I’m a blogger who live in Toyosu, Tokyo.
There are two ways to observe the Tuna auction in the early morning hours at TOYOSU FISH MARKET.
（I’m sorry if my writing is hard to read. My English is not good.）
A) the Tuna auction via observation deck on 3rd floor.
B) the Tuna auction via observation deck on the lower floor.
“A”, No application required. Just visit the market to see it. Observation time is 5:30AM to 6:30AM. No problem.
“B”, You need apply for the Tuna auction via observation deck on the lower floor.
You need to sign up by the 14th of the previous month, and must win from the drawing.
A maximum of 5 people can participate per application.
It is around 21st to announce the winners.
Winner are Observation time is 5:30AM to 6:30AM.
You will gather at the 3rd floor of the market management facility building at 5:30. You can watch 10 minutes out of 5:45 to 6:15.
— とよすと (@toyosu_tokyo) January 15, 2019
For example, you would like to visit Toyosu fish market on 25 March 2019. You need apply until 14 February.
You can apply by phone, but it is difficult if You can not speak Japanese.