Can I Make Sushi From Freshly Caught Fish?

Now that you have brought your fresh catch home, it’s time to prepare it. You have a hankering to make some sushi, but is it wise to make sushi from freshly caught fish?

You can make sushi from freshly caught fish, but only after you have frozen the fish. However, the freshly caught fish needs to be frozen at temperatures lower than your freezer to kill parasites. Dry ice will get your catch cold enough to kill them. 

Sushi made from commercially caught fish is safe, but your catch might not be. Let’s find out the dangers and what you can do to make your fish safe to eat.

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The Dangers of Making Sushi From Freshly Caught Fish

Unfortunately, sushi from truly fresh fish can be unsafe and unhealthy. It’s a shame because of the benefits of raw fish. Not only does fried fish add calories, but it also destroys some of the fish’s Omega 3 acids. Fried or grilled fish also has an increased level of heterocyclic amines, which have been linked to a higher risk of cancer.  

The risks can be grouped into three categories—pollutants, bacteria, and parasites.  

Pollutants

If you think that polluted waters are a thing of the past, think again. An EPA study of 500 random lakes and rivers found that mercury was detected in all fish samples. Half of the fish contained levels of mercury that were greater than EPA recommendations. Additional studies continue to show high mercury levels.

The United States has spent millions of dollars cleaning our waterways, so why are they still polluted? Partially, we have successfully reduced what is known as point source pollution—contamination from one source. However, reducing pollution from multiple sources—agricultural and stormwater runoff, for example—is more challenging.

The good news for sushi lovers is that scientists have identified the people most at risk from pollutants—children, pregnant women, and older people with serious health concerns. If you are eating fish daily—raw or not—and you begin to notice signs of mercury poisoning, like blurred vision, foggy thinking, balance problems, and tremors, you should see a doctor.

Bacteria

Not all bacteria are harmful, but the ones that are can cause us to become sick. These harmful bacteria are called pathogens. E. coli, listeria, and salmonella are the most common ones. Most of the symptoms are gut-related—diarrhea, stomach cramps, upset stomach—and will pass several days.  

Bacteria more specific to raw fish, including norovirus and Vibrio vulnificus, can be potentially more dangerous. If you have difficulty breathing, bleeding in the skin, or severe abdominal issues, contact your doctor.

However, most bacterial infections will clear themselves up within a few days and are not nearly as problematic as parasites. 

Parasites

Parasites, like bacteria, are everywhere. Some parasites can be seen. If there’s a worm in an apple, you cut out that part of the apple (or throw the whole thing away). However, unless you have experience candling freshly caught fish, it is likely you will not see the parasites. Killing off the parasites is simple—cook the meat. Cooked fish rolled in Nori might taste good, but it is not sushi.  

We can be infected by two types of parasites—tapeworms and roundworms.  

There are several species of roundworms, so they are often called nematodes, or Anisakiasis. Roundworms get into our food via seals or sea lions who eat fish infected with them. The larvae roundworms grow to maturity in the guts of the seal or sea lion, who then excrete the roundworm eggs, which get eaten by crustaceans. Fish eat the crustaceans, we eat the fish, and that’s how the roundworms wind up in our guts.

Tapeworms have a similar life cycle, except the process occurs in freshwater. 

Does the Type of Fish Make a Difference?

Fish near the top of the food chain tend to have higher mercury levels and other toxins. Tuna, sharks, and swordfish can contain unsafe levels of mercury. If you fish in the Gulf of Mexico, avoid King Mackerel and Tilefish. 

When it comes to mercury, the good news is that many fish in the United States, including catfish, cod, flounder, pollock, and salmon, have low mercury levels.

Does Where the Fish Is Caught Make a Difference?

Yes, it does.  

Freshwater fish such as perch and pike can infect a person with tapeworms. Some studies have shown that 50% or more of the northern pike have tapeworms. The general advice is that you should be extremely cautious about eating freshwater fish. 

Saltwater fish such as cod, flounder, halibut, pollock, rockfish can contain roundworms. However, saltwater fish such as bluefin, bigeye tuna, mahi-mahi, yellowfin, and wahoo are safe to eat raw.

What You Should Do Before Making Sushi From Fish You Caught

By now, you have undoubtedly asked yourself if my uncooked fish is dangerous, how is it that sushi from a restaurant or grocery store is safe?  

What makes a restaurant and store-bought sushi safe is what happens after it is caught. Instead of rushing it to market, the fish is first frozen. Parasitic worms are killed when frozen—but not frozen like tossing the fish into a household freezer. To be commercially frozen, the fish needs to be flash-frozen at temperatures much lower than a household freezer.

To kill off parasites, fish caught at sea is frozen at -35 to -40 °F (-37 to -40 °C) for at least 14-15 hours. The average home freezer is set in the 0 to 10 °F (-17 to -12 °C) range, not long enough to kill parasites. Even if you could get the temperature in your freezer to -5 °F (-21 °C), you would have to wait for seven days to guarantee all parasites have been killed.

Luckily, you can recreate the temperatures of commercial fishing by using dry ice.

What Is Dry Ice and How Can I Use It?

Dry ice is solid carbon dioxide. We exhale carbon dioxide as a vapor or gas, but it becomes solid when it reaches -109 °F (-78 °C). This means that when you buy dry ice, your product starts off at temperatures well below those required to kill off parasites.  

If you have never used dry ice before, you need to be careful. It is not the same as handling ice cubes. Look out for these dangers:  

  • Frostbite: If you touch dry ice for more than a few seconds, you can sustain frostbite. Handle dry ice with leather gloves, oven mitt, or a thick towel. Treat frostbite just like any other burn. Apply some antibiotic ointment for a minor “burn.” If you have blistering skin or peeling skin, then you should contact your doctor.
  • Suffocation: As dry ice sublimates (turns back into a gas), the carbon dioxide can make enclosed spaces dangerous. This is especially true in small spaces, such as cars. When transporting dry ice in a car, make sure you have adequate ventilation. If you begin to breathe heavily, get a headache, or have your nails or lips start to turn blue, you need to get fresh air immediately.
  • Explosion: Storing dry ice in an airtight container can lead to danger because, as dry ice sublimates, it expands. This could cause a cooler to expand and possibly explode.

Warning: Do not store dry ice in your freezer as it will turn off the thermometer. On the other hand, if you lose power, dry ice will keep food cold longer.

Dry ice sublimates at the rate of 5 to 10 pounds (2.3 to 4.5 kgs) per 24 hours from the time it is created. A 10-pound (4.5-kgs) slab of ice will last you a day, long enough to kill off parasites.

Do You Wash Fish Before Making Sushi?

Once you catch your fish, you need to eliminate any bacteria that might be on the fish. There are several methods to do so:

  • A common bacteria found on seawater fish, Vibrio parahaemolyticus, can be a cause of gastroenteritis. Since freshwater will kill it, you could rinse the fish’s skin and scales.   
  • If you plan to keep the skin on, then pour boiling water over the filets after you have cleaned the fish.  
  • Searing fish like bonito is another method used to kill bacteria. 

In sushi, cleanliness is essential, so any steps you can take, including washing your fish, your knives, and surfaces on which you’ll be working, will go a long way to killing off bacteria and parasites. 

Bottom Line

If you want to make sushi from fish you catch, you need to use the method commercial fishermen use—flash freeze your catch using dry ice. That is the only way to kill the bacteria that could be in the fish.

Sources

What Do You Need to Make Sushi?

How to Make Sushi Without Seaweed