This can be caused by the Breeding-activity of the fish ... (fish can, and do act very rough during the spawning process) or of course it could be a parasitic attack having broken the skin and bacteria are starting to infect the areas.

Costia infections may also cause raised areas of scales but a microscopic examination would be required to definitively prove that. 

Instead, you can establish water quality by careful testing and if all that's normal, you'd be wise to treat the fish to a Salt bath at the dosage rate of between7% or 3/4 ounce up to 10% or 1 ounce per gallon, again ensure that you have at least one air stone in the bowl that you are treating the fish in.

Personally, if I had a fish with such a lesion, I'd treat the fish in this manner using a salt bath first then use a good topical dressing such as Koi Doc