Can you eat swordfish raw?

In this article, we will answer the question “Can you eat swordfish raw?” and discuss the risks of eating swordfish raw. Swordfish fishery is one of the most important fishing activities in the Mediterranean Sea, in particular in South Italy.

Can you eat swordfish raw?

Yes, you can eat swordfish raw. However, it is not recommended. The consumption of seafood contaminated with toxins or infectious agents can cause illnesses ranging from mild gastroenteritis to life-threatening syndromes. 

Seafood is responsible for a significant portion of food-borne illness worldwide. The consumption of raw or undercooked fish is a health risk, especially in the case of pregnant and elderly (1,2).

What are the risks of eating swordfish raw?

The risk of eating swordfish raw is that fish can carry pathogenic microorganisms and parasites. The ingestion of food contaminated with pathogens is a risk to health and may cause foodborne diseases.

To date, over 40 species of parasites associated with seafood, including protozoa, cnidarians, tapeworms, flukes, roundworms, and thorny-headed worms, have been reported in humans (1).

When preparing various kinds of fish, the basic guideline is to cook them until the flesh is opaque and flaky, and may be easily separated with a fork. The cooking temperature may reach 145°F or 74°C (2). 

Consumption of seafood contaminated with toxins or infectious agents can cause illnesses ranging from mild gastroenteritis to life-threatening syndromes (3). 

What are the benefits of eating swordfish raw?

The benefits of eating swordfish uncooked are the many nutrients provided by the fish, which are better preserved, as compared to cooked fish.

Thermal treatments, such as cooking, boiling and drying cause leaching of proteins, hydrolysis of fatty acids and denaturation of vitamins. This causes the reduction of the nutritional benefits offered by the consumption of fish. 

Fish is an important source of many nutrients, including high digestible proteins with improved biological value, minerals, such as calcium, zinc and selenium; and vitamins, including vitamin B12 and niacin. 

In addition, it contains omega-3 polyunsaturated fatty acids, which are related to several health benefits, including anti-inflammatory effects and their protective effects against cardiovascular disease. 

Fish also contains vitamin D and calcium, both necessary to prevent osteoporosis and improve bone health. Moderate-to-high intake of fish has been associated with a decrease in the prevalence of chronic diseases associated with obesity, namely CVD, diabetes and some cancers (4).

Cooking fish can reduce the amount and quality of proteins and lipids. Heat treatments applied to food may have negative effects on lipids, such as hydrolysis of triacylglycerides and phospholipids, producing free fatty acids that are more susceptible to oxidation.

As reported in a study, cooking reduced total lipid levels by 13–26% in mackerel and increased the levels of free fatty acids, which may accelerate oxidation reactions. Thermal treatments reduced the amounts of omega-3 fatty acids as well as of carotenoids.

Although cooking improves the extraction of proteins, it reduces its amounts in fish. Cooking reduced protein by 29% in cooked mackerel compared to this fish raw (7).

Therefore, in order to obtain the most benefits of the omega-3 fatty acids and other nutrients of swordfish, you should eat it raw. 

What are the benefits of cooking swordfish?

The benefits of cooking swordfish are related to the reduction of the levels of heavy metals in the fish, when compared to the raw fish.

As a predator fish, swordfish often contains high levels of mercury and other heavy metals in its composition (4). Although it has been reported that cooking is not able to reduce the levels of mercury in fish, it makes it less bioavailable (8).

Mercury is converted into methylmercury and the accumulation of this toxin in vital organs of the human body such as kidneys, liver, and especially the brain, can cause a variety of pathologies, including cardiovascular, renal, reproductive, and neurological disorders (6). 

It is also possible to reduce the levels of these heavy metals by cooking the fish, as reported in a study. 

The use of heat during cooking can lead to the denaturation of metalloproteins and de-methylation, which can reduce the bioaccessibility of heavy metals. As a result, some heavy metals may be removed during the cooking process. 

However, there is a risk that the free metals can leach into the cooking broth, which is negative in the case of preparing a fish soup. On the other hand, the levels of mercury were not reduced through cooking.

Cooking seafood can decrease the amount of bioaccessible mercury (Hg) in comparison to raw seafood. The intensity of the cooking process determines how much less bioaccessible the Hg is after cooking. 

From most to least bioaccessible, the order of cooking treatments would be raw, steamed/boiled, grilled, and fried. Boiled and fried fish have 40% and 60% lower total Hg bioaccessibility, respectively, compared to raw samples of Spanish mackerel, cat shark, and red tuna. MeHg bioaccessibility was reduced by 75%-96% for grouper and 29%-77% for rabbitfish when steamed, grilled, or fried, compared to raw (8).

How to safely prepare Swordfish?

To safely prepare Swordfish, you should be able to follow good hygiene practices by handling and cooking the fish, in order to reduce its microbial contamination and to avoid further contamination.

Fish can carry microorganisms and parasites and therefore should be carefully chosen, handled and cooked. In addition, fish should be kept under refrigeration during transportation and storage, while by freezing fish, temperature fluctuations should be avoided.

When buying fish, it’s important to look for certain qualities. Fresh fish should have a pleasant, mild odor rather than a strong fishy, sour, or ammonia-like smell. The eyes of the fish should be clear and shiny, indicating that it’s still fresh. 

When looking at the whole fish, check that the flesh is firm and the gills are red without any odor. For fresh filets, the flesh should also be firm and have red blood lines or red flesh for tuna. Additionally, the flesh should bounce back when pressed and there should be no discoloration, darkening, or drying around the edges of the filets (2).

Refrigeration of fish is to be carried at 40°F or 4°C for a maximum period of 2 days. When preparing, wash hands, cutting boards, dishes, utensils, and countertops with soap and hot water before and after the preparation. Cook at a temperature of 145°F or 74°C till the flesh is clear and easily separable with a fork.

The proper selection, storage, preparation and cooking of fish is crucial to avoid the ingestion of contaminated fish, which can lead to food poisoning. The common symptoms of food poisoning are vomiting, diarrhea, and abdominal pain, and flu-like symptoms, such as fever, headache, and body ache.

Conclusion

In this article, we answered the question “Can you eat swordfish raw?” and we discussed the risks of eating swordfish raw.

Reference

1. Shamsi, Shokoofeh. Seafood-borne parasitic diseases: A “one-health” approach is needed. Fishes, 2019, 4, 9. 
2. United States Department of Agriculture. Selecting and Serving Fresh and Frozen Seafood Safely.
3. Shamsi, Shokoofeh. Seafood-borne parasitic diseases: A “one-health” approach is needed. Fishes, 2019, 4, 9.  
4. Gil, Angel, and Fernando Gil. Fish, a Mediterranean source of n-3 PUFA: benefits do not justify limiting consumption. Brit J Nutr, 2015, 113, S58-S67.
5. Delbarre-Ladrat, Christine, et al. Trends in postmortem aging in fish: understanding of proteolysis and disorganization of the myofibrillar structure. Crit rev food sci nutr, 2006, 46, 409-421.
6. Barone, Grazia, et al. Levels of mercury, methylmercury and selenium in fish: Insights into children food safety. Toxics, 2021, 9, 39.
7. Toyes-Vargas, Eduardo, et al. Changes in fatty acids, sterols, pigments, lipid classes, and heavy metals of cooked or dried meals, compared to fresh marine by-products. Animal Feed Sci Technol, 2016, 221, 195-205.  
8. Bradley, Mark A., Benjamin D. Barst, and Niladri Basu. A Review of Mercury Bioavailability in Humans and Fish. Int J Environ Res Public Health, 2017, 14, 2.