Compatibility Overview
Koi and Rosy Barb 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 | Koi | Rosy Barb | Verdict |
|---|---|---|---|
| Temperature | 50–75°F | 72–82°F | ⚠️ 72–75°F (narrow) |
| pH Range | 7.0–8.5 | 6.5–7.5 | ⚠️ 7.0–7.5 (narrow) |
| Temperament | peaceful | semi | ⚠️ Monitor |
| Adult Size | 24 in | 2.0 in | ❌ 12× difference |
| Min. Group | 2+ | 1+ | See below |
| Min. Tank Size | 100 gallons (for both species) | — | |
✅ Compatibility Positives
❌ Incompatibility Reasons
Species Profiles
Koi — Cyprinus rubrofuscus
Large pond fish that require hundreds of gallons and cool water. Will eat any fish small enough to fit in their mouth.
Rosy Barb — Aquarium species
The Rosy Barb is a popular freshwater fish known for its vibrant coloration and peaceful nature. It is well-suited for community tanks with other non-aggressive species. They require a well-maintained environment and can be sensitive to water quality fluctuations. With proper care, they can thrive and add a splash of color to your aquarium.
Frequently Asked Questions
Can Koi live with Rosy Barb?
Generally not recommended. Koi and Rosy Barb 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 Koi and Rosy Barb together?
A minimum of 100 gallons is recommended for keeping Koi and Rosy Barb together. A larger tank improves water stability and reduces territorial conflict.
What temperature suits both Koi and Rosy Barb?
72–75°F (narrow)
Is a Koi aggressive toward a Rosy Barb?
Koi is peaceful and Rosy Barb is semi. 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 | 30/100 |
| Ph | 50/100 |
| Temperament | 75/100 |
| Adult Size | 8/100 |
| 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 | 100 gal | Only for the recommended minimum groups, mature filtration, and close monitoring. |
| Recommended community | 150 gal | Adds territory, swimming room, and a safer buffer for behavior. |
| Low-conflict setup | 180 gal | Best when keeping larger schools or reducing territorial pressure. |