How to determine the sex of your Koi

Without the right knowledge determining the sex of your koi can be confusing. Fortunately deciphering whether your fish is male or female really isn’t that difficult. However, it is easier to find out when your fish are about 2 years old and have grown out a little.

The most reliable way to determine the sex of your Koi is by taking a close look at the fins, look for shape and color. Males generally have smaller pointed fins and the fins are opaque with colors in them. Females have larger more rounded fins that are translucent or even transparent and can be completely absent of color. These differences are the same even in Butterfly (also known as long fin) Koi.

Male Koi Fin

Male Koi Fin


Female Koi Fin

Female Koi Fin

The second way to determine the sex of your Koi is by looking at how the body is shaped. This method is a little less accurate than the fin method but still works. Males are relatively long and slender because their bodies do not need to accommodate eggs. After females reach 2 years of age their bodies start to develop eggs and this widens their bodies making a noticeable difference this effect is exaggerated during the fishes spawning season giving them a blimp like appearance. Also females tend to grow larger than the males due to the extensive selective breeding they have gone through.

Female Koi Body shape

Female Koi Body shape


Male Koi Body shape

Male Koi Body shape

Leave a Reply