The Black Moor Goldfish is Telescope Goldfish black variety. The eyes are less prominent than the telescope. They can live at temperatures very old, making it ideal for outdoor ponds. Care should be taken with his bulging eyes that are not damaged. Be careful what type of decoration is added to the tank so that your eyes will not get scratched in a plant with a sharp plastic sheets. It begins as a black velvet and can be a bit gray as they age. All variations of ornamental varieties, such as the Black Moor, Bubble Veil-tails, eyes, praying, etc., are all strains developed through selective breeding, and do not occur in nature in that form naturally.

Is the black sore a bump or a crater or is it just a mark? It's hard to tell from the photo. Are there any other symptoms? What is your water quality like? Have you tested for ammonia, nitrate and nitrite?

Hmmm...maybe he's going to turn black again, starting with a small spot on his eye? Sorry, i have no idea. Maybe you could treat the tank with a general bacterial/fungal medication. It would be a shot in the dark, but those treatments tend to be quite safe.