Compatibility Overview
Harlequin Rasbora and Lionfish are generally not recommended to be housed together. The issues listed above — whether water parameter incompatibility, predation risk, or aggression — create conditions where one or both fish are likely to suffer harm or chronic stress.
| Factor | Harlequin Rasbora | Lionfish | Verdict |
|---|---|---|---|
| Temperature | 72–81°F | 72–82°F | ✅ 72–81°F |
| pH Range | 5.5–7.5 | 8.1–8.4 | ❌ No overlap |
| Temperament | peaceful | aggressive | ❌ Risk |
| Adult Size | 1.75 in | 3.1 in | ✅ Similar |
| Min. Group | 8+ | 1+ | See below |
| Min. Tank Size | 55 gallons (for both species) | — | |
✅ Compatibility Positives
❌ Incompatibility Reasons
Species Profiles
Harlequin Rasbora — Trigonostigma heteromorpha
Active mid-level schooling fish with a distinctive black triangular patch. One of the best all-around community tank fish.
→ Full Harlequin Rasbora care guide
Lionfish — Aquarium species
Lionfish are popular saltwater aquarium fish known for their striking colors and intimidating spines. These fish require a large tank and careful attention to water parameters. Aggressive by nature, they can be harmful to smaller fish and invertebrates.
Frequently Asked Questions
Can Harlequin Rasbora live with Lionfish?
Generally not recommended. Harlequin Rasbora and Lionfish are generally not recommended to be housed together. The issues listed above — whether water parameter incompatibility, predation risk, or aggression — create conditions where one or both fish are likely to suffer harm or chronic stress.
What tank size do I need for Harlequin Rasbora and Lionfish together?
A minimum of 55 gallons is recommended for keeping Harlequin Rasbora and Lionfish together. A larger tank improves water stability and reduces territorial conflict.
What temperature suits both Harlequin Rasbora and Lionfish?
72–81°F
Is a Harlequin Rasbora aggressive toward a Lionfish?
Harlequin Rasbora is peaceful and Lionfish is aggressive. These animals require different water types and cannot share one aquarium.
Related Compatibility Guides
Compatibility score breakdown
The overall score is weighted across water chemistry, behavior, adult size, swimming zone, and social needs. A score is a planning aid—not a guarantee for individual fish.
| Factor | Score |
|---|---|
| Temperature | 100/100 |
| Ph | 0/100 |
| Temperament | 30/100 |
| Adult Size | 100/100 |
| Swim Zone | 68/100 |
| Social Needs | 92/100 |
Tank size scenarios
Use the scenario that matches the actual group sizes and temperament you plan to keep.
| Scenario | Tank | When it applies |
|---|---|---|
| Minimum viable | 264 gal | Only for the recommended minimum groups, mature filtration, and close monitoring. |
| Recommended community | 400 gal | Adds territory, swimming room, and a safer buffer for behavior. |
| Low-conflict setup | 500 gal | Best when keeping larger schools or reducing territorial pressure. |