Wednesday , 11 December 2019
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Does India need tuna on its plate?

Maneka Sanjay Gandhi

Yellow fin tuna products sold in the US 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, hives, vomiting and diarrhoea, flushing of the face, headache, faintness, sometimes with blurring vision, abdominal cramps, breathing problems, a tight feeling in the throat, or a metallic or peppery taste in the mouth. These typically begin within five to 30 minutes after eating the fish, and last a few hours. Sometimes they persist for a few days. Antihistamines can help sometimes but in severe cases, a trip to the hospital is necessary.

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. Plus, there is insufficient knowledge about it in the Indian medical community.

Some fish naturally contain 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 (for example: tuna, mackerel, bonito), are commonly implicated in incidents of histamine poisoning. 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 parts per million (levels were between 213 and 3245 parts per million).

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 seven-14 days. The fish meat is put into freezer bags and stored in freezers for two to four 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. 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 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 cause the fish to get bruised 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.

In tropical countries with poor freezing facilities, levels are known to rise above the acceptable threshold, even if the fish remains above four 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. It is being promoted for domestic customers through the Ocean Partnerships for Sustainable Fisheries and Biodiversity Conservation, a World Bank/Global Environment Facility-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 objective 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 methyl mercury. Fish, like tuna, are high on the food chain. They consume other contaminated fish, compounding their mercury levels.

Children, given 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 to high (less than three servings a month) to highest mercury (avoid eating). Among those calling for more warnings, about mercury in tuna, is the American Medical Association.

Environmentally, tuna is 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. One 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, by the Secretariat of the Pacific Community, supported this finding, and 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.

Besides this, 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 p
hytoplankton.

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