Featured Image for Seafood Poisoning - Marine Toxins and What You Need to Know - Part 2: Fin Fish

We in America love our fish and shellfish, but eating these good-for-you foods comes with some risk. In Marine Toxins and What You Need to Know – Part 1, we examined marine toxins in shellfish.  Marine toxins are chemicals and bacteria that occur naturally in marine waters. These toxins and bacteria can contaminate seafood under the right conditions and when consumed, can cause numerous and sometimes serious illnesses. In this article we will focus on the two common types seafood risk associated with marine toxins in fin fish. Both of these illnesses are quite common but are relatively easy to avoid.

Scombrotoxic fish poisoning

Scombrotoxic fish poisoning is also known as scombroid or histamine fish poisoning. This type of poisoning has been reported worldwide and is one of the most common types of illness related to fish consumption.

Scombroid poisoning is caused by deterioration and bacterial spoilage of certain fish species.  These fish have naturally high levels of histidine in muscle protein.  If the fish are not cooled and kept cool immediately after catch, they begin spoiling.  Bacteria in the fish produce an enzyme that converts the histidine into histamine.  Very high levels can be reached relatively quickly.

Important: The histamine toxin cannot be destroyed by cooking, smoking, canning, freezing or curing. In other words, you can’t do anything to the fish to make it edible.

You are most likely already familiar with the fish that are at risk.  Tuna and mackerel are most often contaminated and less often, mahi-mahi, sardines, anchovy, herring, bluefish, amberjack, bonito, lionfish and marlin.

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Consuming spoiled fish with excessive levels of histamines can result in illness in as little as 2 minutes to 2 hours after consumption. Individuals may experience symptoms such as facial flushing, rash, itching, diarrhea, vomiting, flushing, sweating, headache, blurred vision, and palpitations. Some victims experience a burning sensation in the mouth, a metallic taste and perhaps some abdominal pain. In rare cases individuals may also experience respiratory compromise, arrhythmias and hypertension/hypotension.

If you get sick

The good news is that most individuals experience relatively minor symptoms which clear up in a few hours.  Doctors point out that a severe reaction may be ameliorated by antihistamines or epinephrine.  Individuals taking isoniazid or doxycycline may suffer more severe symptoms because these drugs can slow processing of the histamine by the liver.

 Protecting yourself

 Here are some things you can do to avoid scombroid poisoning from spoiled fish.

  • If you think for any reason that the fish may be even a little bit spoiled, don’t eat it. Remember that the toxin cannot be destroyed by any type of cooking.
  • If the fish looks fine, but you notice that it has a peppery, salty, sharp or bubbly taste, do not eat it.  There is likely a very high level of histamine contamination.
  • If the fish was caught recreationally, be sure that it was stored on ice immediately after catch and that it is not allowed to lie around on the dock.  Toxic levels of histamines can occur in the fish in as little 6 to 8 hours.
  • Always store unfrozen fish at home at 38°F or less.  Consume within three days.
  • Extra precaution: Do not assume that just because you bought a frozen fish that it will be safe.  If the fish was too long at ambient temperature before freezing or if it partially thawed in transit, spoilage may have begun.

Ciguatera poisoning

Ciguatera is caused by eating contaminated tropical reef fish and is the most commonly reported seafood poisoning in the world, with more than 50,000 cases reported annually.  It is estimated that the number of cases is severely under-reported, perhaps by as much as 90 percent. As you can see, ciguatera is a very common type of seafood poisoning.

The ciguatera poison (ciguatoxin) is produced by a certain type of microalgae (Gambierdiscus toxicus).  The algae are consumed by small fish, which are eaten by larger fish, and so on up the food chain.  This allows the ciguatoxin to become concentrated in predator reef fish near the top of the food chain.

Reef fish that are likely to be contaminated with ciguatoxin live in warm, tropical waters between about 35°N and 35°S latitude.  This includes common destinations such as Hawaii, Guam, various islands in the South Pacific and Indian Ocean, the Philippines and Australia, and islands in the Caribbean such as Puerto Rico and the Virgin Islands.  You can see an excellent map of reported instances in the past ten years here at Harmful Algae. Sport fisherman are most likely to encounter these fish, but small fishing companies that sell their catch locally are also sources of these fish.  This is something you might keep in mind if you travel to any of these areas on business or pleasure.

The types of reef fish that have been identified with ciguatoxins are numerous, but some of the most common ones are barracuda, several different groupers, various types of snapper, amberjack and king mackerel, as well as mullet, sea bass, and eel. For those of you preparing these fish for consumption, the ciguatoxin tends to accumulate in the intestinal tract, head and roe of the fish.

Important: Ciguatoxins do not change the texture, taste or smell of the fish. The toxins cannot be destroyed by gastric acid, cooking, smoking, freezing, canning, salting or pickling.

Ciguatoxin is very potent; it only takes a little to make you sick. Symptoms of ciguatera poisoning can begin as early as 30 minutes to 30 hours after consuming contaminated fish. Individuals usually first experience gastrointestinal symptoms such as nausea, vomiting, diarrhea and cramps. Victims may also experience some cardiac symptoms such as bradycardia (slow heartbeat) and low blood pressure (hypotension).

If the illness is severe, neurologic symptoms may begin to appear, including headache, muscle aches, joint pain, numbness and tingling in the extremities, itching and fatigue.  A very distinctive symptom of ciguatera poisoning is a reversal of hot/cold temperature perception, where hot feels cold and cold feels hot. Fatality is rare.

Scientists have noted that for some reason, the neurologic symptoms described above are more common in fish from the Caribbean.

If you get sick

Most ciguatera poisoning cases are relatively minor and resolve within a day or two.  More severe cases may require hospitalization.  Treatment usually includes medicine to stop vomiting, IV fluid replacement and IV administration of Mannitol to address any neurological symptoms.  When in doubt, get treatment.  Ciguatera poisoning can have long-term consequences lasting weeks or months.

Protecting yourself 

Here are some things you can do to avoid scombroid poisoning from spoiled fish.

  • If you think for any reason that the fish may be even a little bit spoiled, don’t eat it. Remember that the toxin cannot be destroyed by any type of cooking.
  • If the fish looks fine, but you notice that it has a peppery, salty, sharp or bubbly taste, do not eat it.  There is likely a very high level of histamine contamination.
  • If the fish was caught recreationally, be sure that it was stored on ice immediately after catch and that it is not allowed to lie around on the dock.  Toxic levels of histamines can occur in the fish in as little 6 to 8 hours.
  • Always store unfrozen fish at home at 38°F or less.  Consume within three days.
  • Extra precaution: Do not assume that just because you bought a frozen fish that it will be safe.  If the fish was too long at ambient temperature before freezing or if it partially thawed in transit, spoilage may have begun.

To learn more about marine toxins in shellfish, see our Food Sentry article Marine Toxins and What You Need to Know – Part 1: Shellfish. After you’ve read both of these articles, you can be confident in the use of your knowledge to make better, safer seafood choices.