Fish in a fruitcake brought over (4)
I believe the answer is:
tuna
'fish' is the definition.
(tuna is a type of fish)
'a fruitcake brought over' is the wordplay.
'fruitcake' becomes 'nut' (I've seen this before).
'brought over' is a reversal indicator.
'a'+'nut'='anut'
'anut' back-to-front is 'TUNA'.
'in' acts as a link.
(Other definitions for tuna that I've seen before include "Large fish for the strange aunt" , "Tinned food fish" , "Large sea-fish" , "Species of fish" , "Large edible sea fish, often canned" .)