Doctor has time to fish (8)
I believe the answer is:
sturgeon
'to fish' is the definition.
(type of fish)
'doctor has time' is the wordplay.
'doctor' becomes 'surgeon' (surgeon is a kind of doctor).
'has' means one lot of letters goes inside another.
'time' becomes 't' (abbreviation).
'surgeon' going around 't' is 'STURGEON'.
(Other definitions for sturgeon that I've seen before include "supplier of delicacy" , "Our gents caught a large fish" , "swimmer" , "The fish for caviars" , "Fish sought for caviar" .)