wowsza... that is some big carp. The colour of a carp is generally governed by pigment cells in the skin of the fish. These are called chromatophores and most are black but other colours do exist. These contract or expand to make a fish either lighter or darker respectively. This process is relulated by hormones in the fish's blood."

And did you know there is such a thing as Carpology? https://www.carpology.net/article/featu ... e-colour-/