Know this before you eat tuna next time
Yellow fin tuna products sold in the U.S. are being recalled, through an order by the Food and Drug Administration, because they can cause a type of food poisoning called scombroid fish poisoning. This happens when people eat fish that's contaminated with high levels of histamine, a compound that causes allergy like symptoms.
The contamination occurs when the fish are not properly refrigerated and bacteria break down the fish's flesh, resulting in high levels of histamine. Symptoms of scombroid fish poisoning can include a tingling or burning sensation in the mouth, facial swelling, rash, hives and itchy skin, nausea, vomiting and diarrhoea, flushing of the face, headache, faintness, sometimes with blurring vision, abdominal cramps, wheezing or other breathing problems, a tight feeling in the throat, or a metallic or peppery taste in the mouth.
Symptoms of Scombroid poisoning typically begin within 5 to 30 minutes after eating the fish, and last a few hours. In some cases, symptoms can persist for a few days. Sometimes antihistamines can help. In severe cases, a trip to a hospital emergency room is necessary for care with IV fluids, oxygen or other medications and treatments. Histamine poisoning can be life-threatening in persons with conditions such as asthma and heart disease. Symptoms related to histamine poisoning can also be similar to those of coronary heart disease, increasing the possibility of an invasive medical intervention if misdiagnosed. There is insufficient knowledge about it in the medical community in India.
Some kinds of fish contain naturally high levels of the chemical histidine. This chemical is converted to histamine by bacteria. Unrefrigerated, or improperly transported, fish of the families Scombridae and Scomberesocidae (e.g. tuna, mackerel, bonito), are commonly implicated in incidents of histamine poisoning, which leads to the term, "scombroid fish poisoning", to describe this illness. However, certain non-scombroid fish, mahi-mahi, bluefish, and sardines, anchovy, herring when spoiled, are also implicated in histamine poisoning.
Histamine is a naturally occurring compound that helps regulate specific functions of your digestive, nervous, and immune systems. If you’ve ever experienced an allergic reaction, you’re probably familiar with common symptoms associated with elevated histamine levels, such as nasal congestion, itchy skin, headaches, and sneezing. You may also ingest histamine through your diet – it occurs in certain foods like cheese, wine, pickles, and smoked meats.
The Tuna samples, that have caused this recall, had histamine levels above the Food and Drug Administration regulatory level of 50 ppm (levels were between 213 and 3245 ppm). In most cases, the tuna used to prepare burgers and salads was frozen and thawed more than once before serving. Tuna ground for burgers and sandwiches can be susceptible to both, temperature fluctuations and bacterial contamination.
Tuna is served raw as sushi, sandwich fillings and salad, and cooked as filets, steaks, burgers. Tuna is canned in oil, brine, water, and sauces, and used for sandwiches and salads. Some parts of the meat are used as canned pet food. Canning retains any histamines that may have been produced by bacteria.
Tuna is brought to cities from both local and international waters. It is supposed to be refrigerated from the minute it is caught. But most Indian fishermen bring it in the hot sun to port only a few hours later. From there it is supposed to go in refrigerated trucks and this takes 7-14 days.
The fish meat is put into freezer bags and stored in freezers for 2 to 4 days until served as salads, steaks, filets or burgers. It is taken out at intervals to be ground into patties, and restored in the cooler until cooked and served. This requires several freezing and thawing cycles. These food-handling practices are common to all restaurants that serve tuna. Inadequate refrigeration, dirty grinders, are some of the problems discovered in restaurants. Histamine poisoning from fish is probably the principal cause of morbidity from toxic fish consumption worldwide.
Histamine development is more likely to occur in raw, unfrozen fish. Because the fish might appear and smell normal, the consumer is unlikely to identify a problem before eating the fish. Once the bacteria have formed the enzyme histidine decarboxylase, histamine production can continue even if the bacteria are killed. The toxins produced are heat stable and, once formed, are not destroyed by cooking, smoking, or freezing.
Tuna are especially vulnerable to temperature fluctuations, because their average body temperature when caught tends to be several degrees warmer than that of other types of fish. Thin pieces of fish, such as the belly meat used for ground tuna and salads, are more vulnerable to temperature fluctuations.
Violation of storage and temperature controls are also more likely with tuna used for salads and burgers, because pieces are stored over a longer period than filets and exposed to multiple thawing and refreezing cycles. The grinding process, used to make tuna burgers, can contaminate the fish by either mixing histamine-forming bacteria into previously uncontaminated material or by increasing the temperature of the tuna through mechanical friction.
Currently, tuna are caught in gill nets, which causes the fish to get bruised and injured when they try to fight their way out. By the time the nets are hauled, and catch sorted, many hours pass after death and histamines build up.
Histamine levels should remain below 100 ppm, which is possible when tuna is frozen immediately after catching, but in tropical countries with poor freezing facilities, levels are known to rise above the acceptable threshold, even if the fish remains above 4 degrees Celsius for five minutes. In India, tuna are sold in the open, with no ice (along with seerfish and mackerel).
Tuna is now being pushed by this government. Till now, most of it was sold in Kerala and Goa and is not among the most preferred species in the domestic market, because it is not traditionally caught. It is being promoted for domestic customers through the Ocean Partnerships for Sustainable Fisheries and Biodiversity Conservation, a World Bank/GEF-funded project, and the Bay of Bengal Programme Inter-Governmental Organisation (BOBP-IGO), headquartered in Chennai.
The Indian seas, according to the Central Marine Fisheries Research Institute, have nine species of the fish. But the tuna that are brought in are not maintained well. Indian vessels are relatively small, do not use on-board refrigeration, and depend on ice, which limits the amount of fish that can be properly stored. This is being sought to be changed, so that more tuna can be caught. The object is to compete with the US and France.
But, is this the time to promote a fish that is considered dangerous to health?
Tuna is known for its mercury content. Many fish species carry high levels of the metal mercury — a dangerous contaminant that can affect the nervous system. Pollution has raised mercury levels in our oceans. This mercury is consumed by fish and converted to a toxin known as methylmercury. Fish, like tuna, are high on the food chain. They consume other contaminated fish, compounding their mercury levels.
Children are vulnerable, as their developing nervous systems are particularly vulnerable to mercury’s effects. In March 2004, the United States FDA issued guidelines recommending that pregnant women, nursing mothers, and children, limit their intake of tuna and other predatory fish. A January 2008 report revealed potentially dangerous levels of mercury in certain varieties of sushi tuna, reporting levels "so high that the Food and Drug Administration could take legal action to remove the fish from the market."
While fish like bass, carp (rohu), cod (gobru), lobster, snapper, have moderate amounts of mercury and are advised to be eaten less than six times a month, and not by pregnant women and children, tuna ranges from medium (Canned Chunk light) to high (less than 3 servings a month) Tuna (Canned Albacore, Yellowfin) to highest mercury (avoid eating): Shark, Swordfish, Tuna (Ahi). Among those calling for more warnings, about mercury in tuna, is the American Medical Association.
Environmentally tuna is about the worst fish to eat.
Dolphins swim beside several tuna species. Tuna schools associate themselves with dolphins for protection against sharks, which are tuna predators. Commercial fishing vessels exploit this association by searching for dolphin pods. Vessels encircle the pod with nets to catch the tuna. But the nets entangle dolphins, injuring or killing them. 1 million tonnes of tuna are caught annually, but the 'bycatch', which is fish that is discarded because it is not tuna, runs into millions of sharks, turtles and other oceanic fish.
According to the International Seafood Sustainability Foundation, Indian Ocean yellow fin tuna, Pacific Ocean bigeye tuna, and North Atlantic albacore tuna, are all overfished. A 2010 tuna fishery assessment report, released in January 2012 by the Secretariat of the Pacific Community, supported this finding, recommended that all tuna fishing should be reduced.
In 2010, Greenpeace International added the albacore, bigeye, bluefin and yellowfin tuna, to its seafood red list, which are fish in danger of becoming extinct. The bluefin, are now considered by IUCN as critically endangered.
Research shows that increasing ocean temperatures are taking a toll on tuna in the Indian Ocean, where rapid warming of the ocean has resulted in a reduction of marine phytoplankton.
Is tuna what India needs on its plate?
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