Koi and Swordtail Compatibility Overview
Koi and Swordtail are generally not recommended to be housed together. Koi is a cool-water fish and Swordtail is tropical, so the usable temperature range decides this pairing. The adult size gap creates a meaningful predation risk. Review the behavior and water details before deciding whether to attempt the pairing.
| Factor | Koi | Swordtail | Verdict |
|---|---|---|---|
| Temperature | 50โ75ยฐF | 65โ80ยฐF | โ 65โ75ยฐF |
| pH Range | 7.0โ8.5 | 7.0โ8.3 | โ 7.0โ8.3 |
| Temperament | peaceful | peaceful | โ Compatible |
| Adult Size | 24 in | 5 in | โ 5ร difference |
| Min. Group | 2+ | 3+ | See below |
| Min. Tank Size | 100 gallons (for both species) | โ | |
Compatibility Positives
Incompatibility Reasons
Species Profiles
Koi โ Cyprinus rubrofuscus
Large pond fish that require hundreds of gallons and cool water. Will eat any fish small enough to fit in their mouth.
Swordtail โ Xiphophorus hellerii
Hardy livebearer with a distinctive elongated lower tail fin in males. Peaceful community fish that tolerate a wide temperature range.
Frequently Asked Questions
Can Koi live with Swordtail?
Generally not recommended. Koi and Swordtail are generally not recommended to be housed together. Koi is a cool-water fish and Swordtail is tropical, so the usable temperature range decides this pairing. The adult size gap creates a meaningful predation risk. Review the behavior and water details before deciding whether to attempt the pairing.
What tank size do I need for Koi and Swordtail together?
A minimum of 100 gallons is recommended for keeping Koi and Swordtail together. A larger tank improves water stability and reduces territorial conflict.
What temperature suits both Koi and Swordtail?
65โ75ยฐF โ inside Koi's 50โ75ยฐF and Swordtail's 65โ80ยฐF.
Is a Koi aggressive toward a Swordtail?
The adult size gap creates a meaningful predation risk.
Related Compatibility Guides
Tank Size for Koi and Swordtail
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. |