Im not fimiliar witht this type of disease, but I did do some research and nodular disease came up. The disease causes open sore and blistering like those appearent on your goldfish. The main cause of this disease is uaually the lack of water changes which cause bacteria to over develope. There are a few medications which can be bought at your LFS or LPS, that help deal with this type of disease. I usually just treat with with aquarium salt for a week or two and do regular water changes, but if the salt does not solve the problem I would stat treating with MEALFIX or other medications. Hoped I help, good luck.