Lymphocystis typically is seen on the fins on saltwater fish although it is not uncommon to see growths on the skin as well. However the infection tends to start on the fins.
There are arguments by many that there no cure for Lymph. I have never cured it. I have been able to control the growths by trimming the fins using iodine on the fin after the "surgery".
I am not an expert on identifying illness. In fact many illnesses in regards to fish are misdiagnosed. Cultures and scrapings under a microscope (and an educated knowledge base) is the only way to truly diagnose. Ick, well thats an easy one. IMHO I dont think it is Lymph... I believe it is protazoal...
Is there a coating or film on the fish. Bite Marks? Are they scratching, breathing heavy? Are they Eating? Are they wild caught or captive raised.
Clownfish are very prone to being infected with "Clownfish Disease" or Brooklynella . At the onset fish may scrap up against objects, rapid respiration develops, and fish often gasp for air at the surface as the gills become clogged with mucus. Fish become lethargic, refuse to eat, and colors fade, but the most noticeable difference that sets Brooklynella apart from Oodinium is the heavy amount of slime that is produced. As the disease progresses a thick whitish mucus covers the body, usually starting at the head and spreading outward, skin lesions appear, and it is not uncommon for signs of secondary bacterial infections to arise.
If it is the store should be called and pics sent..... Nasty affliction.....