It's cauliflower disease (Lymphocystis). Glassfish are very susceptable to it.
I've never had it in any other fish than Parambassis ranga (glassfish). When I bought mine some of them already had it and it eventually cleared up as I raised the salinity in their tank. I notice it'll pop up again if and when the salinity in the tank gets low. I try keeping their water no lower than SG1.004 and keep the water as free of nitrates (with nitrites and ammonia at 0) as possible.
Based on things I've read there is no real "cure" for it as of yet.
http://www.fishpalace.org/disease.htm