Breed fish, we hear (5)
I believe the answer is:
raise
'breed' is the definition.
(I've seen this before)
'fish we hear' is the wordplay.
'fish' becomes 'rays' (I've seen this before).
'we hear' indicates a 'sounds like' (homophone) clue.
'rays' is a homophone of 'RAISE'.
(Other definitions for raise that I've seen before include "Breed" , "Lift - increase" , "climb" , "Uplift" , "Erect; grow" .)