How To Identify The Gender Of Koi Fish

Thought to have originated in China, koi fish have mainly been bred in Japan for their aesthetic appeal since the mid 1800’s. With each variety of the fish coming different colors, with most popular being the Kohaku and the Taisho breed. In ideal conditions koi fish have been known to grow up to three feet long, with females usually larger than males. For a breeder, prices for highly sought after koi can range in the thousands if not more. Such prices can lure even the average koi owner to start breeding but in order to start this process, can you even tell the difference between a male and a female? We have shared some advice below as to how you can determine the age and gender of your koi fish.

Age Of Your Koi

Koi can be easier to tell apart once they are mature. The length of your koi will play a huge part in determining the age. Usually once they are around ten inches long their age is deemed to be three years and are considered mature. Any shorter than ten inches, they are still considered juveniles.

The Shape Of Its Body

Capturing your koi with a fish net and taking a look at it body, you will notice that a male generally has slender look to it. A female on the other hand will have a more rounded body, this will be more evident if she is carrying a nest full of eggs during spawning season.

Shape Of Their Fins

Examining your koi’s fins, you will notice that one has a more pointed pectoral fin near the head which is solid in color, this indicates a male koi. Females will have a mostly rounded fin compared to the male.

Tubercles In Males

While breeding season is in full swing the male koi may produce small white growths on their heads and pectoral fins, this is known as tubercles. These growths are natural during the breeding season for males and will almost certainly disappear once the season is over, do not be alarmed by these growths as it is no risk to their health. Female on the other hand will not get such growths on there body during this time, another sign of which gender you have swimming in your tank.

Their Behavior

Our last bit of advice can be the behavior of your koi. Whilst not in breeding season your koi will generally behave just as normal but as soon as the season approaches you can expect the male koi to start chasing the females around, enticing her to release her eggs so he can then fertilize them. Such a change in behavior will become obvious to the owner during this time, with the excited koi then calming down once their mission is complete! These tips should help you in determining the gender of your koi fish. Happy breeding!