Koi fish typically live between 25 to 50 years on average when kept in proper environmental conditions, including good water quality, nutrition, and health care

. Japanese koi tend to live longer, with an average lifespan around 40 years, compared to about 15 years for koi bred outside Japan, due to differences in genetics, diet, and care practices

. There are exceptional cases where koi have lived significantly longer. The oldest koi ever documented was a Japanese koi named Hanako, reportedly living to 226 years old, although this extreme longevity is disputed and considered by some as more legend than verified fact

. In summary:

• Average koi lifespan: 25–50 years
• Japanese koi average: ~40 years
• Non-Japanese koi average: ~15 years
• Exceptional longevity: up to 200+ years (unverified)

Proper care, including maintaining water quality, balanced feeding, and veterinary care, is crucial to achieving the upper range of koi lifespan