Strange Bone protrusion over Operculum

[Reza]

Dear Guys,

Hope you stay safe and well.
Please check the attached photo, several fish in my pond have such protrusion over their gill cover, over one or both sides.

it is very hard and bony.

Do you friends ever had seen such a problem?
I will be appreciated if you share your knowledge and advice.

[Brian]

Hello Reza,

Is your pond made of concrete or a rough material?

[Reza]

Hello Reza,

Is your pond made of concrete or a rough material?

Dear Brian,

Yes, all of my ponds are concrete but the outdoor ponds are concrete with permanent washing and algae removed from walls.

[Brian]

I see scrapes like these on koi kept in concrete ponds. The photo is kind of small so hard to tell, but is it possible it's just a scrape that's healed and become more bony due to healing?