My purple firefish has been in my tank for about 2 weeks now and I noticed this rather large protruding cystlike spot on him yesterday. It was not noticeable when I picked him up. The tank is about 2 months old now and the only other inhabitants are a few scarlet hermits and astrae snails. He is feeding great and very active. No labored breathing, mucous buildup, or odd activity either. Any ideas?