Shun (旬) — Japanese Fish Seasonality.
Why the same fish tastes different in December than in July.

What is shun?

The kanji 旬 depicts ten days — the span of one third of a lunar month — and originally described the brief peak of a crop or catch before it passed. In Japanese culinary culture, shun expanded to mean the full season when an ingredient is at its best: richer, more flavorful, more alive than at any other point in the year.

For fish, shun is not about calendar dates. It’s about biology. A fish’s flavor changes dramatically across the year because its body is doing different things at different times — building fat for winter, burning it for reproduction, migrating through waters of different temperatures and nutrient densities. When you eat a fish in shun, you are tasting the outcome of that biological moment.

The concept is tied to two strands of Japanese aesthetic thought. Wabi-sabi finds beauty in impermanence: a seasonal fish is not perfect forever — it is perfect right now, and that fleetingness is part of what makes it worth attention. Mono no aware is a quiet awareness of passing time: a shun ingredient appears, reaches its peak, and fades. In its coming and going, we feel the season move.

Bluefin tuna: the winter fat peak

Pacific bluefin tuna (Thunnus orientalis) peak in December through January — a fact known to any serious sushi chef, but one whose mechanism is worth understanding.

Bluefin are mixed capital-income breeders, a term from reproductive biology. It means they finance the energy cost of spawning primarily from stored capital — fat accumulated in advance — rather than from food eaten during the spawning season itself. Specifically, they stockpile triacylglycerols (TAG) in the liver and white muscle throughout the year. When spring spawning begins, TAG levels in white muscle and liver drop sharply as the fat is transferred directly into developing oocytes (eggs).

Winter is the moment just before that transfer begins. Triacylglycerol in white muscle and liver is at its annual maximum. For otoro and chutoro, this means denser, more layered marbling. For akami (lean loin), even the lean red meat takes on a richer, more complex umami character — denser and more mineral than its summer counterpart. By late spring, the same fish tastes noticeably leaner.

Summer akami is not inferior — it has a brighter, more lifted acidity that suits lighter preparations and wasabi-forward nigiri. But if you want the fish at its most luxurious, December through January is the window.

Sashimi DC’s Goto Bluefin Tuna from Nagasaki arrives weekly year-round, so you can taste both the winter peak and the leaner summer expression.

Katsuo: the fish with three seasons

Katsuo (skipjack tuna, bonito) is the most seasonally expressive fish in Japanese cuisine. A single species; three completely different eating experiences across the year. Sashimi DC does not currently carry katsuo, but its story is the clearest illustration of what shun means.

Spring: hatsugatsuo (初鰹)

April through May. Katsuo migrate north along the warm Kuroshio Current from Kyushu up to Hokkaido in search of food. These are lean, actively swimming fish — firm flesh, clean acidity, brisk oceanic flavor. The appearance of hatsugatsuo in sushi restaurant neta cases has signaled the arrival of spring for centuries. Served as lightly seared tataki or raw, its brightness is the flavor of the season.

Autumn: modorigatsuo (戻り鰹)

September through October. Having spent the summer feeding in the nutrient-rich zone where the warm Kuroshio and cold Oyashio currents mix near Hokkaido, the fish have fattened substantially. As water temperatures cool in autumn, they migrate south again to spawn. These returning katsuo — modori means “to return” — carry a full season’s feeding in their flesh: buttery, deep umami, softer texture. A different fish in every way that matters at the table.

Winter: mayoi-gatsuo (“lost” bonito)

A rare and recent phenomenon. Some schools, instead of following the main southern migration route, stray into the colder Sea of Japan off Niigata and Toyama. The frigid winter water triggers the development of a thick subcutaneous fat layer unlike anything seen in spring or autumn fish. At the Toyosu Market in December 2019, this out-of-season curiosity fetched over ¥7,000 per kilogram at wholesale — rivaling high-grade Oma tuna. Luxury sushi restaurants in Tokyo now seek it out specifically.

Uni: staggered peaks across regions

Hokkaido uni does not have a single shun — it has staggered peaks by variety and harvest region, which is why good uni is available across most of the year if you know where to look.

The primary summer peak (June through August) is Ezo Bafun Uni from Rishiri, Rebun, and Shakotan — the outer northwest coast of Hokkaido. This is the window most associated with premium uni in Japan: deep orange-gold color, firm lobes, rich sweetness driven by high concentrations of glycine, alanine, glutamate, and AMP in the gonad. The biological driver is pre-spawning gonad development: the gonads are at maximum weight and richness just before spawning, which occurs in late summer. After spawning, they shrink and bitterness can increase.

Kita Murasaki Uni peaks in spring and autumn; Hakodate produces year-round including winter; late winter harvests come from Hidaka (Shizunai to Erimo on the Pacific coast). This regional staggering is why Sashimi DC can carry Hokkaido uni in most seasons — but availability varies week to week. Follow @keita_sashimi_dc or check the shop for current stock.

Full guide: Hokkaido Uni in Washington DC.

Scallops: two shun windows, two farming systems

Hokkaido scallops (Patinopecten yessoensis) have two genuine peak seasons because two different farming methods produce fundamentally different scallops.

Summer shun (May–September): Okhotsk Sea and Soya region, farmed by the jimaki (bottom-seeding) method. Juvenile scallops are released onto the cold seafloor and grown for several years in fast-moving, nutrient-rich water. The result is a firm, springy adductor muscle with a clean, mineral sweetness — ideal raw, where texture is everything.

Winter shun (December–March): Funka Bay and Notsuke Peninsula, farmed by the suika (suspended longline) method. Scallops hang on lines through the coldest months, metabolizing slowly in near-freezing water. The result is a richer, more concentrated umami — less about crunch, more about depth. These respond beautifully to a brief sear in butter or a light dashi.

April is spawning season for both systems. The adductor muscle depletes sharply — thinner, less sweet, less firm — which is why Sashimi DC does not carry scallops in that month.

Full guide: Hokkaido Scallops in Washington DC.

Unagi: the summer stamina tradition

Unagi (freshwater eel) is eaten in Japan on Doyo no Ushi no Hi — the day of the ox during the summer doyo period in the traditional lunar calendar, typically falling in late July. The custom dates to at least the Edo period. The reasoning: unagi is high in protein, B-vitamins, and fat that provides sustained energy — a practical choice for maintaining stamina through Japan’s notoriously hot and humid summers.

Today Doyo no Ushi no Hi is one of Japan’s highest-volume food consumption events. Sashimi DC’s Kagoshima Unagi Kabayaki from Daishin is available year-round as a frozen product.

Shun at Sashimi DC

Most of what Sashimi DC carries is shaped by shun. Goto Bluefin Tuna is richest December through January; weekly updates note when seasonal character shifts. Hokkaido Uni availability follows regional harvest calendars rather than a fixed schedule. Scallops go quiet in April. Hotaruika (firefly squid) from Toyama Bay is available only in March and April when the bioluminescent females come to shore to spawn — a two-month window, then gone for the year.

Fish arrive at Sashimi DC every Wednesday, ~48 hours from Miyazaki. Thursday and Friday are the best days to order — stock is fully replenished and the week’s seasonal arrivals are all available. Follow @keita_sashimi_dc for weekly cut announcements and seasonal notes.