One can learn from a trout when it's swimming (5)
I believe the answer is:
tutor
'swimming' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'one can learn from a trout when' is the wordplay.
'trout' anagrams to 'TUTOR'.
Though, I am not clear how the anagram is indicated.
'it's' is the link.
Can you help me to learn more?
(Other definitions for tutor that I've seen before include "Private instructor" , "Edify" , "Individual teacher" , "Private educator" , "Private or university teacher" .)