How to Differentiate Male and Female Koi

If you are a new koi owner or breeder, the first thing you would probably want to know is how to tell whether a koi fish is male or female. This task might seem daunting at first, but knowing the differences between the male and female koi fish will make sex identification a breeze. Here are the differences that you should take into consideration.

  1. Size and shape. The male koi fish is slender and shaped like a torpedo. The female koi, on the other hand, are considerably fatter around the abdominal are. They are also wider and rounder in shape. While this characteristic is usually sufficient in identifying the sex of the koi, you need to consider other factors as well, such as the koi diet, its genes, and various other environmental factors. These can affect the size and the body shape of the koi fish. As such, this factor may not always be accurate.
  2. Fins. Observing the shape and size of the fins of the koi fish can also help in determining whether it is male or female. The female koi fish has a generally larger fin. However, its fins will have fewer colors and a more rounded shape. On the other hand, the fin of the male koi fish tends to be sharper rather than rounded on the edges. It will also have a comparatively more solid color.
  3. Excretion hole. There is also a difference between the excretion holes of the male and female koi. In the female koi, the excretion hole will be more prominent, with a pale pinkish color, while in the male koi, the excretion hole will be more sunken. The color is white rather than pale pink.
  4. Cheek surface. The cheek surface of the male and the female koi also differs. The female koi will have smooth cheeks. The male koi, will have a rough cheek surface.
  5. Tubercles. During breeding time, it will be much easier to identify the sex of your koi fish. Male koi fish will start developing tubercles or white spots. These small spots will be highly concentrated around the gill plates and should be easy to spot.
  6. Breeding time. The most obvious indication, of course, will be observed around breeding time. Obviously, the fish that will spawn and lay eggs will be the females. You will also observe that the male koi will chase a female koi during this time (this would basically be the equivalent of courting for koi fish). If you ever spot a koi fish bumping the back end or the side of another koi fish, chances are, the one doing the bumping will be a male koi.

Please note that the differences between the male and female koi fish will only start to become evident once they are old enough. If you are not sure whether the koi you intend to purchase is male or female, it pays to ask the seller directly.