Uni (Sea Urchin), Naotake Murayama from San Francisco, CA, USA, CC BY 2.0 , via Wikimedia Commons

Uni: Everything You Need to Know About Sea Urchin


Sea urchins, commonly called “uni” in culinary contexts, are a group of echinoderms that have captivated researchers and food enthusiasts alike. This article delves into the taxonomy, anatomy, ecology, reproduction, and culinary applications of sea urchins, providing a comprehensive understanding of these intriguing marine creatures.

What is Uni (Sea Urchin)?

Sea urchins, or uni, belong to the class Echinoidea within the phylum Echinodermata. These spiny, globular organisms can be found in nearly every ocean worldwide, inhabiting various depths and environments. With over 900 species documented, sea urchins are a diverse group that has been a subject of interest in scientific research and gastronomy.

Taxonomy and Anatomy

The class Echinoidea is divided into two subclasses: Euechinoidea and Perischoechinoidea. Euechinoidea, the subclass containing the most extant species, is further divided into Cidaroida and Echinoida.

The anatomy of sea urchins is characterized by a rigid, spherical shell called a test composed of calcium carbonate plates. The test is covered in movable spines that function in locomotion, protection, and feeding. 

Sea urchins also possess a unique water vascular system, which facilitates tube foot movement and respiration. The mouth on the underside of the test houses a specialized feeding structure called Aristotle’s lantern, used for grazing on algae and other organic matter.

Ecology and Distribution 

Sea urchins are distributed across diverse marine environments, from shallow coastal waters to the deep sea. They play a crucial role in shaping benthic ecosystems, acting as grazers that control algal populations and contributing to the bioturbation of sediments.

Their diverse ecological roles have also made them the subject of various ecological interactions, such as predation and competition. Predators of sea urchins include sea otters, starfish, and various fish species. In some cases, sea urchins can become overpopulated, leading to destructive grazing behaviours that can devastate kelp forests and other marine habitats.

Reproduction and Development

Sea urchins exhibit external fertilization, wherein females release eggs and males release sperm into the water column, allowing fertilization to occur. Following fertilization, a planktonic larval stage called the echinopluteus develops, which eventually metamorphoses into a juvenile sea urchin, settling onto the benthos to begin its adult life.

The life cycle of sea urchins varies among species, with some demonstrating a rapid growth and reproduction strategy while others exhibit slower growth and greater longevity.

Culinary Applications

Uni, the edible part of a sea urchin, refers to the gonads, which are considered a delicacy in various cuisines. Particularly popular in Japanese, Mediterranean, and Chilean culinary traditions, uni is often consumed raw or lightly cooked. The taste and texture of uni can vary depending on the species, diet, and habitat, with flavour profiles ranging from sweet and creamy to briny and robust.

Recent years have seen a surge in the popularity of uni, driving up demand and creating sustainability concerns. As a result, efforts have been made to develop sustainable sea urchin aquaculture and promote responsible harvesting practices.

What Does Uni Taste Like?

The taste of uni, or sea urchin gonads, can vary depending on the species, diet, and habitat. Uni is generally known for its unique, delicate flavour and creamy, buttery texture. Flavour profiles can range from mildly sweet and briny to rich and oceanic, with subtle umami notes. Some people describe the taste as similar to a raw oyster but with a more custard-like consistency. The freshness of the uni also plays a significant role in its taste; high-quality, fresh uni tends to have a more pleasant, refined flavour, while older or lower-quality uni might exhibit a stronger, fishier taste.

How to Cook Uni

While uni is often enjoyed raw in sushi or sashimi, it can also be prepared in various cooked dishes, enhancing its unique flavour and adding a touch of luxury to your meal. Here are a few ways to cook uni:

  1. Uni Pasta: One popular way to enjoy cooked uni is by incorporating it into a creamy pasta sauce. To make uni pasta, blend uni with butter, garlic, lemon juice, and a touch of cream, then toss it with cooked pasta, such as spaghetti or linguine. Garnish with fresh herbs, such as parsley or basil, and serve immediately.
  2. Uni Scrambled Eggs or Omelette: Uni pairs well with eggs, making it a delicious addition to scrambled eggs or an omelette. Gently fold uni into your cooked scrambled eggs or add it as a filling for your omelette. You can also include other ingredients like sautéed mushrooms, onions, or fresh herbs to enhance the dish.
  3. Grilled or Broiled Uni: Grill or broil uni on the half-shell for quick and simple preparation. Season the uni with a light sprinkling of salt and pepper, and then place it on a preheated grill or under a broiler for just a few minutes until it’s warmed through and slightly firm. Serve with a squeeze of lemon and a side of crusty bread.
  4. Uni Risotto: Incorporate uni into a creamy risotto for a luxurious twist. Prepare a basic risotto using Arborio rice, onions, garlic, and white wine. When the risotto is nearly done, gently fold in the uni, allowing it to cook through and infuse the dish with its rich flavour. Finish with a sprinkle of fresh herbs, such as chives or parsley.
  5. Uni Crostini: Spread a thin layer of softened uni on toasted baguette slices or sourdough bread. Place the crostini under a broiler for a few minutes until the uni is warmed through and slightly caramelized on the edges. Top with thinly sliced scallions or chives and a drizzle of olive oil.

Remember that uni is delicate and can become rubbery or lose its unique flavour when overcooked. Therefore, it’s essential to use gentle heat and keep cooking times relatively short to preserve the uni’s taste and texture.


Sea urchins are fascinating marine organisms with a rich ecological and gastronomical significance. Understanding their taxonomy, anatomy, ecology, and reproduction deepens our appreciation for these unique creatures and informs conservation and culinary practices. As we continue to explore the intricacies of sea urchins, the knowledge gained will be invaluable for preserving marine ecosystems and ensuring the long-term sustainability of uni as a cherished delicacy.

Future research on sea urchins may focus on understanding their responses to climate change, ocean acidification, and habitat degradation, as these factors can profoundly affect their populations and the ecosystems they inhabit. Additionally, further development of sea urchin aquaculture and advancements in stock enhancement techniques may help meet the increasing demand for uni while minimizing the ecological impact of harvesting wild populations.


Are Uni Shellfish?

Uni is not considered shellfish, although it is a marine organism. The term “shellfish” typically refers to aquatic animals that have a shell or exoskeleton, such as mollusks (e.g., clams, oysters, and mussels) and crustaceans (e.g., crabs, lobsters, and shrimp). On the other hand, Uni refers to the edible gonads of sea urchins, which belong to the phylum Echinodermata and the class Echinoidea. While sea urchins have a hard, calcified outer structure called a test, they are not classified as shellfish because they are not part of the mollusk or crustacean groups.

Where Can I Buy Uni?

Uni, or sea urchin gonads, can be purchased from various sources, depending on your location and availability. Some common places to find uni include:

  1. Japanese or specialty seafood markets: Many Japanese markets and specialty seafood shops carry fresh or frozen uni. These stores often have a dedicated seafood section where you can find high-quality seafood products, including uni.
  2. Sushi restaurants: Some sushi restaurants may offer uni as a part of their menu, either as sushi (nigiri or gunkan-maki) or sashimi. It’s essential to choose a reputable sushi restaurant focusing on quality and freshness to ensure the best uni experience.
  3. Online retailers: Several online retailers specialize in delivering fresh or frozen seafood, including uni, to customers. When purchasing from an online retailer, ensure that they have a good reputation for quality and use proper shipping methods to maintain the freshness and integrity of the uni during transit.
  4. Local fishmongers or seafood markets: Depending on your location, some local fishmongers or seafood markets may carry uni. Availability might be limited or seasonal, so it’s a good idea to call ahead and inquire about their current stock.
  5. Sea urchin festivals or events: In some coastal regions where sea urchins are harvested, you may find annual sea urchin festivals or events where freshly caught uni are available.

When purchasing uni, it’s crucial to prioritize freshness and quality, as these factors significantly impact the taste and overall experience. Fresh uni should have a vibrant colour (ranging from light yellow to bright orange) and a firm yet creamy texture.

What is Uni Butter?

Uni butter is essentially butter with uni or sea urchin gonads incorporated into it. Uni butter may also add additional seasoning and aromatics to enhance its flavour.

Is Uni Good For You?

Uni, or sea urchin gonads, can be considered nutritious when consumed in moderation. It is rich in several nutrients and provides some potential health benefits:

  1. Protein: Uni is a good source of high-quality protein, which is essential for the growth, repair, and maintenance of body tissues, as well as immune system function.
  2. Omega-3 fatty acids: Sea urchin gonads are rich in omega-3 fatty acids, particularly EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). These essential fatty acids support heart health, reduce inflammation, and promote brain function.
  3. Vitamins and minerals: Uni contains various vitamins and minerals, such as vitamin A, vitamin E, and vitamin B12, as well as minerals like zinc, copper, and selenium. These nutrients are crucial in maintaining overall health and supporting various bodily functions.
  4. Low in calories: Uni is relatively low in calories, which can benefit individuals who are watching their calorie intake or trying to maintain a healthy weight.

However, it is essential to consume uni in moderation, as it is also high in cholesterol. However, dietary cholesterol does not have the same impact on blood cholesterol levels as saturated and trans fats. Individuals with high cholesterol levels or a history of heart disease may need to limit their intake.

Additionally, it’s crucial to ensure that the uni you consume is fresh and of high quality to minimize any potential risks associated with consuming raw seafood, such as foodborne illnesses or exposure to contaminants.

Can You Eat Uni While Pregnant?

Pregnant women are generally advised to avoid consuming raw or undercooked seafood, including uni, due to the risk of foodborne illnesses caused by bacteria, parasites, or viruses. Foodborne infections, such as listeriosis and toxoplasmosis, can lead to severe complications during pregnancy, affecting both the mother and the developing fetus.

Some medical professionals and guidelines also recommend that pregnant women limit their consumption of certain types of fish and shellfish, due to concerns about mercury exposure. While sea urchins are not specifically known for high mercury levels, it is still essential to exercise caution and prioritize safety during pregnancy.

If you are pregnant and craving uni, you may consider other cooked seafood options low in mercury and safe for pregnant women, such as salmon, shrimp, or light canned tuna. Always consult your healthcare provider or a registered dietitian for personalized advice and guidance on dietary restrictions and recommendations during pregnancy.

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