Fish a theologian steeped in wine (7)
I believe the answer is:
haddock
'fish' is the definition.
(I know that haddock is a type of fish)
'a theologian steeped in wine' is the wordplay.
'theologian' becomes 'DD' (Doctor of Divinity degree).
'steeped in' is an insertion indicator (I've seen this in other clues).
'wine' becomes 'hock' (type of wine).
'a'+'dd'='add'
'add' inserted into 'hock' is 'HADDOCK'.
(Other definitions for haddock that I've seen before include "Swimmer" , "ish" , "Fish, often smoked" , "Fish like cod but smaller" , "Fish similar to but smaller than cod" .)