Fish is given to friend in a perfect world (7)
I believe the answer is:
ideally
'in a perfect world' is the definition.
(I've seen this before)
'fish is given to friend' is the wordplay.
'fish' becomes 'ide' (I've seen this before**).
'is given to' means one lot of letters go next to another.
'friend' becomes 'ally' (I've seen this before).
'ide'+'ally'='IDEALLY'
(Other definitions for ideally that I've seen before include "in theory" , "for preference" , "In perfect circumstances" , "In a perfect world, the best possible situation" , "In the perfect case" .)