Is Your Koi A Boy? Or A Girl?

Is Your Koi A Boy? Or A Girl?

Is Your Koi A Boy? Or A Girl?

The easiest way to identify the gender of koi fishes is to ask the breeder about it.

Believe me, they will have an answer.

But, of course, it wouldn’t hurt to know the basics of the gender of koi fish identification, especially if you intend to later breed koi fishes yourself.

So without further ado, here’s everything you need to know about gender of koi identification.

Koi Fish Gender Identification 101

As with other animals, there are certain signs or factors which you should look at for accurate gender of koi


Here are the things which will help you differentiate between male and female koi fishes:

Gender of Koi

Koi Size

This one is tricky because you have to consider the age of the koi before using size to determine the gender of koi fish.

When it comes to young koi, male koi fishes are generally larger than their female counterparts.

However, when it comes to mature koi, male koi fishes tend to be smaller and slimmer.

Koi Body Shape

If you’re looking at mature koi fishes, then body shape is another easy way of determining which ones are males and which ones are females.

Male koi fishes have slender bodies.

On the other hand, female koi fishes have broader shoulders and fuller, rounder bodies.

This is especially the case when the female koi fishes are spawning.

Koi Fin Shape

Aside from size and body shape, there are also significant differences between male and female koi fishes in terms of appearance of their fins.

While the male koi fish’s pectoral fins are pointed and have a solid color, the pectoral fins of female koi fishes usually appear rounder.

Koi Pelvic Bones

You can also try feeling the pelvic bones of your mature koi fishes to determine its gender.

Female koi fishes have a soft abdomen in between the bones.

Male koi fishes don’t have soft abdomens since their bones are fused.

Gender Of Koi

Eating Behaviour Your Koi

You might find this surprising but female koi fishes are actually more aggressive when it comes to eating compared to male koi fishes.

Female koi fishes tend to stay near the surface and eat continually during feeding, while the males will tend to swim around.

Koi Tubercles

The differences between male and female koi fishes increase during mating season.

You will notice that during breeding season, little white growths (these are called tubercles) will begin to appear on the heads and pectoral fins of male koi fishes.

These white growths are exclusive to male koi fishes and will eventually disappear once the mating season is over.

Koi Mating Behavior

During breeding season, you will notice that male koi fishes will pursue the female koi fishes.

Note however that this amorous behavior on the male koi’s part is limited to breeding seasons.

The difficulty with differentiating male and female koi fishes lies in the fact that unlike peacocks, both male and female koi are very decorative.

This is why the most reliable factors for the gender of koi fish identification are the factors above.

New Koi Fish to add to your Pond? Maybe a Butterfly Koi?What about a Kohaku Koi?

What other breeds are out there? Check this article out then: Discovering The Different Varieties Of Koi Fish

Don’t have a Pond? How about Building your Own? Here are the most important things to remember when building a koi pond

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