Unfortunately in those days i trusted the fish store geek who told me they could emit toxins, but "it rarely ever happens" I'm not sure how it died. I thought it probably poisoned itself along with everyone else. To be honest, I'm not so sure. but it was an expensive lesson. I wondered if anyone had them and had the same thing happen, and if they tox the tanks is there any antidote for their toxin??? (not that I will ever risk that again) Puffers are just as cool and no toxins. But it was cool sitting up late at night watching "Squirt" swim along the top of the tank, then suddenly raise his head and spit out a gieser of water.