In the United States, it is extremely rare for individuals to become ill from eating finfish. Even raw finfish, if prepared in a clean environment, is almost never a source of human illness. Only 5 percent of food borne illness is seafood related and 85 percent of those cases involve shellfish.
Worldwide, the most common and serious illness related to consuming finfish is ciguatera, a disease that is rare in U.S. waters. A less serious illness is scombroid, or histamine, poisoning caused by improper handling. Bacterial cross-contamination from other foods and improper hygiene is perhaps the most common cause in illness from raw, prepared and smoked fish. The illness that effects us the least, yet scares us the most is that of parasitic worms.
Ciguatera is an illness brought about as a result of fish eating marine algae that are the sources of natural toxins, and is most commonly found in reef-dwelling tropical species, particularly those that prey on other fish. Barracuda, moral eels and various jacks should be avoided in all parts of the Caribbean. Large groupers, snappers and other species may also bio-accumulate dangerous levels of the ciguatera toxins, concentrating in the viscera, livers and gonads of fish. Cooking or freezing does not inactivate the toxins, and there is no antidote. Avoidance is the only solution.
Cases of ciguatera have been reported in Hawaii, the southern tip of Florida and the Caribbean, but U.S. waters in the Northern Gulf of Mexico and Southeast Atlantic are not associated with this illness.
Symptoms generally include nausea, vomiting and diarrhea, tingling or numbness, itching and hot and cold sensation reversal, and in worse cases, difficulty breathing or respiratory failure from muscle paralysis. There is no treatment, but symptoms usually subside within days.
Members of the Gempoylidae, or snake mackerel family, contain indigestible waxy esters in their fatty tissues similar to those found in Olestra, and these esters have powerful laxative properties that affect people to varying degrees.
Escolar and oilfish caught in the South Pacific and Gulf of Mexico are two such fish, and are quite delicious, popular menu items. Freezing and cooking won't inactivate gempylotoxins, so eating no more than 3-5 ounce servings or avoiding it is the only solution.
Symptoms of this illness are illusive, sudden, and without warning. You can be affected at any time or in the most inappropriate place, and the results can be quite embarrassing, not to mention unhygienic.
This common infection of marine fish by parasitic protozoa poses no threat to human health, but does effect the appearance and texture of many fish such as tuna, hake, sand dabs, halibut and farmed salmon. After the host fish dies, the protozoa produce enzymes that attack the flesh and create soft spots in the fish.
The parasites can be destroyed by thorough cooking and freezing. Kudoa is the major reason why much of the tuna destined for the sashimi trade is frozen.
Listeria is a bacteria found everywhere in nature and its control depends on proper handling and clean processing facilities. Although found more commonly in foods other than seafood, listeria's ability to resist cold temperatures makes it a concern. Cold-smoked fish, or uncooked fish that is stored for long periods of time under refrigeration, is the most likely seafood-related vector.
Lysteriosis usually causes mild flu-like symptoms in healthy adults, but it can be serious for infants and anyone with immunosuppression. Pregnant women should be particularly careful because it can result in miscarriage.
When purchasing smoked fish in a vacuum-sealed package, be sure that the packaging is intact and the seal has not been breached.
Scombroid, or histamine poisoning, is a mild disease of short duration. The toxins associated with scombroid poisoning are formed during cleaning, when bacteria that is normally found on the skin of the fish, spreads to the flesh of the fish, where the proteins can produce histamine-like allergens. While scombroid fish, members of the tuna family that are warm-blooded and don't chill down quickly, are susceptible, mahimahi, bluefish, escolar, and other fish have been implicated as well.
Scombrotoxin is not easy to detect, so you'll have to rely on the good fish-handling practices of your fish dealer. Seafood contaminated with histamine does not look or smell spoiled, and the effects of the histamines are not diminished by freezing or cooking.
The most common symptoms are facial flushing, itching, and rash although nausea, vomiting and headache my occur. Often, the first sign is a distinctly sharp, peppery, or metallic taste, along with a tingling or burning sensation in the mouth. In most cases, an over-the-counter antihistamine like Benadryl is enough to produce relief.
Only a few of the more than 100 species of fish that can inflict a venomous sting can be found in a fish market, but during handling, it can happen and result in moderate pain and swelling. Venom can be injected through dorsal, anal or pelvic spines.
All Pacific Coast rockfish are venomous, some more than others. Catfish, scorpion fish, skate and some shark have venomous spines. Those repeatedly stung can develop serious allergic reactions to the venom.
Being stuck by the spine of any fish can lead to serious bacterial infection including septicemia, so all wounds should be washed immediately, then soaked in a 1-to-1 salt to hot water bath for 5 minutes, repeating the soaking twice. If pieces of the spine remain in the wound or infection occurs, see your doctor immediately.
All animals and plants host numerous parasites, and there are a few that may effect our health.
Four parasites in seafood are cause for concern; two types of roundworms, and two broadfish tapeworms. These worms all go through a complex life cycle involving living inside a crustacean, then a fish, and then a mammal - in order to reproduce. These parasites and the fish they infect, including cod, flounder, haddock, fluke, Pacific salmon, rockfish, herring, monkfish and others, are most abundant where there are fish-eating mammals like sea lions, Alaskan grizzly bears and raccoons.
Cod and herring worms are approximately three-quarters to one inch long and are the thickness of a pencil lead. One species is brown, and easy to see. The other is white, and can coil into a tight circle that looks like a bull's eye and is harder to notice. Both can be found in a variety of fish and the occasional squid.
If a worm is ingested, in most cases it will pass right through the digestive system, but on extremely rare occasions the worm may try to attach itself to the lining of the stomach or intestine, causing stomach pain and nausea that could be misdiagnosed as an ulcer or appendicitis.
Both cod and herring worms are incapable of surviving in humans and are eventually digested. Like other parasitic worms, cod worms are destroyed by thorough cooking or freezing.
Two varieties of tapeworms commonly infect fish and can be contracted by humans, D. latum is found in freshwater and anadromous species, like salmon, that spend part of their lives in fresh water. Alaskan bears are hosts in the Alaskan watersheds. D. pacificum uses marine mammals like sea lions and seals as hosts, so it can be found anywhere they're present.
The larval stage of the tapeworm measures from 4 to 5 millimeters in length and appears as a large cream-colored rice-grain shaped cyst embedded in the flesh of the fish.
Hosting a tapeworm is often asymptomatic, although stomach distress or anemia may sometimes occur. Infection is usually diagnosed by the presence of tapeworm eggs in the stool, and antihelminthic, or deworming, drugs are then administered as treatment.
Tapeworms are destroyed through cooking or freezing.