From Edo Culture: Daily Life and Diversions in Urban Japan, 1600–1868, by Nishiyama Matsunosuke, trans. and ed. by Gerald Groemer (U. Hawai‘i Press, 1997), pp. 170-171:
At the end of the Edo period the charming sight of sushi vendors selling kohada-zushi (sushi topped with a small gizzard shad) could be seen in the streets of Edo. Nigiri-zushi—bite-sized sushi made by squeezing a small amount of rice in the hand—was an Edo specialty that appeared during the Bunsei Period (1818–1830). This sushi soon became all the rage. The most conspicuous nigiri-zushi vendors sold kohada-zushi. These hawkers covered their heads with a hand towel in Yoshiwara fashion; they wore narrow-striped kimono tucked up behind, short coats with broad stripes and black silk collars, sashes known as Hakata obi, cotton leggings with white socks, and sandals made of straw and linen. Such a unique outfit made kohada-zushi vendors quite striking in appearance. From the start of spring until early summer sushi peddlers sauntered through the streets and called out in a mellifluous voice, “Sushi! Hey! Kohada-zushi!” …
Nigiri-zushi was also sold by “Atakematsu” of Atakegura in Honjo; eventually this sushi came to be known simply as “Matsu’s sushi.” … Most were mere street stalls, but true restaurants existed as well. At any rate, sushi was highly popular. From Edo the sushi fashion spread to the Kamigata area. In the late 1820s a restaurant called “Matsu no sushi” appeared south of Ebisubashi in Osaka. This was the first Osaka outlet of Edo sushi: but before long this specialty was sold at shops throughout Osaka.
Kohada （小鰭） and shinko （新子） are young and younger stages of konoshiro ‘dotted gizzard shad’, Konosirus punctatus (Temminck & Schlegel, 1846), according to Japanese Wikipedia, but a species utterly missing from English Wikipedia, where gizzard shad is summarily redirected to American gizzard shad (Dorosoma cepedianum), in a genus limited to eastern North America. The other five genera of the subfamily Dorosomatinae (gizzard shads) are not covered at all. The systematics of shads appear to be extremely complex.
I first heard of shad from my youngest uncle, who had a cabin down by the James River near the site of Virginia’s peculiar political gathering, the Shad Planking.