Fish roe are the fully ripened eggs of many types of fish, including sturgeon, salmon and herring.

Masago is the roe of capelin, a small fish found in the cold waters of the North Atlantic, North Pacific and Arctic oceans.

A popular ingredient in Asian cuisine, masago is considered a specialty product — sought after for its distinct taste.

This article looks at the nutrition, benefits, downsides and uses of masago.

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Smelt roe — commonly known as masago — are the edible eggs of the capelin fish (Mallotus villosus), which belong to the smelt family.

They’re considered a forage fish — meaning they are an important food source for larger predators, such as codfish, seabirds, seals and whales.

These small, silvery-green fish closely resemble sardines.

Though the flesh of capelin is edible, it’s most sought after by fishermen to create other products, including masago.

About 80% of harvested capelin is used to produce fishmeal and fish-oil products, while the remaining 20% is used to produce masago (1).

Female capelin begin releasing eggs at around two to four years of age and continue spawning until their death.

Masago is harvested from female capelin when the fish are full of eggs but before they have the chance to spawn.

It’s smaller in size and less expensive than the popular tobiko (flying fish roe) and is commonly used as an ingredient in sushi rolls.

Fresh masago has a pale yellow color and is often dyed bright hues — such as orange, red or green — to add visual interest to dishes.

It has a mild flavor and is sometimes mixed with ingredients including wasabi, squid ink or ginger.

Summary Masago is harvested from female capelin fish before they have a chance to spawn. It’s commonly used as an ingredient in sushi and often dyed to add visual interest to dishes.

Like other types of fish roe, masago is low in calories but high in many important nutrients.

Just 1 ounce (28 grams) of fish roe contains (2):

  • Calories: 40
  • Fat: 2 grams
  • Protein: 6 grams
  • Carbs: less than 1 gram
  • Vitamin C: 7% of the Reference Daily Intake (RDI)
  • Vitamin E: 10% of the RDI
  • Riboflavin (B2): 12% of the RDI
  • Vitamin B12: 47% of the RDI
  • Folate (B9): 6% of the RDI
  • Phosphorus: 11% of the RDI
  • Selenium: 16% of the RDI

Fish roe is particularly high in vitamin B12, an essential nutrient that you must get from the foods you eat, as your body cannot produce it on its own.

B12 is critical for many functions, including red blood cell development, energy production, nerve transmission and DNA synthesis (3).

Fish roe like masago is low in carbs but rich in protein and healthy fats like omega-3 fatty acids.

These polyunsaturated fats help regulate inflammation and are vital for the proper function of your immune system, heart, hormones and lungs (4).

Additionally, fish roe is packed with amino acids — the building blocks of protein — especially glutamine, leucine and lysine (5).

Glutamine plays important roles in intestinal health and immune function, while leucine and lysine are essential for protein synthesis and muscle repair (6, 7).

Summary Fish roe is low in calories yet high in nutrients like healthy fats, protein, vitamins and minerals.

Like other types of seafood, masago is nutritious and offers a variety of health benefits.

A Rich Source of High-Quality Protein

Though tiny in size, masago packs a powerful punch of protein.

A single 1-ounce (28-gram) serving delivers 6 grams of high-quality protein — about the same as one large (50-gram) egg (8).

Protein is the most filling of all nutrients, followed by carbs and fat.

Adding protein-rich foods like masago to your diet can help you stay satisfied and prevent overeating, which could lead to weight loss (9).

Fish roe is a complete protein, meaning it has all nine essential amino acids your body needs.

A Natural Source of Selenium and Vitamin B12

Masago is a good source of selenium, a mineral that acts as a powerful antioxidant in your body.

Found in concentrated amounts in seafood, selenium reduces oxidative stress and plays critical roles for your thyroid and immune system (10).

Research shows that increased blood levels of selenium may enhance immune response and prevent mental decline (11, 12).

Masago is also high in vitamin B12, which is critical for nerve health and energy production, as well as other important bodily functions (13).

High in Omega-3 Fatty Acids

Omega-3 fats are polyunsaturated fats with many powerful health benefits.

These special fats regulate inflammation, control blood clotting and are an integral part of your cell membranes.

Research indicates that higher dietary intake of foods rich in omega-3 fats is associated with a lower risk of heart conditions, including heart failure and coronary artery disease (14, 15).

Fish and fish products like masago are some of the best dietary sources of omega-3 fats.

Low in Mercury

Because capelin is a small forage fish, it tends to be much lower in mercury than larger fish like mackerel and swordfish.

What’s more, research shows that fish roe tends to be lowest in mercury when compared to other parts of the fish like organs and muscle tissue (16).

For this reason, fish roe like masago can be safely consumed by those who want to keep their mercury exposure to a minimum.

Summary Masago is high in important nutrients like protein, vitamin B12, selenium and omega-3 fats, which may offer various health benefits. In addition, it’s low in mercury, allowing you to limit your exposure to this heavy metal.

Though masago offers some health benefits, it has potential downsides as well.

Ecological Concerns Over Capelin Fishing

While masago may be a better choice than other types of seafood, buyers should be aware of some concerns over bycatch of endangered and overfished species related to capelin fishing methods.

Environmental organizations express uncertainties over capelin populations and concerns over certain fishing methods (17).

As egg-bearing female capelins are often targeted to support the demand for masago, some environmental groups worry that this method may negatively impact the species’ population over time (18).

High Sodium Content

Like most other fish roe, masago is high in sodium.

What’s more, masago is often mixed with salty ingredients — such as soy sauce and salt — to enhance taste, which increases the sodium content of the final product.

Some brands of masago pack in over 260 mg of sodium — 11% of the RDI — into a tiny 1-teaspoon (20-gram) serving (19).

Though most people don’t need to follow a low-sodium diet, excess salt consumption may negatively impact health and can lead to increased blood pressure in salt-sensitive people (20, 21).

Risk of Allergic Reaction

Since masago is a seafood product, those who are allergic to fish and shellfish should avoid it.

Fish roe contains vitellogenin, a fish egg yolk protein identified as a potential allergen (22).

What’s more, fish roe can even cause allergic reactions in people without seafood allergies. These include rashes, narrowing of the airways and low blood pressure (23).

In Japan, fish roe is the sixth most common food allergen (24).

Can Be Combined With Unhealthy Ingredients

Many companies combine masago with unhealthy ingredients, such as high-fructose corn syrup and monosodium glutamate (MSG).

Regular consumption of high-fructose corn syrup is linked to weight gain, insulin resistance and inflammation (25).

MSG is a common food additive used to enhance flavor in products like masago.

Research shows that MSG may lead to adverse reactions in some people, such as headache, weakness and flushing of the skin (26).

Summary Masago may be high in sodium and contain unhealthy ingredients like MSG and high-fructose corn syrup. Additionally, certain capelin fishing methods raise ecological concerns.

Masago is a unique ingredient that can be used in a number of ways.

Its semi-crunchy texture and salty flavor make it a perfect addition to Asian-inspired dishes or appetizers.

It can be purchased through numerous seafood vendors in many different flavors, such as ginger, wasabi and squid ink.

Here are some ways to add masago to your diet:

  • Top homemade sushi rolls with a few teaspoons of masago.
  • Combine masago, cheese and fruit on a plate for a tasty appetizer.
  • Use masago to flavor rice dishes.
  • Spoon masago onto poke bowls for a unique topping.
  • Add masago to Asian noodle dishes.
  • Top fish with masago for a flavorful recipe twist.
  • Mix masago into wasabi or spicy mayonnaise to flavor sushi rolls.

Because masago is usually high in salt, you only need a small amount to create a powerful punch of flavor.

Though it’s most often used in Asian cuisine, masago can be incorporated into many recipes that would pair well with something salty.

Summary Masago can be added to Asian dishes like noodles, rice and sushi. It can also be incorporated into dips and used as a topping for fish.

Masago or smelt roe are the edible eggs of the capelin fish.

They’re loaded with protein and nutrients like omega-3s, selenium and vitamin B12.

Avoid products that contain unhealthy ingredients like added salt, high-fructose corn syrup or MSG, and don't eat masago if you're salt-sensitive or allergic to seafood.

However, if you can tolerate seafood and are looking for an interesting ingredient that will add a distinct flavor to your recipes, give masago a try.