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Koi Varieties - Why Do Koi Change Colours and Patterns?

You may often notice when keeping koi that the colours and patterns they show when you buy them are not the same as after a year or more. This happens for a variety of reasons and today we will go through the main reasons, and whether you should be concerned.


The first, and main reason is simply genetics. Each fish has a combination of dominant and recessive genes from their parents that determines the colouration and markings that it will show as it grows. For example, a Kohaku will have genes corresponding to a shiroji (white) base colour and hi (red) markings while a Showa will have genes corresponding to sumi (black) base and hi and shiroji markings (red and white, respectively).

Golden Corn Koi Tosai
Golden Corn Tosai

Some koi varieties can change massively throughout their lives, making it difficult to judge a small koi and predict what it will look like as it ages and grows. Take our Golden Corn koi as an example. Our tosai Golden Corn have a bright orange head and very shiny ginrin body but a full sized adult Golden Corn has a deep orange colouration all over with highly defined ginrin scales each with a darker centre.

Shiro Utsuri tosai displaying sumi just under the skin

This is one extreme example, most koi will not change this much over their lifetime and there are often indicators in the juvenile pattern to give you hints about the adult pattern. For example, you may see some young koi with lovely blue markings. This usually is due to a darker black pigmentation under the skin meaning that as the fish ages, the blue markings are likely to become black markings.


The next reason that a fish can change colour is due to its diet. A good, healthy diet with the right vitamins and nutrients to support vibrant colour will result in happy, healthy looking fish with lovely and clear markings and colour distinctions. If a poorer diet is provided to your koi, it can result in your fish looking more watered down and faded with less distinction between the different colours and markings on your koi. A quick and easy way to help the vibrancy of your koi is to introduce oranges and watermelon as these both have natural colour intensifiers for many types of fish.


Another common reason for a koi to look faded and pale is stress, in particular stressful water conditions. Other causes of stress, such as transportation, can cause a koi to lose their colour, but they usually recover quickly in these cases. So, if your koi arrive looking a bit more faded and paler than you were expecting, settle them in to their new home and they should regain their lovely, vibrant colours and markings within a few days!

5 in 1 Water Test Kit
5 in 1 Water Test Kit (NO3, NO2, pH, KH & GH)

Stressful water conditions can include dirty water or a lack of oxygenation. We recommend that you use a suitable filtration system for your setup and regularly check your water quality with a test kit by measuring the amount of ammonia and the pH level of your pond. Also, it is very important that the water you are putting into your ponds is suitable for

fish to be kept in using a de-chlorinator or another method for removing harmful chemicals and minerals. For more information on this topic, see our blog post -

Sunlight Exposure

The final potential reason for a colour change in your koi fish is to do with the amount of sun exposure your fish receive. This is actually rarely noticeable in koi except for when the winter season ends. As your koi will get less exposure to the sun during winter, they may look a bit pale and less vibrant with less distinction between the markings at the beginning of spring. Over the spring season and into summer, however, your koi will quickly brighten up to their normal, healthy, and vibrant colouration. This is quite similar to how we get a tan in the summer from sun exposure but go paler in the winter from less sun exposure.

Koi fish can change colours and markings quite a lot over their lifetime. For some varieties, you may see little changes from juvenile to adult sizes, for others the changes can be quite drastic. A massive part of what makes a koi breeder successful is their ability to predict how the pattern of a particular koi will change over its life. This is never easy, but some koi breeders have an incredibly good eye and consistently produce fantastic grade koi for us to enjoy and share with you.

To have a look at our current stock of koi for sale, click here:

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