Fish and a fruit served up (4)
I believe the answer is:
tuna
'fish' is the definition.
(tuna fish is a kind of fish)
'a fruit served up' is the wordplay.
'fruit' becomes 'nut' (nut is a kind of fruit).
'served up' shows that the letters should be reversed in order.
'a'+'nut'='anut'
'anut' in reverse letter order is 'TUNA'.
'and' acts as a link.
(Other definitions for tuna that I've seen before include "(Meat of) large fish" , "Popular food fish" , "Skipjack --, blue-fin --" , "Fish sold in cans" , "Large fish for the strange aunt" .)