Food from the States transported by boat, mainly (5)
I believe the answer is:
sushi
'food' is the definition.
(I know that sushi is a type of dish)
'states transported by boat mainly' is the wordplay.
'states' becomes 'US' (abbreviation for the United States).
'transported by' is an insertion indicator (some letters carried or transported by others).
'boat mainly' becomes 'shi' (I can't justify this - if you can you should believe this answer much more).
'us' inserted into 'shi' is 'SUSHI'.
'from the' acts as a link.
Can you help me to learn more?
(Other definitions for sushi that I've seen before include "Raw fish dishes" , "put away in Japan" , "Oriental food" , "Exotic food" , "Japanese rice-based dish" .)