If Darwinists insist on describing the changes occurring in the common carp (Cyprinus carpio) as evolution, then it certainly is not of the Darwinian variety.
In Medieval Europe monks selectively bred carp that had fewer scales so the fish would be easier to prepare and cook.
While monks might not have been too fond of scales, fish need them as they protect them from parasites.
Some of these so-called mirrow carp were eventually set free in Madagascar in 1912.
A paper published in the Proceedings of the Royal Society B shows that while the carp had a loss-of-function mutation resulting in “reduced scale cover”, they are now mostly covered with scales.
It seems that the environment helped them to regain something they once had. Nothing new is introduced; no evolution is occurring.