Unagi is freshwater eel which is a commonly used ingredient in Japanese cuisine, and is one of the most important kind of edible fish in Japan. In the later 20th century, the cultivating technique was established, yet wild unagi caught by fishermen is still preferred.
There are traditional ways of catching them. For example, piling rocks in the area where unagi live, and to catch unagi when they hide in the rocks. When unagi is caught, the smell of the water and bait is still strong, so to prepare for cooking, regardless of cultivated or wild, it will be put in pure water to remove the smell.
The most popular way to eat unagi is to cook as kabayaki, which is a type of teriyaki. The long body will be cut opened, and the bones will be removed. The meat will be spit-roasted, and will be soaked in a thick sauce made of soy sauce, rice wine, sugar, and sake, and will be roasted again.
Unadon and unajyu are the most popular unagi cuisines using kabayaki. When kabayaki is put on a bowl of rice, it is called unadon, “una” coming from the word unagi, and “don” coming from the word “donburi,” which means bowl of rice. When kabayaki is put on a box filled with rice, it is called unajyu. The word “jyu” coming from “jyubako,” a box shaped lacquer ware.
There is a tradition of eating unagi in summer since the Edo period (1603-1867). There was an unagi speciality restaurant which did not have much business in summer, but a person called Hiraga Gennai recommended to put up a poster saying “today is the day to eat unagi,” and the business thrived. Other unagi restaurants imitated to put up posters, and eating unagi in summer became popular.