Japan’s most dangerous delicacy is getting harder to prepare safely as warming seas push different pufferfish species into the same waters, where they are inbreeding to produce hybrids whose lethal toxins are not yet fully understood.Fugu – the collective Japanese name for several species of edible pufferfish – is prized as much for the danger surrounding its preparation as for its subtle flavour.Many species contain tetrodotoxin, a powerful neurotoxin with no known antidote that can cause...