I am able to expand this picture. From the looks of raised scaled and oval pattern, fish appears to have uronema which is Not uncommon with this fish. Uronema is an oval ciliated motile protozoan which causes tissue necrosis as seen on fish. What other fish are in the tank?
This can also be triggered by low salinity levels as well as excess food waste on tank bottom which this protozoan can feed on as often prevention can be more valuable than cure for this.
Fish will have to be quarantined and treated with formalin based treatment which is harder to find, so next option is Ruby rally Pro. Chloroquine Phosphate will also work but must be used precisely. Uronema is not an obligate parasite, and can thrive on bacteria, uneaten food, and waste so besides treatment also maintain a clean tank removing waste daily.
What other fish are in the tank?