Angel cake wrapper finally swallowed by fish (6)
I believe the answer is:
cherub
'angel' is the definition.
(I know that cherub is a type of angel)
'cake wrapper finally swallowed by fish' is the wordplay.
'finally' indicates one should take the final letters.
'swallowed by' indicates putting letters inside.
'fish' becomes 'chub' (chub is a kind of fish).
The last letters of 'cake wrapper' are 'er'.
'er' going within 'chub' is 'CHERUB'.
(Other definitions for cherub that I've seen before include "Sweet innocent baby" , "innocent young thing" , "Angelic infant" , "Angel portrayed as a winged child" , "A chubby infant with wings" .)