What type of Puffer? Be careful with the sharpnose's (Canthigaster sp.) as they are notorious for chewing the fins of lions (remember only the top 13 spines are venomous, all other finnage is NOT). An Antennata would do pretty well in a 55, Fu Manchu would do great (these are my favorite lion and one of my all time favorite fish...just wish stores around me carried them
) and will be a little small for a Radiata but they will do ok. Hope this helps and good luck!