The "tsuyu" rainy season spells the arrival of "maiwashi" sardines at the peak of their fatty lusciousness at the Choshi fishing port in Chiba Prefecture.

The fish are in season from mid-June through mid-July, and go by the local name of "nyubai iwashi" (start of tsuyu sardine).

The term can be traced back to a late Edo Period (1603-1867) document, according to the city's fisheries department.

"Around here, everybody knows nyubai iwashi," said Masayo Hasegawa, 61, who runs an eatery with her husband in front of Choshi Station. "When you peel the thin skin off the fish's back, you see a layer of white fat that's about 3 millimeters thick. Its melt-in-your-mouth sweetness is absolutely heavenly."

To promote the treasured local treat, Hasegawa formed "Choshi Umemon Kenkyukai" (group to study Choshi's delicacies). The group started organizing an annual event called "Nyubai Iwashi Matsuri" four years ago that is held from June through July.

It invites the public to savor sardines as sashimi and tempura, "zuke don" (rice bowl topped with soy marinated sardines) and "tsumire jiru" (soup with balls of minced sardines).

With six local restaurants participating, the event attracted about 1,000 visitors in the first year, and double that number last year.

According to "Dai-sendo no Choshi Iwashi Banashi" (Great boatman's tales of sardines), a book on the history of sardine fishing by Ron Shobo, the industry took off in the early Edo Period.

The book mentions the legendary bumper hauls in the early Showa Era (1926-1989), when fishermen lamented the glut and "massive schools of sardines made it appear that people could walk on water."

The fish's exquisite taste comes from the nutrient-rich waters off Choshi. The Oyashio and Kuroshio currents converge there, creating a perfect fishing ground.

Some 1,600 fishing vessels crowd the Choshi port, which leads the nation in fishery hauls. The port's immediate vicinity is packed with rows of eateries and drinking establishments.

Sardine catches started declining all over Japan in the early Heisei Era (1989-2019). Even Choshi's level today is less than one-fifth of its peak years.

Still, the port bustled with people when I visited, and the train station was festooned with banners proclaiming the coming festival.

The town of sardines is vibrant even in this dreary rainy season.

--The Asahi Shimbun, June 12

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Vox Populi, Vox Dei is a popular daily column that takes up a wide range of topics, including culture, arts and social trends and developments. Written by veteran Asahi Shimbun writers, the column provides useful perspectives on and insights into contemporary Japan and its culture.