Bones of fish from the south (3)
I believe the answer is:
doc
'bones' is the definition.
(I've seen this before)
'fish from the south' is the wordplay.
'fish' becomes 'cod' (type of fish).
'from the south' is a reversal indicator (in a down clue, letters go up).
'cod' backwards is 'DOC'.
'of' is the link.
(Other definitions for doc that I've seen before include "Fox perhaps" , "Main dish" , "Medic (colloq.)" , "Quack" , "Consultant" .)