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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).