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Family name Koi (Koi
, 開
, Кой
) , globally, is a common last name. The family name Koi is habitual in Fiji, where it is quite a common surname, Papua New Guinea, and Malaysia, where it is quite a rare surname. Measured by absolute frequency, it is the most numerous in China, Malaysia, and Indonesia. Likewise, Koi is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| Koi | Malaysia, India, Japan, Indonesia, Kenya |
| 開 | China |
| Кой | Kazakhstan, Kyrgyzstan, Russia, Ukraine |
| Кои | Russia |