I don't know what the name of this is, but I DO NOT THINK IT IS HIKKUI! I have seen this twice before this and ONLY THIS YEAR within the last three months. One fish is one of my Sanke and the other belongs to a fellow club member. His fish is only three years old. Mine is going on 5 yrs old.
Hikkui presents more like a flattish blister and usually has some color to it. What you see here are actually like gas bubbles in the epidermis. The other two fish mentioned above had several of these "bubbles" with a lot on the beni plates, but also on the shiroji. I believe, though it can't be proven, that Hikkui is a type of virus(?) and this appears more like a bacterial infection or gas exchange problem from internal to exterior of the fish.
JR, you around to help out with this?
I treated mine with mercurochrome and gave it a shot of Amycacin. It has helped, but one of the areas on the top mid-section next to the dorsal had become infected and scales were raised. These too were swabbed/cleaned with mercurochrome and seem to be doing quite a bit better. This area had no beni on it!
Mike