If you've ever gotten sick from eating tuna, it's sort of like food poisoning but isn't really. If you've ever had an allergic reaction to tuna, it's sort of like an allergy but isn't really.
If (if?) you are hopelessly confused at this point, let's open up the can and look at what's going on.
The science of "poisoning by tuna" is rather interesting, and, although the chemical for the toxin that is responsible has an obscure name, scombrotoxin (1), you know it by its more common alias—histamine, which is formed in certain decaying fish, especially those with dark meat.
Scombrotoxin poisoning is different from "typical" food poisoning, for example, that from eating undercooked hamburger. The histamine that forms on the tuna survives cooking,...