Those things are parasites, and they spread all around with this "herpes like" shape. If i dont remember badly they´re some sort of copepods/crustaceans (dont know the word in english). Mine treated herself by jumping out of the water, just like SW rays. Some Vets recomend Luferunon (Program-Novartis). Use UV to brake the life cycle at the egg stage. Worked for me.