Interesting little fish, they have to breathe from the surface.
I am thinking that is a female from the rounded dorsal fin?
A few things:
Is that the natural color (it looks like it has lost some color)?
If so, do you have plants and did you use ferts/meds or other substances?
Have you varied the diet?
Are the light too bright for that fish and does she have shade?
If not, what I stated above may be the problem. It doesn't look like Hole in the head to me, but I could be wrong.
Hopefully one of our better FW
folks can help you better than me.
For the gill stuff, to really ID what is going on requires sample to be checked under a microscope (a good portion of the time).