Koi tends to grow the fastest during the first two years of its life. In the first year , a koi can grow to a length of seven inches and reach reach twelve inches by the time it's two years old. By its third year , most koi will be around sixteen inches long, which is far too large for most home aquariums. Some individual koi has been known to reach a length of over five feet. The lifespan for a koi can exceed forty years or more. After the first two years , a koi's growth will slow down and it will not reach its full length until around twelve to thirteen years later.
A full grown koi can weigh alot , sometimes exceeding forty five pounds.