Fish Parasites: Dealing with Parasites for Sushi

Tony
9 min readAug 6, 2020

How Likely Is It to Get Parasites From Sushi?

Fish parasites in sushi sashimi is the worst nightmare for any sushi or sashimi lover. The worries of having parasites in the sushi I eat entered my perspective recently when I read a news article. It was about a man who had contracted such a problem from eating raw sashimi everyday.

In actuality the odds of contracting such parasites are extremely unlikely in America under the increasing regulation from the US Centers for Disease Control and Prevention.

Additionally sushi that is made from fish has undergone a process called flash freezing before freezing more in a commercial freezer.

Flash Freezing is a very effective measure for killing parasites in sashimi, because it keeps the fish frozen at temperatures below -31 degrees Fahrenheit or lower.

Additionally, this source explains how at a temperature of minus 31 degrees for 15 hours is enough to kill the parasites that live in the meat.

According to the USDA, “ Parasites can be destroyed by sub-zero freezing temperatures…cooking, however, will destroy all parasites.”

What Temperature Will Kill Parasites in Sushi?

While researching online I found an FDA paper for the best ambient freezing temperatures, and length of time for dealing with parasites like Anisakis or Diphyllobothrium tapeworms and other parasites:

  • -4 Degrees Fahrenheit or -20 Degrees Celsius and freeze for a total of 7 days
  • Below -31 Degrees Fahrenheit or -35 Degrees Celsius and freeze the fish for at least 15 hours
  • For most parasites an ambient temperature of -4 Degrees Fahrenheit or below for 24 hours is sufficient.

The length of time and the right temperature is flexible in accordance with how big the fish meat is. It is important how well the temperature is able to “equalise within the meat”.

How Well Is Curing for Preventing Parasites in Fish Meat?

While, salt curing for preventing fish parasites has been part of many cultures around the world as a measure for preserving the fish and decreasing chances of parasite infection.

The problem with treating parasites that are in fish meat, is that not one prevention can always by itself fully ensure against having parasites that may still be living in the fish meat.

My research shows certain doubts to the effectiveness of salt curing for killing parasite infections in the fish. In fact, curing may be of only low effectiveness in comparison with the use of high heat or using low freezing temperature.

While the first source was only an experiment for ham, it also shows there wasn’t a high correlation for curing (dried or smoked) to be able to inactivate the parasite trichinae.

On a second source, an experiment was done using dry-curing on the meat of pigs to test its effects on the parasite T. gondii, which can cause an infection that results in fever and muscle pain.

Contrastingly with this second experiment the dry curing had a more positive effect, and produced hams that could be “consumed without significant health risk”.

Which leaves the idea of the actual ability of curing meat to prevent parasites a little vague in terms of risk.

Conclusively, curing does present a slight ability to reduce parasites in ham meat and may also produce similar effectiveness for killing parasites in fish meat. However, it is wise for the reader to use further safety measures.

Using Heat to Prevent Fish Parasites

Another way to kill fish parasites is to cook the fish with high heat, since parasites have a hard time surviving in high temperatures and a cooking temperature of at least 145 degrees Fahrenheit for 15 seconds, it is hot enough to kill most parasites that are found in sashimi.

Some technical factors in kitchen stovetops may vary, but the temperature for the lowest heat setting is generally around 150–200 degrees. While the ‘high’ setting on the stove-top would create a temperature of 425–500 degrees Fahrenheit.

With high temperature and long duration of cooking, it is safe to say that parasites that are found in sushi sashimi are already killed by the time the food is served.

However, in order to be certain, it is best that every part of the salmon or other fish is fully cooked. Therefore, cooking every part of the sashimi for a long duration at a high temperature above 145 degrees is safer.

How Do Chefs Remove Parasites in Sushi?

This information about freezing and cooking the fish sashimi for sushi might be useful at home but what if you’re eating at a restaurant?

Recently there’s been some news on how parasites found in raw or undercooked seafood have increased 283 fold in the past 40 years,

but this data is false since a published research paper from the National Library of Medicine states that there had only been 24 cases of anisakiasis (a common worm parasite) reported in a total of 13 years.

A high rate of parasite worm infection is more prevalent in places like Africa, and some Asian countries where people are eating raw fish that has not been commercially frozen or fully cooked.

With that said, chefs cannot totally remove by hand all the worm parasites in a large fish, because the parasites might be deep inside the meat or are barely perceptible with the eyes.

That’s why having preventative measures like cooking the fish or freezing at a low temperature is a good idea, because you just don’t know where the worm parasites hide.

If you’re living outside the US or have other worries, be sure to only eat from restaurants that have a nice reputation for their food. Give a call to make sure the restaurant keeps its hygiene.

Does Farmed Raised Fish Have Less Parasites?

Firstly, farmed sushi fish are raised with chemicals, medication, and other treatments for preventing parasites makes it less likely to find worms in them.

From an article in the Journal of Zoology, a group of scientists did an experiment using an anesthetic chemical on a group of fish which resulted in 26–31% fewer lice in normal fish.

Looking from a grand scale of things, this method of using harsh chemical treatments on farmed sushi fish is not great for the welfare of these animals.

Moreover, it is simply difficult and even impossible to contain certain parasitic outbreaks for some crowded cage aquaculture in the world. Especially for Norway which has the biggest fish cage that stores well over 1 million fish according to a source from futurity.org.

Increasing the use of harsh chemicals on farmed fishes for better effectiveness for preventing parasites may also create unforeseeable problems for our ocean environment cited from this post.

Despite concerns for wild caught sushi fish, the incident rate is actually very low annually. Wikipedia states that the reported cases of parasitic infection by wild fish is fewer than 40 cases per year in the U.S.”

With numerous precautions such as boiling, burning, curing with salt, or flash freezing is able to decrease the chances of incident rates by the time the food is served for diners.

Where Are Parasitic Infections Most Common?

Parasitic infections are common in many different places and are not confined in one specific area.

This research points to the fact that it is most prevalent in low and middle income countries because humans have a higher possibility for eating contaminated meat.

For intestinal parasites such as heartworm, roundworm, or tapeworm in the year 1995. This information states that there were higher rates overall in Africa(5.7%) and Asia(3.8%).

In another study done, one group of children below 5 years old in different parts of Ethiopia found that there were 26.6% rate of parasitic infection in the southern parts of the area.

The high statistics of infection were not due to eating unclean meat. Instead, it was correlated with the children’s poor hand washing that causes them to be more vulnerable to such infections.

Does Raw Ginger or Garlic Prevent Sushi Parasites?

Numerous researches have shown positive effectiveness of garlic and ginger for inhibiting bacterial growth.

Ginger is most helpful for inhibiting the growth of bacterias from eating sushi fish. And is effective for aiding digestion or providing nutritional benefits.

In Japan raw ginger is used as a palate cleanser for reducing the fishy flavor of the sashimi in the mouth and additionally for its refreshing taste. It shows no ability for combatting potential issues with parasites in sushi fish.

However, the usage of garlic actually proves in an experiment on lambs to be able to substantially assist in lowering the prevalence of the parasite called Acanthocephalan to 20% through taking 200mL/kg of garlic.

While this article points to the property of Allicin in garlics exhibiting antibacterial activity and as well affecting in a beneficial way against many intestinal parasites. Additionally, it can also be used to treat other parasites like hookworm or tapeworms in humans.

Does Sushi Grade Fish Have Less Parasites?

Firstly, don’t eat fish or other seafood raw even if they are bought in a reputable place unless it is stated that it can be eaten raw. So look for a tag or find a way to make sure that it is safe for being eaten as sashimi.

Secondly, the title of sushi grade on a fish doesn’t guarantee that the sushi fish is safe to eat raw without chances of being infected with dangerous parasites.

This is more of a marketing term that is up to the seller’s interpretation as to the quality and safety of the fish. Unless you really trust the guy selling you the fish for sushi, then the grade of fish is really meaningless.

The term sushi grade has more significance if you’re looking to buy high quality and expensive cuts of certain parts of a sushi fish.

If you’re simply buying a regular sushi fish for sashimi, then it is best you make sure that the seller is selling you a ‘safe’ fish that has been carefully freezed at low temperatures before it arrives to be bought at the market.

For an additional safety measure, cook the fish at high temperatures thoroughly to kill off all bacterias and parasites that might exist in the meat.

Does Vinegar Kill Parasites in Raw Fish?

Vinegars that are bought in supermarkets generally contain 5–8% acetic acid per volume. For example, a bottle of apple cider vinegar contains %5 to 6% acetic acid.

A 5% concentration of acetic acid has demonstrated high effectiveness for killing all life in the eggs of parasites such as Ascaris, a type of hookworm, in 30 minutes.

As well as another group of experiments where scientists bathed live fishes with parasites in 4% acetic acid vinegars were able to again show effectiveness for using vinegar for destroying parasites without harming the fish with the high acid level.

Considering these interesting results, maybe the ancient Japanese chefs were onto something when they placed their raw fish among vinegared sushi rice.

It Is Easy to Spot Parasites in Sushi Fish?

A sushi lover’s worst nightmare is to see a tapeworm wriggling in their sushi as they are about to take a bite. Luckily such encounters are really rare in countries with strict food regulations.

With safety measures that had been recommended in this post, readers shouldn’t be worried at all if any or all the tips are applied the next time before going to a restaurant or cooking at home.

The known parasites by most people are such fish parasites like tapeworms or hookworms. In reality, the parasites that exist in fish caught in the ocean are often more microscopic than that.

Researching this topic I discovered an article that states there are three main classes of parasites:

  1. Ectoparasites– this includes parasites that are usually of larger size like salmon lice, mites, and ticks
  2. Helminths– these are smaller sized parasites than Ectoparasites and a name for parasitic worms like tapeworms, nematodes, or flukes
  3. Protozoa– such parasites are really small and can only be seen with microscopes. Protozoa parasites include those that cause malaria, white spot disease in fish, as well as African trypanosomiasis.

While some parasites like salmon lice or tapeworms can be easily identified on the fish and avoided. A higher risk of parasitic infections comes from the lack of hygiene in terms of how the sashimi is prepared, which creates bacteria in the food served.

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