Sorry for your loss. I remember how sad I was when "Spot", my African bullfrog died. He was my companion for 12 years. I do know that the large species of frogs, like "pacmans", bullfrogs and White's treefrogs are very prone to obesity. If untreated can lead to kidney failure and eventually death. Sometimes, you can get a diseased or stressed out animal even at the best pet shops - it may not be your fault at all.