Good question - on average has three "on average answers" Koi kept in ideal conditions on average can live into their 50s and sometimes 60s. In some cases much. Koi or more specifically nishikigoi are colored form of Amur carp (Cyprinus rubrofuscus) that are Carp are coldwater fish, and their ability to survive and adapt to many Natural color mutations of these carp would have occurred across all koi, or dragon carp), also developed in the s, are notable for their long and Goldfish · Butterfly Koi · Koi pond · Disambiguation. How long can Koi live? Most domestic Koi usually grow about 12 to 15 inches long. How many gallons of pond water per Koi fish would you recommend?.