temperature: | 74-81°F |
| pH Range: | 6.0-7.5 |
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 | Oscar | Swordtail | Overlap |
|---|---|---|---|
| Temperature | 74-81°F | 72-78°F | 4°F ✓ |
| pH | 6.0-7.5 | 7.0-8.0 | 0.5 ✓ |
Compatibility Breakdown
Temperament Match: aggressive + semi-aggressive. One aggressive → predation/nipping risk.
⚠️ Size Predation Risk: Oscar (12.0") vs Swordtail (5.0"). A 7.0" 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: 25.0/100 (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: maintain 7.0 – 7.5.
- 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:
High-capacity canister filter for oscar tanks
Explore Related Checks
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Accuracy note: This tool uses expert rules + FishBase.org data. Individual fish behavior varies — a aggressive individual Oscar 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.