It looks like Lymphocystis, I'd suggest looking it up and looking at pics of it to see if that is what you see on him.
Lymphocystis is a virus, and being a virus, it affects the cells of the fish. It usually manifests itself as abnormally large white lumps (cauliflower) on the fins or other parts of the body. It can be infectious, but is usually not fatal. Unfortunately there is no cure.
Lymphocystis is not as common as fish diseases and conditions like ich and fungal infections, but once introduced into an aquarium it can rapidly become a problem thanks to its high rate of infection. This disease, unlike many of the more common aquarium ailments, is not caused by organisms that may commonly be found in aquaria. The virus that causes Lymphocystis can be introduced only via fish that are already infected or water, décor, gravel, rocks or plants sourced from infected areas. This makes pre-treatment of newly purchased fish vital to prevent Lymphocystis, as well as activities geared to ensure that introduced plants and other rocks and other objects are not simply placed in without making sure that they are cleaned.
The virus that causes Lymphocystis infects fish fin and skin cells and causes them to enlarge significantly. At the outset of the infection, the infected cells may appear as white pinpricks - very similar to ich and other such diseases, thu making proper diagnosis difficult. However, as time goes on, these cells may enlarge and/or clump together to form nodules, lesions or lumps that can be larger than two millimeters in diameter. At the end part of this stage - which usually occurs in about the fourth week of infection - the engorged cells burst and the material inside them is released into the aquarium water. From there it can also proceed to infect other unfortunate fish. The host tissue of the initial sufferers then returns to normal size and condition and is free to heal.
But I could be wrong.. just looks like it to me.