Color fading, or the loss of red pigmentation, is a common occurrence in koi keeping. Numerous factors can cause it, with genetic lineage being a significant and influential one. Other contributing factors include treatments for illness (such as adding salt), stress from water changes, and excessively rapid growth. The root cause lies in the koi's inability to synthesize carotenoids, the primary component of their red coloration. Koi must obtain these pigments from their diet or the water environment.
Therefore, if disease, stress, changes in water quality, or osmotic pressure imbalance reduce or block the absorption of carotenoids, or if the intake cannot meet the demands of accelerated growth, it will ultimately result in the fading of the koi's red color.
