Fish supplement found in wine from Germany (7)
I believe the answer is:
haddock
'fish' is the definition.
(haddock is a kind of fish)
'supplement found in wine from germany' is the wordplay.
'supplement' becomes 'add' (I've seen this before).
'found in' indicates putting letters inside.
'wine from germany' becomes 'hock' (type of German wine).
'add' going within 'hock' is 'HADDOCK'.
(Other definitions for haddock that I've seen before include "Edible fish like small cod" , "ish" , "Fish, often smoked" , "White fish" , "N. Atlantic food fish" .)