What are the salt-like spots on my fish?

The spots you see are most likely the organism called ichthyophthirius multifilis or ich.  It is a parasite that burrows itself into the skin of fish.  Sometimes because of irritation, fish will rub their bodies along rocks or ornaments.  This disease is very common and easily treated.  The sooner you treat it, the better.  Medication, increasing the water temperature and performing partial water changes are all crucial in killing this parasite.