Tengbells the good news is there isnt anything wrong with this koi judging from your second lot of photographs all is well
OK what is Hiku or Hi-kui well it is a disease that attacks the red pigmentation in our koi in Japanese that is what it also translates too.."A disease that causes a loss of red pigmentation"!!!!.....
It will normally show itself as small areas of discolouration in the red areas of the koi's pigmentation , the red will look faded compared to the rest of the red on the koi .
Second an area of pigmentation will take on a brownish haze , thirdly small dark brown areas may apear from pinhead size to that of a small US in your case coin now whatever my descriptions you'll also notice a thickening of the overlying epidermal tissue of your koi
Trigger factors an over exposure to sunlight being the most likely because excessive sunlight can cause small tumours of the red pigment cells damaging the koi's DNA .
Secondly poor maintenance of the pond and its systems can cause attacks of Hi-Kui to become worse as waste and detritus in the system can attract anaerobic bacteria, which will view these otherwise affected areas as an ideal site to settle and cause secondary infections which we dont want
.
Prevention of this is obvious with good healthy maintenance this stage can be avioded , I wont go into the treatment with scalpel's to remove it as I'm not abig believer in cosmetic surgery on koi
Dave
