Well if it is a fungal infection ketoconazole should clear it up.
http://www.healthypets.com/fifuk2030ta.html
It doesn't look like a fungal infection to me though. I looked through my Noga fish disease book and couldn't find anything that really fit exactly. If I had to guess I would say some type of myxozoan infection, which is not treatable. That would fit well with what the marine biologist guy said. Here's a google.books link to Noga's description of myxozoan infections...
http://books.google.com/books?id=SA...0CBQQ6AEwAA#v=onepage&q=myxozoan noga&f=false
http://www.healthypets.com/fifuk2030ta.html
It doesn't look like a fungal infection to me though. I looked through my Noga fish disease book and couldn't find anything that really fit exactly. If I had to guess I would say some type of myxozoan infection, which is not treatable. That would fit well with what the marine biologist guy said. Here's a google.books link to Noga's description of myxozoan infections...
http://books.google.com/books?id=SA...0CBQQ6AEwAA#v=onepage&q=myxozoan noga&f=false