Finally found an elusive Abei puffer locally a week ago, had him in a 15 gallon quarrantine tank(getting the normal new fish in my house prazi treatment). Fish was eating, everything was fine yesterday then today he was swimming into things and just up and died within about 4 hours. tank has been running for about a year (wife normally uses it for her cichlid moms to spit their fry, always some fish in it to keep it cycled) cichlids came out the day puffer went in, params were good, ammo 0, nitrite 0, nitrate <20, temp 78 and was going to move him to his permanent tank in a couple days.
Is it possible he was eating air bubbles from the bubbler in the tank and that is what did him in? I noticed he was floating funny so I squeezed his corpse a little and 4 air bubles came out. I never had the fish out of water, made the guy at the store bag him under water, made sure to release him straight from the bag to the tank underwater, even when I took the dead guy out of the tank I kept him in water (scooped him out in cool whip container).
Some days I just hate this hobby/habbit/addiction, whatever you wanna call it.

I guess it's back to searching for another Abei.