All I know is to watch it's behavior and eating habits and call a knowledgeable resource a.s.a.p. like nearest aquarium store. Fish can die fast so if you value the fish I would even call a vet. for knowledge or resources they provide. Good luck. Puffers are an amazing fish. I remember now that it could be a disease type of thing my fish had from many years ago. It's cureable with proper water addative. fix it as soon as you can though.
