Saba - Pastel drawing by Chef Kaz Matsune
(Originally posted on Quora.com)
Despite its current popularity, Maguro/Tuna was not widely consumed in Japan until the Edo period (1603-1868). The reasons were:
1. Unlucky to Eat
Tuna used to be called "Shibi" in Japanese. It had the same pronunciation as "day of the dead" and was considered unlucky to eat.
2. Japanese Preferred a Different Fish
Japanese preferred Tai/Read snapper over tuna because the word "Tai" rhymed with "celebration" (Meda•Tai).
3. Tuna is a large fish to transport
It is also said that tuna’s unpopularity was due to the physical size of the fish - Bluefin Tuna can be as long as 15 feet and weigh over 1,000 pounds. Because of the lack of refrigeration technology and transportation system, it was difficult to keep it fresh.
Starting around 1830, Edo/Tokyo had a large catch of tuna for many years and had an abundant supply of tuna, which lowered its price. Since tuna became so cheap, some sushi restaurants decided to try using tuna, which caught its popularity.
In the beginning, the way they served tuna was called "Zuke" - a soy-marinated tuna nigiri. By marinating in soy sauce, tuna lasted longer without refrigeration. It also brought a different flavor to tuna. Until then, tuna was either grilled or cooked and was considered not tasty.
Toro, tuna belly started to get popular around 1930. It is unclear exactly why it became so popular. One theory says it is due to the changing diet of modern Japanese, preferring more "fat" in their diet.