Can Hillstream Loach live with Threadfin Butterflyfish?
High risk due to water mismatch, aggression, or predation.
Why Hillstream Loach and Threadfin Butterflyfish Don't Make an Easy Pair
The size gap is 5.5" — Hillstream Loach (2.5") and Threadfin Butterflyfish (8.0"). A fish that fits in another fish's mouth will eventually end up there.
Hillstream Loach
Sewellia lineolata
| Adult Size: | 2.5" |
| Temperament: | peaceful |
| Min Tank: | 20 gal |
| Temperature: | 64-75°F |
| pH Range: | 6.5-7.5 |
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 | Hillstream Loach | Threadfin Butterflyfish | Overlap |
|---|---|---|---|
| Temperature | 64-75°F | 74-82°F | 1°F ✓ |
| pH | 6.5-7.5 | 8.1-8.4 | No overlap ✗ |
Compatibility Breakdown
Temperament Match: peaceful + peaceful. Both peaceful → minimal conflict.
⚠️ Size Predation Risk: Hillstream Loach (2.5") vs Threadfin Butterflyfish (8.0"). A 5.5" 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: 10/100 (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 75°F.
- pH: no shared range. One species will be outside its tolerance regardless of what you set.
- Hiding spots: essential for Hillstream Loach — 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
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Accuracy note: This tool uses expert rules + FishBase.org data. Individual fish behavior varies — a peaceful individual Hillstream Loach 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.