Fish - healthy or toxic?

Fish - healthy or toxic?

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Fish on the table - healthy, endangered or toxic?
Fish contains important nutrients, vitamins and fats, and many who want to eat healthily are increasingly replacing red meat with fish dishes. However, consuming it indiscriminately is neither sustainable nor healthy.

First of all, species at the top of the food chain contain high concentrations of mercury and other toxins, such as sharks or swordfish, secondly, 85% of the world's stocks are overfished and many valued edible fish are threatened with extinction.

Protein and vitamin bomb

Fish contains up to 20% protein, which is good for the metabolism, because the body immediately converts 30% of the protein calories. Protein helps against binge eating because it keeps blood sugar levels low.

Protein is necessary so that muscles can form. Food contained in fish can also be digested very well.

Omage-3 fatty acids

Fish contains omega-3 fatty acids, polyunsaturated fats that strengthen the cardiovascular system, prevent infections and support brain functions. The body cannot produce these fatty acids itself, so we have to take them. The best source for this is the “meat of the sea”.

A lot of these fatty acids contain so-called fatty fish, among the common food fish are salmon, mackerel and herring. The fish can be fresh, smoked or pickled, the unsaturated fatty acids are preserved.

Vitamin D

Our body develops vitamin D from sunlight. Young people are dependent on vitamin D - if they are not there, the bones will not grow.

People with crooked bones often suffer from a vitamin D deficiency. Brittle teeth and tooth loss also indicate vitamin D deficiency.

Schizophrenia and depression are probably associated with the fact that the brain receives too little vitamin D, inadequate kidneys prevent the body from producing vitamin D itself.

High levels of vitamin D are important for people suffering from multiple sclerosis and to prevent cancer. Vitamin D also helps against cancer that has broken out. Studies have shown that it inhibits tumor growth, at least in colorectal cancer, prostate cancer, breast cancer, lung cancer and skin cancer.

Vitamin D regulates the calcium and phosphate balance in the body. It organizes the calcium build-up in the bones and helps to extract calcium from the food, it also levels the calcium level in the blood. When it sinks, a preform of vitamin D calcitriol is formed, which releases calcium from the bones and thus increases the level in the blood.

A balanced calcium level is necessary so that the nerve cells transmit stimuli and the muscles work.

Fish is vital for people in northern countries with long dark winters such as Norway, Northern Russia or Finland - without it they would not have had vitamin D in winter. Salmon and cod are staple foods here.

Other foods also contain vitamin D, but none come close to fatty fish. Russian dishes with combinations of cod and porcini mushrooms that are unusual for Central Europeans offer vitamin D in quantities, as do avocados filled with tuna.

Offal such as liver, eggs and milk products, porcini and shiitake mushrooms also contain vitamin D and avocados.

In industrialized countries, lifestyle leads to a lack of sunlight and thus vitamin D. We spend most of our time in closed rooms, on the train or in the car and not outdoors.

Regular walks and fish on the table can make up for this lack. Around 200 g of high-fat fish per week are almost enough to meet the vitamin D requirements of a healthy adult.

However, old people should eat a lot more salmon or matjes. Over 65 the in-house production of vitamin D from sunlight works less and less, and fish can help here two or three times a week.

The absolute star among the vitamin D suppliers is the smoked eel. It contains around 90 micrograms of it per 100 milligrams, fresh eel “only” reaches 20. Unfortunately, the European eel is threatened with extinction, and WWF like Greenpeace say: stay away.

Smoked sprat, humpback and matje herring with between 28 and 33 micrograms per 100 grams are still rich in vitamin D, as are trout with 22 and salmon with 17 micrograms. Low-fat species such as the redfish with 2.30 micrograms are far behind. Since redfish are also threatened, we shouldn't eat them anyway.

Iodine and fish consumption

The thyroid gland cannot work without iodine, and this thyroid gland in turn produces hormones without which the metabolism cannot work. Pregnant women and mothers with infants need iodine in large quantities.

Salt has been mixed with iodine for a long time to prevent widespread iodine deficiency. We can do that better with sea fish.

The top seller is haddock with 417 micrograms of iodine per 100 g of fish, the all-round supermarket fish saithe, contained in fish burgers - or chopsticks, still has 263 micrograms, plaice at 291 and cod at 120, tuna "only" at 50.

But it is also advisable not to eat most types of tuna: their stocks shrank by over 90% in two decades. Bluefin tuna, for example, could share the fate of Dronte and Beutelwolf in a few years.

Selenium also supports the thyroid and is abundant in fish.

Poisons in fish

Despite omega-3 fatty acids, vitamin D, iodine and selenium, fish consumption is not without problems. Seas, rivers and lakes are polluted with pollutants.

Animals ingest these substances through food. The basic rule is: the higher up an animal is in the food pyramid, the higher the concentrations of toxins in its body. The most common poisons found in fish are polychlorinated biphenyls (PCBs) and mercury.


The amount of mercury is highest in the large predatory fish, which are also popular edible fish: sharks, swordfish and marlin, tuna and bonitos.

A study in Austria from 2007 to 2015 showed that trout, carp, char, sardine, sprat, herring, salmon and Alaska pollack were only slightly contaminated.

Mean values, which were also below the legal limit values, showed pikeperch, cod, cod, mackerel, anchovy, plaice, sea bream, sea bream, halibut and sea bass.

Mercury concentrations that were too high showed tuna, snappers and especially butterfish. The butterfish was 677 micrograms per kilo - with a tolerated value of 1000 micrograms for high-fat fish. .

Seven of 1,751 samples exceeded the limit values.

Mercury poisoning

Mercury poisoning arises when mercury accumulates in the organism. This is exactly what happens to fish that are at the top of the food chain and to people who eat these fish abundantly.

Such excess mercury can cause fetal deformities, reduce nerve growth and disrupt brain functions. The consequences are disturbances in learning and "stupidity".

Too much mercury reduces oxygen in the red blood cells, disturbs the heart rhythm and increases blood pressure. The risk of suffering a heart attack increases, as well as disorders of the immune system, which in turn promote allergies, asthma and chronic fatigue syndrome.

In addition, the risk of autoimmune diseases increases, and those affected are more susceptible to viruses, bacteria and fungi.

Breathing difficulties also favor mercury poisoning. Bowel problems and loss of energy are among the main symptoms. Too much mercury also damages the stomach and intestinal mucosa. In particular, mercury changes the bacteria in the intestinal fauna.

According to the three criteria of frequency, contact with people and toxicity, mercury is the third most harmful substance - after arsenic and lead.

How the poisoning manifests itself, however, depends on how much mercury we ingest, what state it is in, whether we ingest it or inhale it. If it accumulates in the body, outbreaks of poisoning can alternate with symptom-free times.

Mercury breaks through the blood-brain barrier, causing toxins to accumulate in the brain. Free oxygen radicals are formed, nerve cells die, the dopamine balance breaks down, and the brain no longer produces messenger substances to the required extent.

Mercury also damages the entire hormonal system, poisons the kidneys and damages the areas of the brain that organize the movements.

Mercury damages the pituitary, thyroid and thymus glands, it accumulates in the ovaries, testicles and prostate, leading to impotence and infertility. It lowers the number of sperm and triggers menstrual pain.

It damages the embryo in the womb and is quickly transferred to the fetus via the placenta.

Mercury directly damages the DNA, it blocks the RNA and thus prevents the genetic information from being transferred to proteins.

The damage mercury does in the blood affects the fetus. The blood no longer adequately supplies it with oxygen, amino acids, glucose, magnesium, zinc and vitamin 12.

How does the mercury get into the sea?

In the industrial age, the mercury content in the sea surface rose by 300%, and this is also evident in the fish that live in this contaminated water.

Scientists from the University of Michigan compared the mercury levels of yellowfin tuna from the Hawaiian waters in 1971, 1998 and 2008. It is found in cans, sushi and as steaks in the freezer.

Accordingly, the mercury values ​​of the tuna have continuously increased since 1998, by around 3.8 percent per year. The study showed that fish from the open sea also have a higher concentration of mercury.

Among other things, mercury is released into the atmosphere through burnt coal. Near-natural waters also absorb the substance through the air.

The Canadian Medical Association published a report in 1976 that Canadian Inuit suffered from mercury poisoning, people who ate more than a pound of fish a day.

Fish contaminated with mercury

Most studies agree which fish species have the highest mercury levels - but only as a rough guideline because there are large differences within the species from population to population.

The highest amounts of mercury include: grouper, spearfish, Atlantic sawing belly, torpedo bass, king mackerel, large sharks, large tuna, swordfish and marlin.

High values ​​show: eagle fish, halibut, sea trout, blue bass and blue fin tuna.

Carp, mahi mahi, herring, anglerfish, perch, most rays, cod and Pacific tuna have low values.

The lowest values ​​show anchovy, redfish, saithe, catfish, flounder, sole, haddock, salmon, sturgeon (including caviar), sardines and lake trout.


Fish suffer from many diseases that are also dangerous for humans. Most pathogens die from heating, so that cooked, fried or grilled fish pose a low risk. The situation is different with sushi, which is now also getting into the stomach more and more outside of Japan.

1) Solomonella

Fish near the coast that are additionally weakened by sewage often show high concentrations of bacteria that trigger salmonellosis.

2) parasites

Various parasites, especially round worms, thrive in fish. In the human body, they lead to abdominal cramps and vomiting. These nematodes spread via living larvae in the fish body, which also nest in the human intestine.

If the fish is heated, the worms die.

Endangered enjoyment

The global stocks of many edible fish collapse. On the one hand, this is due to the fact that the pH value in sea water shifts due to CO2 emissions - the oceans become acidic.

Plastic waste pollutes the oceans. Turtles die because they think and eat plastic bags for jellyfish; even on remote islands, the beaches are covered with plastic.

Edible fish eat small parts of the plastic with plankton, and we absorb this plastic when we eat the fish.

Overfishing brings various species to the brink of extinction. Factory ships with huge trawls destroy the entire seabed, they carry everything with them and leave an ecological fiasco - as if you were pulling out a forest with its roots and then looking for the deer.

Around 23 to 73 million sharks are killed annually, according to the Sharklife organization - and that for shark fin soup alone, which the Chinese appreciate. The fishermen usually cut the fins of the animals alive and then throw them back into the sea.

There are also around 100 million sharks that end up as bycatch in the fishing nets, with them sea turtles, dolphins, whales and seals.

85% of the fish stocks are overfished today, 40% of the catch is by-catch, and this increases to 90% in trawls.

Aquacultures usually do not lessen the problem, but exacerbate it, because the farmed fish are fed with fish meal and fish oil.

Aquaculture operators often destroy sea lions, dolphins and other fish eaters.

Sustainable consumption

If you want to eat fish without promoting the destruction of marine fauna, you should pay attention to sustainability.

Sustainable consumption pays attention to the following:

1) How endangered is the fish species and the corresponding population?

2) How gentle are the fishing methods? Trawls are NO-GO. Special fishing rods that only target the target species are more suitable.

3) Ecologically sound aquaculture can be an alternative. Are aquacultures damaging ecosystems, for example mangrove forests?

Organic seal on fish

Certified organic seals help you make your decision in the supermarket. The Marine Stewardship Council (MSC), Bioland and Naturland for aquaculture and also followfish pay attention to sustainability.

Greenpeace and the WWF offer free shopping guides, but the results are somewhat different. Greenpeace's criteria are stricter than WWF's.

Greenpeace created eleven negative criteria. If one of them applies, it means: fingers away. This includes not only the size of the stock, but also fishing in sensitive ecosystems, destructive fishing methods such as trawls and high by-catch. Greenpeace therefore only recommends trout, herring, carp, mackerel and pikeperch.

Little threatened are: herring from the Northeast Atlantic, cod from the eastern Baltic Sea, salmon from the American Pacific, mackerel from the North Atlantic, anchovy from the Biscay, saithe from the Northeast Arctic, tilapia from cultures in Honduras, Indonesia, USA and Europe, Bonito from the Maldives.

Still okay, but second choices are Alaska pollack from the NW Pacific, trout from Northern Europe, halibut from Norway and the Northeast Arctic, herring from the Baltic Sea, cod from Iceland, Norway and the Baltic Sea, salmon from Iceland, Norway and Scotland, anchovies from Spain and the West Atlantic, sardines from the Mediterranean and Northeast Atlantic, haddocks from the Arctic, Norway and the North Sea, bonito from the West Pacific and pikeperch from Europe.

You should avoid European eel, spiny dogfish (especially Schillerlocken), trout and salmon from Chile, pomegranate, all other sharks and rays, halibut from the NE Atlantic, cod from the NO Atlantic, mackerel from the eastern Middle Atlantic, blue marlin , Swordfish, redfish, plaice from the north-east Atlantic, anglerfish from the NE Atlantic, plaice from the Mediterranean, red snapper, red tuna, bluefin tuna, Victoria bass and pikeperch from Eastern Europe.

Aquaculture - an alternative?

Aquacultures were celebrated as the "blue revolution". Not only can fish be produced in large quantities, but conservationists also viewed aqua farms positively in order to limit overexploitation in the oceans.

Most of these aquacultures, however, are just as much an ecological disaster as palm oil plantations in destroyed rainforests. The mangrove belt of South Asia was relatively spared from the devastation of other ecosystems such as savannah or dry forest before the "blue revolution" because the brackish water zone could not be used industrially.

With aquaculture for shrimp farming, this changed rapidly - more and more mangrove forests were turned into shrimp farms.

Aquaculture already comprises a third of the fish consumed. Especially carp, catfish, trout and tilapia perch are bred here, and increasingly tuna, sea bream and sea bass. Cod, sole and sturgeon will also come from farms in the future.

Except for carp and catfish, they are predatory fish. They need fish as feed, so a kilo of farmed salmon devours five kilos of feed fish.

In aquacultures that do not pay attention to sustainability, faeces and medication from farmed fish pollute the surrounding water in lakes, rivers and oceans.

If the fish meal for the fish feed comes from wild catches, then an aquaculture fish consumes several times its weight in wild fish.

For example, the farms for Pangasius catfish in Vietnam are horrible: Up to 80 fish in one cubic meter of water ensure that the animals cannot move. Since they are constantly injured, they are stuffed with up to 50 antibiotics, pesticides prevent algae growth.

Salmon farms in Chile are also contaminated with medication: The 2007 annual report from Marine Harvest showed that 0.02 g of antibiotics were used for every ton of salmon in Norwegian farms, in Chile it was 732 g, which is 36,000 times as much. In 2008 salmon farms in Chile consumed 325 tons of medication, Norway only one ton. 40% of antibiotics are also banned in the United States.

Aquacultures for herbivores that feed on organic waste are ecologically harmless. In Europe these are carp, in Asia grass carp and various catfish. They even live in rice fields and provide a kind of permaculture. Your droppings are used as fertilizer for aquatic plants, which in turn eat the fish.

Ecological companies only use fish meal as remains of the fish industry. 60 fish farms in the Naturland chain only allow fish weighing ten kilos per cubic meter of water.

Naturland produces carp, trout, salmon and catfish, all of which bear the Naturland seal, but are also more expensive than from conventional farms.

"Support your local dealer"

If you like fish on the menu, you should ask yourself whether it is absolutely necessary to have exotic animals that are caught in questionable conditions. Carp, trout or zander from local fish ponds are harmless.

Traditional fish farming areas such as the Lausitz pond landscapes or the Meißendorfer ponds near Winsen / Aller are now hotspots of endangered animal species such as otters, sea eagles and red-bellied toads.

Fish are part of the ecosystem and fish farming ensures that this ecosystem remains intact. (Dr. Utz Anhalt)

Author and source information

This text corresponds to the requirements of the medical literature, medical guidelines and current studies and has been checked by medical doctors.


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  • Scinexx - the knowledge magazine: (accessed: June 17, 2016), more and more mercury in tuna
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Video: Farmed Norwegian Salmon Worlds Most Toxic Food (December 2022).