Japanese Koi Tattoo

The Japanese Koi Tattoo Picture is courtesy of pupatattoo

Female Koi grow larger than male Koi

The reason for that is the human breeders technique.

The best Koi breeding results will be achieved if one female Koi will breed with a group of Koi males, in order to get a variety of different colors and patterns, better immune systems and genetics.
A female with a group of large males that could heart her is not such good idea but a large female with smaller males will make it easier for her to keep good health.
A beautiful large breeding female koi, is very expansive, and Japanese Koi breeders wish, is to keep her safe.
As long as this process repeats the results will continue to be smaller males.