American aboard vessel's reduced fare from Japan (5)
I believe the answer is:
sushi
'fare from japan' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
(Other definitions for sushi that I've seen before include "fare from Japan" , "Japanese cuisine" , "Rice, seafood cuisine" , "Japanese vinegared rice dish" , "Cold rice dish, often with raw fish" .)