(ie. Hirame aka Fluke. Not the case for Toro or other fatty fish)
Fish, like any other animal go through rigor after death.
It is at this stage in (white fish) Sashimi preparation that is most desirable by gourmands.
The filet should be sliced thinly by the skilled chef and enjoyed immediately.
I have had the pleasure of dining on a snapper sashimi style 20 minutes after it was caught.
It was a life changing experience.
Above:Sashimi platter served at Lan. Quite good. Professional refridgeration is the key to keeping these fish so fresh.
(Starting at 12 o'clock going clockwise)
Kanpachi - "Kori Kori"
Akami
Toro
Hamachi