Loaf brought back with a fish (4)
I believe the answer is:
tuna
'fish' is the definition.
(tuna is a type of fish)
'loaf brought back with a' is the wordplay.
'loaf' becomes 'nut' (I've seen this in other clues).
'brought back' says the letters should be written backwards.
'with' says to put letters next to each other.
'nut' back-to-front is 'tun'.
'tun'+'a'='TUNA'
(Other definitions for tuna that I've seen before include "Large sea-fish" , "Popular food fish" , "swimmer" , "Large edible sea fish, often canned" , "Large salt water fish" .)