It’s been a while since I caught a sick one. I guess it might be a result of the pond level being 20” low and very little new water coming in.

FWIW, the next 4 I caught were clean.

Could be thermal shock from recent cold, especially if the fish was shallow spawner when cold hit. In 2017 I lost hundreds of my larger CNBG after sharp cold October snap. Keep a lookout for this, I think some here have recommended treating feed with antibiotic.

Maybe adding some kosher salt could be a bit of a boost for some of these fish...

Oy Vey!!!

Not something you want to try, or bad experience with it?

Myxosporidia?

http://outdoornebraska.gov/wp-content/uploads/2015/11/PMGS_Fish_Parasites_Diseases.pdf

Shorty may be correct.

Since snails are a part of the life cycle of several of the common parasites, do you have RES in your pond?

Are all those imperfections in the photo the little yellow grubs?

They look like fish lice to me.

I've only ever seen yellow grubs inside of fish - YMMV.