What are your water parameters? Ammonia, Nitrite and Nitrate? pH, anything else?
It looks like pine cone disease, usually poor water conditions.
Do you use a water treatment like a dechlorinator / heavy metals binder?
Size of tank?
How often and how much water do you change?
How long has your tank been set up and do you know if it is cycled?
If you are a little bit new to keeping fish check out the link which is an article for new tanks and learning about keeping fish. There are other articles which might help you get some basics for freshwater fish keeping.
That fish is likely to pass away from the looks of it.
Do you know your water quality out of the faucet?
When was the last pwc and how much?
I would likely do 2 50% back to back water changes using temperature matched, and treated water. The reason is for making the new water change gradual so new water doesn't shock the fish.