2. Pufferfish
Pufferfish, also known as fugu in Japan, contain tetrodotoxin, a lethal poison with no known antidote. Just one fish carries enough toxin to kill 30 adults. Ironically, it’s considered a delicacy in some cultures—when prepared incorrectly, it can lead to death within hours. Their cute, balloon-like appearance hides one of the deadliest substances in the sea.