A neurotoxin with potential analgesic activity. Tetrodotoxin binds to the pores of fast voltage-gated fast sodium channels in nerve cell membranes, inhibiting nerve action potentials and blocking nerve transmission. Although found in various species of fish (such as the pufferfish), newts, frogs, flatworms, and crabs, tetrodotoxin, for which there is no known antidote, is actually produced by bacteria such as Vibrio alginolyticus, Pseudoalteromonas tetraodonis, and other vibrio and pseudomonas bacterial species.

Aminoperhydroquinazoline poison found mainly in species of puffer fishes, and some newts; the toxin causes paresthesia and paralysis through interference with neuromuscular conduction.

An aminoperhydroquinazoline poison found mainly in the liver and ovaries of fishes in the order TETRAODONTIFORMES, which are eaten. The toxin causes paresthesia and paralysis through interference with neuromuscular conduction.