Trout cooked by instructor (5)
I believe the answer is:
tutor
'instructor' is the definition.
(I know that tutor is a type of instructor)
'trout cooked' is the wordplay.
'cooked' indicates anagramming the letters (letters cooked into a new form).
'trout' with letters rearranged gives 'TUTOR'.
'by' is the link.
(Other definitions for tutor that I've seen before include "trainer" , "college teacher" , "Private or university teacher" , "Trout (anag)" , "Personal coach" .)