Bring up flatfish in conversation (5)
I believe the answer is:
raise
'bring up' is the definition.
(as in bringing up children)
'flatfish in conversation' is the wordplay.
'flatfish' becomes 'rays' (flatfish are a type of ray).
'in conversation' indicates a 'sounds like' (homophone) clue.
'rays' is a homophone of 'RAISE'.
(Other definitions for raise that I've seen before include "Bring up; levy" , "Collect - increase in pay" , "Call up" , "Pick up" , "Breed" .)