This type of fish can be contaminated by scombrotoxin, which causes flushing, headaches, and cramps. If it is stored above 60 degrees after being caught, fresh fish can release the toxin, which cannot be destroyed by cooking (and is unrelated to mercury contamination or other problems related to tuna and other fish). Tuna has been linked to 268 scombroid poisoning outbreaks since 1990.
Before being transformed into a pricey delicacy, oysters lurk on the ocean floor doing what they do best – filter feeding. And if the water they are filtering is contaminated, so are the oysters. (Or they can be contaminated during handling.) If served raw or undercooked, oysters can contain germs – mostly a gut-churner called norovirus and a bacterium known as Vibrio vulnificus – that can cause nausea, vomiting, and diarrhea.