Tsukudani are made of sea foods that are boiled in soy sauce and originated in the Tsukuda (in Chuo Ward Tokyo) area of Tokyo.
When Ieyasu TOKUGAWA visited Tsukuda Village in Osaka (present day Nishiyodogawa Ward in Osaka City), he took a liking to the boiled preserved foods made by local fishermen. It is said that Ieyasu organized the fishermen to move en mass to present day Tokyo/Tsukudajima Island and commanded them to produce 'Tsukudani' (seafood preserved by boiling in seafood).
In general the following boiled in sweetened soy sauce are called Tsukudani: seafood, in particular small fish, clams and other shellfish, seaweed such as kelp etc. and in mountainous areas insects such as locusts etc. (Also, the Tsukudani seen these days that is prepared by boiling ingredients in sweetened soy sauce is said to have been first produced at Asakusabashi in Tokyo by Funasa Co. Ltd). Beef tsukudani is also available. It is thought to taste best when eaten with cooked white rice.
Originally it was thought that when fish were considered too small for market the fishermen prepared them as preserved foods for use in their own homes. Being seasoned heavily, they stored well. Awareness of Tsukudani spread when samurai with alternative residences in Edo took Tsukudani back home as presents. Today, Tsukudani appears as local delicacies throughout the country in various locations and can no longer be considered as something solely from the Tokyo area.
As mentioned above, with roots as a foodstuff derived from a by product, something left over has turned into something that is saved and is even used to express something worthwhile or 'good enough to be turned into Tsukudani.'
Tsukudani sold these days in the market is light flavored and sweet. It also comes in vacuum packs and there are even varieties with no additives that require refrigeration.
In the days when refrigerators and shrink packs did not exist, quintessential Tokyo style sweet Tsukudani was used with confidence, much appreciated, and not affected even in summer when used at room temperature in rice balls and "bento" lunch boxes. These days at a few establishments such as "Funasa Co. Ltd. of Asakusabashi" and "Yanagibashi Komatsuya," etc., the authentic hand made Tsukudani produced by skilled artisans is testament to the heritage of Japanese cuisine that has been handed on to this day.
Lamprey eel (dried)