Trout gets stewed by trainer (5)
I believe the answer is:
tutor
'trainer' is the definition.
(I've seen this before)
'trout gets stewed' is the wordplay.
'gets stewed' indicates anagramming the letters.
'trout' is an anagram of 'TUTOR'.
'by' is the link.
(Other definitions for tutor that I've seen before include "School" , "Private instructor" , "Coach, teacher" , "Give individual instruction" , "Personal coach" .)