Bumps/traumas, run ins with spiny, stinging tankmates, subsequent reaction/s to netting, shipping, handling, captive stress. Unless these are numerous, such spots rarely portend pathogenic disease, though sometimes are indicative of encysted worms or microsporideans.
Improved environment and nutrition; anthelminthic and anti-protozoals if indicated. Adding Cleaner Organism/s may help. (get a cleaner shrimp).