Teacher - a silly old trout? (5)

I believe the answer is:

tutor

I'm a little stuck... Click here to teach me more about this clue!

'teacher' is the definition.
(I know that tutor is a type of teacher)

'a silly old trout?' is the wordplay.
'trout' anagrams to 'TUTOR'.
Though, I'm not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for tutor that I've seen before include "Master" , "Personal coach" , "School" , "Trout (anag)" , "Individual teacher" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.