Can Betta Fish live with Lawnmower Blenny?
High risk due to water mismatch, aggression, or predation.
Why Betta Fish and Lawnmower Blenny Don't Make an Easy Pair
The size gap is 2.2" — Betta Fish (2.8") and Lawnmower Blenny (5.0"). A fish that fits in another fish's mouth will eventually end up there.
Betta Fish
Betta splendens
| Adult Size: | 2.8" |
| Temperament: | semi-aggressive |
| Min Tank: | 5 gal |
| Temperature: | 75-80°F |
| pH Range: | 6.5-7.5 |
Lawnmower Blenny
Salarias fasciatus
| Adult Size: | 5.0" |
| Temperament: | peaceful |
| Min Tank: | 30 gal |
| Temperature: | 74-82°F |
| pH Range: | 8.1-8.4 |
Water Parameter Overlap
| Parameter | Betta Fish | Lawnmower Blenny | Overlap |
|---|---|---|---|
| Temperature | 75-80°F | 74-82°F | 5°F ✓ |
| pH | 6.5-7.5 | 8.1-8.4 | No overlap ✗ |
Compatibility Breakdown
Temperament Match: semi-aggressive + peaceful. Semi-aggressive → watch territory and feeding.
⚠️ Size Predation Risk: Betta Fish (2.8") vs Lawnmower Blenny (5.0"). A 2.2" 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: 40/100 (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 75°F and 80°F.
- pH: no shared range. One species will be outside its tolerance regardless of what you set.
- Hiding spots: essential for Betta Fish — 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:
Dried seaweed sheets for marine herbivores
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 Betta Fish 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.