What’s in fish that could make a person sick?

There are two types of food poisoning that come from eating fish. Probably the most common worldwide is scombroid poisoning. Scombroid usually results from eating ocean fish of the scombroid family, including tuna, albacore, mackerel, bonito, and skipjack. Occasionally, non-scombroid fish such as bluefish, mahi mahi and marlin have been implicated.

The poisoning is thought to develop in fish that have been allowed to remain at room temperature for a number of hours, particularly if they are not cleaned, or cleaned poorly. It appears that organisms in the fish’s intestines cause a change in the amino acids of the dark meat, producing an excess of histamine in the flesh. Other chemicals may also be involved. These toxins are not broken down by freezing, cooking, smoking or canning. Outbreaks have occurred after eating both fresh and canned fish.

What's in fish that could make a person sick?

Scromboid poisoning usually causes symptoms within a few minutes or an hour, including flushing, dizziness, burning around the mouth, nausea, vomiting, diarrhea, itching, and hives. The symptoms generally subside within a few hours. Although the poisoning has many features of an allergy, and can be relieved by antihistamines, it is not an allergy to the fish itself. Eating the same type of fish again will not cause a recurrence, unless that fish also happens to be contaminated with the toxic agent.

The other food poisoning attributable to fish is called ciguatera poisoning. Again, it results from a toxin that is not produced by the fish itself, but by tiny algae that are eaten by small fish low on the food chain, which are then eaten by larger fish, etc., until they reach a high concentration in fish at the top of the food chain such as barracuda, snapper, grouper, and amberjack. Ciguatera occurs only in fish caught in the tropics, so most cases are reported in Florida, the Caribbean, and Hawaii, though tropical fish shipped to the northern U.S. cause occasional cases. The toxin is colorless and tasteless, and does not develop because of improper handling or refrigeration of the fish: Its presence depends entirely on what the fish itself had been eating. The toxin survives freezing and cooking.

Symptoms may appear in a few minutes, but can be delayed for up to a day. Nausea, vomiting, cramps and diarrhea are most common. Itching and odd sensations around the mouth, as well as a peculiar reversal of sensation, so that hot things feel cold and vice versa, help to make the diagnosis. The symptoms may last as long as a week, but deaths are rare.

There are a number of parasites that are transmitted by eating raw or undercooked fish. They are common in Asia, where raw fish is often consumed, and have been seen more frequently in the U.S. since sushi became popular. Most parasites are found in fresh water fish, although some can be found in ocean fish, too. All the parasites can be killed by adequate cooking, or by commercial freezing.

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