Red pectoral fin
Yellow tang has a blood red pectoral spot in the flesh where the fin joins.
There is no ulcer (skin is closed). I would say it's not trauma because it's on the upper side of the fin which is pretty well protected by the fin and the fin it's self has no damage. I did treat for a fungus about a week ago. Every fish has looked fine since.
Anyone ever encountered and if so can u share Ur outcome