Looks like Mycobacterium bacteria. these appear as Skin lesions, emaciation,, scale loss, frayed fins and loss of appetite are all signs of this infection. This bacteria are transmitted bi infection, detritus, and feces of the infected fish. They can also create skin wounds and lesions.
The best treatment is prevention and good water quality. Try not to feed raw food to your saltwater fish. Treatment with Antibiotics include kanamyacin, or erythromycin. begin with a good water change.
What is your salinity and tank temperature as well as ammonia and nitrate readings?
