There was a guy who knew a BUNCH about clownfish, I wonder whatever
happened to him :P

Chrissy, its Lymphocystis, hence the culliflower looking tumor attached to the gill. It is a viral infection transmitted by direct contact with infected fish and can affect any fish, but clownfish are very suseptible to it. It is an "external" virus, so it wont affect any internal organs.. Unfortunetly there is no treatment for lymph... but secondary infections will need to be treated accordingly. The "tumor" may fall of or can be removed by hand if its big enough, although there is a huge chance it may come back, and at times, it just doesnt. Stress in fish can maximize the chances of the virus to attack...So if you've seen any agression in your tank, that could have been the reason that triggered the lymph. (sort of like ich when the immune system is down due to stress)..Try to minmize any stress in the tank (i.e any fish chasing other)..Hope this helps.

(Poof, disappears!).