koi have hardly faded skin and show attenuated melanophore sensitivity to adrenaline and melanin-concentrating hormone.

Introduction: Koi carp, an ornamental fish derived from the common carp (CC), is characterized by beautiful skin color patterns. However, the mechanism that gives rise to the characteristic vivid skin coloration of koi carp has not been clarified. The skin coloration of many teleosts changes in response to differences in the background color.