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Uni sushi
Uni, considered a delicacy around the world, is the Japanese word for sea urchin, written in kanji as 海胆 (Tabimori 2015, "What is Uni Sushi?"). Anatomically, uni refers to the gonads of the sea urchin - the only truly edible bits. Depending on regional availability and preferences, Japanese uni can traditionally be prepared from many species of urchins. Furthermore, depending on the species and environmental conditions the animal grew up in, uni can vary considerably, ranging in color (from pale yellow to orange), flavor (from saltier to sweeter), intensity of flavor, size, and texture. Good quality uni was historically very seasonal, with certain species only being good to eat at certain times of year, though with modern aquaculture and commercial imports, high quality uni can now be enjoyed year round (Tabimori 2015, "What is Uni Sushi?"). Today, the two most common and highly prized types of Japanese uni are Ezobafun uni and Kitamurasaki uni (Sushipedia 2022).
Traditional Uni
Ezobafun uni | 蝦夷馬糞雲丹
Strongylocentrotus intermedius
With a rich and fine melt-in-your-mouth texture, strong umami flavor, and vibrant orange color, Ezobafun uni is one of the most prized and highest quality types of uni. It's distributed along the northern parts of Japan, ranging from the Tohoku region to Hokkaido. These urchins are up to twice as large as Bafun uni, reaching over three inches in diameter. Ezobafun uni and Kitamurasaki uni are so sought after that, together, they make up 3/4 of Japan's sea urchin catch (Tabimori 2015, "Sushi Visual Dictionary").
Kitamurasaki uni | 北紫海胆
Mesocentrotus nudus
Directly translating to "northern purple sea urchin," Kitamurasaki uni is the other most prized type of uni. Compared to Ezobafun uni, Kitamurasaki uni has a lighter texture and softer flavor, and is known for pairing better with sushi rice. This urchin has a larger distribution range than Ezobafun uni, being found all along the western Japanese coastline (Sea of Japan side), and from the Tohoku region to Hokkaido along the eastern Japanese coastline (Pacific Ocean side). Relatively large, Kitamurasaki uni can grow over three inches in diameter (Tabimori 2015, "Sushi Visual Dictionary").
Murasaki uni | 紫海胆
Heliocidaris crassispina
This species of urchin is the most common to find along the Japanese coast, and makes up 70% of the remainder 1/4 of Japan's urchin catch. It's distribution range extends along most of Japan through the Tonoku region, especially along the eastern side. Murasaki uni is smaller than Kitamurasaki uni, only really growing to two inches in diameter. Because of this, Murasaki uni is not really commercially shipped, even domestically, and is primarily enjoyed locally (Tabimori 2015, "Sushi Visual Dictionary").
Bafun uni | 馬糞雲丹
Hemicentrotus pulcherrimus
'Bafun' directly translates to "horse dung" - a reflection of the urchin's external appearance. While they are not scientifically related to Ezobafun uni, the two species are so visually similar that they are traditionally categorized together (Sushipedia 2022). This species of urchin is found from the southern areas of Hokkaido down to Kyushu. These urchins are quite small, only growing to about 1.5 inches in diameter, making them unfavorable for commercial use. They only make up 25% of the remainder 1/4 of Japan's urchin catch (Tabimori 2015, "Sushi Visual Dictionary").
Aka uni | 赤雲丹
Pseudocentrotus depressus
Aka uni is found in similar regions as the Murasaki uni, so they are often caught together. However, this species of urchin is typically found in deeper waters, making them much harder to catch free diving. Because of this, Aka uni is incredibly rare and expensive, sold only at the most high-end sushi restaurants in Japan. This urchin can grow up to three inches in diameter (Tabimori 2015, "Sushi Visual Dictionary").
Shirahige uni | 白髭海栗
Tripneustes gratilla
Found throughout the Indo-Pacific, including Hawaii, Shirahige uni in Japan are mainly found south of the Kii Peninsula, where the temperatures are warmer. This species of urchin is most significant and well known in the Okinawa region, since this is one of only a few edible urchins that can be harvested in the area. It can grow upwards of three inches in diameter. Shirahige uni has strong umami flavor, comparable to uni harvested in Hokkaido (Tabimori 2015, "What is Uni Sushi?"). 海栗, uniquely used to describe this species, directly translates to "sea chestnut" to reflect the notably shorter and denser spikes covering the test of this urchin.
Modern Imported Uni
Primarily commercially produced and exported from Los Angeles, the red sea urchin is found along the eastern Pacific coastline, from Alaska down to Baja California. They tend to have coarser texture compared to Japanese uni, with similar sweetness. Losing to the over-populated Pacific purple sea urchin, this species has dramatically dropped in population in recent years, making them considerably less available for commercial use (Tabimori 2015, "What is Uni Sushi?").
Green Sea Urchin
Strongylocentrotus droebachiensis
The green sea urchin is found in the Arctic regions of the Pacific and Atlantic Oceans, primarily along the coasts of Canada, and Alaska and Maine in America. This urchin is well liked, known for being the only imported urchin on par with the local Bafun uni (Tabimori 2015, "What is Uni Sushi?").
Chilean Sea Urchin
Loxechinus albus
The Chilean sea urchin is considered top quality of Chilean urchin species, though is easily the cheapest uni found in Japan, often used at tourist-y conveyor belt restaurants (Tabimori 2015, "What is Uni Sushi?").
Sources
Sushipedia. (2022). "Uni Sushi". Arconia UG, https://www.sushi-pedia.com/en/sushi/uni/#Nishiki,%202022. Accessed 19 January 2024.
Tabimori. (2015). "What is Uni Sushi?". Sushi University, Tabimori Inc., https://sushiuniversity.jp/basicknowledge/what-is-uni.
Tabimori. (2015). "Sushi Visual Dictionary". Sushi University, Tabimori Inc., https://sushiuniversity.jp/visual-dictionary/?Name=Short-spined-sea-urchin-(Ezobafun-uni).
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