Sorry about your fish. What size tank and what other fish are in there? Have you noticed any aggression? Is it a new tank? Is it cycled? What are your water parameters (ammonia, nitrite, nitrate) just to eliminate water quality as an issue.
He looks very battered, but it's hard to tell whether its' a fungus or an injury. You could quarantine him and keep his water very clean for a few days (put a heater and an air stone in the quarantine tank if you have one) and see if it starts to heal. If not you may need to consider some aquarium salt and/or medications but I'm not the best person to suggest which to use. Hopefully someone else can help further.
