Although it is a parasite that has been with us for a long time, in recent times its presence has increased considerably. For this reason, it is common to find citizens who demand lists of Fish without anisakisor, at least, which fish do not have anisakis or what guarantees they have against anisakis in cooked fish.
What is anisakis in fish?
Anisakis is a parasite that belongs to the nematode family. They are roundworms that infest fish that live in saltwater in mares and oceans. We will not find fish with anisakis in freshwater. In their adult phase, they live in the intestine of marine mammals such as whales, sperm whales, dolphins, seals, sea lions…
“They are considered permanent hosts, since the anisakis completes its evolutionary cycle in its digestive system, eliminating thousands of eggs into the sea every day, which develop and go through different phases,” explains Carmen Ferrer Svoboda, pharmacist, researcher and professor in the areas of Bromatology, Hygiene, Food Safety, Collective Catering, Food Technology, Microbiology and Food Toxicology at the Ramon Llull University.
Other species of fish, such as hake, cod, herring, sardines, horse mackerel, tuna, as well as various cephalopods, such as cuttlefish, squid or octopus, often become secondary or intermediate hosts. And here the problem arises: these fish are common in the human diet.
In this way, humans “become accidental hosts by ingesting fish contaminated by Phase 3 or L3 larvae or by live adult anisakis worms.”
Effects of anisakis on health
This parasite can cause allergies or a specific infection known as anisakiasis.
Anisakis allergy
The most worrying case for public health is “when we eat fish contaminated by live L3 larvae. We then suffer a allergy to anisakis«In milder cases, it can cause hives or rashes, and in more severe cases, bronchospasm or anaphylactic shock,» Ferrer Svoboda points out.
The danger lies in the fact that, from the first contact, “sensitization to anisakis antigens develops. Currently, more than 30 different ones are known, some of which could be heat-resistant and related to recently described cases of people who have suffered allergic reactions despite eating cooked fish,” warns the pharmacist.
Sometimes can be confused with a fish allergy. “The reason is that it can occur when consuming a wide variety of fish (all of them parasitized by anisakis). To avoid it, the current recommendation is that People with allergies to anisakis should only consume deep-frozen marine fish. In case of high sensitivity, and whenever advised by an allergist, avoid fish altogether.«.
For the general population, the best treatment is prevention. That is why it is necessary Avoid eating fish containing live L3 larvaeThis is achieved in two ways: destroying the larva by cooking or freezing, and not eating raw or undercooked pieces if they have not been previously frozen. This explains the famous controversy over why anchovies to be served in vinegar should be frozen, as well as fish to prepare ceviche or sushi, among others.
This rule only applies to fish. Oysters, mussels, clams, cockles and other bivalve mollusks should not be frozen..
Anisakiasis
The anisakiasis It is caused by ingesting the live adult worm. “The parasite penetrates through the digestive mucosa and produces an inflammatory reaction, which can cause abdominal pain, sometimes nausea or diarrhea. If we have been infected by the adult worm, as it cannot complete its evolutionary cycle within us, it tries to leave our body. To do this, it perforates our intestine, generating pain so acute that it can be confused with peritonitis,” warns the researcher.
In this case, the treatment is surgical by laparoscopy. The good news is that, if we have accidentally bought infected fish, the worms They are visible to the human eyewhich makes it easy to detect them. European and Spanish legislation requires that fishery products not be put on sale with visible parasites, but it cannot prevent them from sometimes arriving at the fishmonger’s with worms.
When asked ‘I found anisakis in my fish, what should I do?’, experts are blunt: If you are going to cook it, remove some of the muscle tissue closest to the viscera to eliminate most of the anisakis. Then, cook the fish ensuring that the temperature reaches at least 60ºC.eitherC in the centre, meaning it is well done. If it is to be used for lightly cooked preparations, for example marinades, also remove part of the muscle closest to the visceral cavity and freeze at -20eitherC for at least 5 days. If your home freezer does not allow this temperature to be reached, consume it cooked.
Fish with the highest presence of anisakis on the market.
In fact, all those that come from open mares such as the Cantabrian Sea, or closed ones such as the Mediterranean can have contamination by anisakis. However, the risk is greater with species captured in the Atlantic and Cantabrian, in the Mediterranean area. The custom of gutting fish at sea and throwing the entrails into the water partly explains why it is more common in large fishing grounds with large fishing fleets. It is important to bear in mind that, even if the fish was caught by us while sport fishing in any of these grounds, it can carry the parasite.
What about fish caught in freshwater? Fish caught in rivers, lakes and swamps are not infected, so there is no need to freeze them.
The same applies to freshwater farmed fish, such as trout, as long as they are not fed fishmeal.
Are there anisakis in marine farmed fish?
There is no clear answer to this question. According to the food safety specialist, “fish farms that are closer to the coast, where marine mammals are not as common, have good facilities and filter seawater, are not at risk of anisakis. However, those located offshore, in the North Sea, as is the case with salmon farming, could be at greater risk.”
To be on the safe side, whenever we use farmed salmon from deep sea fish farms in raw preparations, such as marinades, raw pickles or homemade wet salting, the best thing to do is to freeze it to destroy any possible anisakis.
Effective methods to eliminate anisakis.
There are only two ways to kill anisakis before eating fish: kill it by freezing or by cooking. In the case of preparing ceviche or sashimi, tartares (shrimp, tuna), sushi, etc. should always be frozen.
To avoid risks and unnecessary freezing, it is advisable to follow these recommendations:
- Preferably buy clean fish without guts. (sin guts). If it is not, we must remove the viscera as soon as possible.
- You should not freeze fish if you are going to cook it in the oven, boiled or grilled.. In these cases, the cooking temperature and cooking time are sufficient to destroy it.
- If frying is chosen to cook them, It is not necessary to freeze them either. In this case, the time-temperature ratio must be taken into account, as well as the size and thickness of the piece. The thicker it is, the longer it should be cooked.
- If cooking in the microwave, it is important to turn the piece so that there are no cold spots and let it rest for a couple of minutes so that the temperature is homogenized throughout the fish.
- According to current regulations, The center of the food must reach 60°C for at least one minuteIf the piece is thick, it will take longer to reach the centre of the food. The time of exposure to heat will depend on the temperature, since if it is higher, we can cook it for less time, as long as we ensure that the heat reaches the centre of the food. As a guide, AESAN tells us that a piece of about 2.5 centimetres thick should be cooked for 10 minutes in total (turning it over after 5 minutes).
- In the case of freezing, the legislation specifies that Freezing must be kept for at least 5 days at a temperature below -20°C. You have to take into account the time that passes between placing the piece in the freezer and the time it takes to freeze to the center of the food.
- Freezing temperature is not the same as freezing storage temperature. That is, when it comes to Freezing fish should be done as quickly as possible at the lowest possible temperature. (ideal between -20 and -24°C).
- Not all home freezers reach these safe temperatures.. -20°C is only reached in refrigerators with three stars (***) or more. If our refrigerator has less than three stars, food safety authorities recommend always buying fish already frozen.
- It is not necessary to freeze fresh fish systematically. Whether or not to do so will depend on how we are going to consume it.
This is how anisakis allergy is treated.
If the allergy is caused by contact with the live larva, the treatment is the same as for other allergies: avoid the antigen. This means that those with allergies should abstain from eating fish, provided that their allergist advises them to do so.
The expert reminds us that it is especially important to take extreme precautions to cook or freeze fish well when feeding babies. “If they develop an allergy, they may have it for the rest of their lives. This would mean eliminating fish from their diet, which is a very important food for their health and a healthy and balanced diet.”
The ALDI Council
If you are going to buy food containing raw fish, such as sushi and sashimi, always buy it from trusted establishments. If you are travelling, avoid eating raw or undercooked fish entrails, as they are more likely to contain anisakis larvae.
Carmen FerrerShe is a professor at the Blanquerna Faculty of Health Sciences, where she teaches the following subjects: Bromatology, Microbiology, Toxicology, Food Safety, Collective Catering and Food Technology. She has a degree in Pharmacy from the University of Barcelona, a master’s degree in Nutrition and Food Sciences, is a researcher with a postgraduate degree in Food Safety and a PhD.
