yeah it probabl body fungus which is caused from unhealthy conditions in the tank and also because it could be getting bullied from other fish. if you are to cure the fish you have to act quick and get medication not 100% sure what chemicals so you might have to search it up or ask your local fish shop
the red spots on the belly might be red spot which is often triggered by poor water conditions and from decomposing debris. not sure if there is a cure
so if you are able to just do a water change weekly around 20-30% of the water changed