Can Goldfish live with Red Tail Black Shark?
High risk due to water mismatch, aggression, or predation.
Why Goldfish and Red Tail Black Shark Don't Make an Easy Pair
The size gap is 5.0" — Goldfish (10.0") and Red Tail Black Shark (5.0"). A fish that fits in another fish's mouth will eventually end up there.
Goldfish
Carassius auratus
| Adult Size: | 10.0" |
| Temperament: | peaceful |
| Min Tank: | 30 gal |
| Temperature: | 62-74°F |
| pH Range: | 6.5-7.5 |
Red Tail Black Shark
Epalzeorhynchos bicolor
| Adult Size: | 5.0" |
| Temperament: | semi-aggressive |
| Min Tank: | 30 gal |
| Temperature: | 72-80°F |
| pH Range: | 6.5-7.5 |
Water Parameter Overlap
| Parameter | Goldfish | Red Tail Black Shark | Overlap |
|---|---|---|---|
| Temperature | 62-74°F | 72-80°F | 2°F ✓ |
| pH | 6.5-7.5 | 6.5-7.5 | 1.0 ✓ |
Compatibility Breakdown
Temperament Match: peaceful + semi-aggressive. Semi-aggressive → watch territory and feeding.
⚠️ Size Predation Risk: Goldfish (10.0") vs Red Tail Black Shark (5.0"). A 5.0" gap — the larger fish will view the smaller fish as food.
Score: 30.0/100 (GOOD ≥80, CAUTION ≥50, RISKY <50).
🔧 Tank Setup Requirements (for Both)
- Minimum tank: 30 gallons — sized for the larger fish in the pair.
- Temperature: keep it between 72°F and 74°F.
- pH: maintain 6.5 – 7.5.
- Hiding spots: essential for Goldfish — 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 30+ gallons:
Goldfish-specific flake food
Explore Related Checks
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Accuracy note: This tool uses expert rules + FishBase.org data. Individual fish behavior varies — a peaceful individual Goldfish 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.