Maybe vet fish hauled up (3)
I believe the answer is:
doc
'maybe vet' is the definition.
'fish hauled up' is the wordplay.
'fish' becomes 'cod' (cod is a kind of fish).
'hauled up' shows that the letters should be reversed in order.
'cod' back-to-front is 'DOC'.
(Other definitions for doc that I've seen before include "Medic (colloq.)" , "GP (colloq.)" , "Physician (colloq.)" , "Fox perhaps" , "Disney dwarf" .)