Tired of notice about fish having to be put back (6)
I believe the answer is:
sleepy
'tired' is the definition.
(falling asleep)
'notice about fish having to be put back' is the wordplay.
'notice' becomes 'spy' (spy can mean to notice or observe).
'about' is an insertion indicator.
'fish' becomes 'eel' (eel is a kind of fish).
'having to be put back' is a reversal indicator.
'eel' back-to-front is 'lee'.
'spy' going around 'lee' is 'SLEEPY'.
'of' acts as a link.
(Other definitions for sleepy that I've seen before include "One of the Seven Dwarfs" , "Ready for bed" , "Unwakeful" , "Likely to turn in" , "Lethargic" .)