Harlequin Rasbora and Koi Compatibility Overview
Harlequin Rasbora and Koi are generally not recommended to be housed together. Koi is a cool-water fish and Harlequin Rasbora 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 | Harlequin Rasbora | Koi | Verdict |
|---|---|---|---|
| Temperature | 72โ81ยฐF | 50โ75ยฐF | โ ๏ธ 72โ75ยฐF (narrow) |
| pH Range | 5.5โ7.5 | 7.0โ8.5 | โ ๏ธ 7.0โ7.5 (narrow) |
| Temperament | peaceful | peaceful | โ Compatible |
| Adult Size | 1.75 in | 24 in | โ 14ร difference |
| Min. Group | 8+ | 2+ | See below |
| Min. Tank Size | 100 gallons (for both species) | โ | |
Compatibility Positives
Incompatibility Reasons
Species Profiles
Harlequin Rasbora โ Trigonostigma heteromorpha
Active mid-level schooling fish with a distinctive black triangular patch. One of the best all-around community tank fish.
โ Full Harlequin Rasbora care guide
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.
Frequently Asked Questions
Can Harlequin Rasbora live with Koi?
Generally not recommended. Harlequin Rasbora and Koi are generally not recommended to be housed together. Koi is a cool-water fish and Harlequin Rasbora 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 Harlequin Rasbora and Koi together?
A minimum of 100 gallons is recommended for keeping Harlequin Rasbora and Koi together. A larger tank improves water stability and reduces territorial conflict.
What temperature suits both Harlequin Rasbora and Koi?
72โ75ยฐF (narrow) โ inside Harlequin Rasbora's 72โ81ยฐF and Koi's 50โ75ยฐF.
Is a Harlequin Rasbora aggressive toward a Koi?
The adult size gap creates a meaningful predation risk.
Related Compatibility Guides
Tank Size for Harlequin Rasbora and Koi
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 | 220 gal | Best when keeping larger schools or reducing territorial pressure. |