Two of the most well-known and most deadly fish poisons are tetrodotoxin and ciguatoxin, both of which affect the nerves.  Tetrodotoxin is associated with pufferfish/blowfish – ‘fugu’, and ciguatera poisoning is associated with reef dwelling fish such as barracuda, grouper and snapper.

For more information, see Public health response to puffer fish (Tetrodotoxin) poisoning from mislabeled product from the National Library of Medicine.