Bring up boys initially wanting fish (5)
I believe the answer is:
roach
'fish' is the definition.
(roach is a kind of fish)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for roach that I've seen before include "creepy-crawly" , "Fresh-water food fish" , "member of family carp" , "Trim" , "bedbug in the Waldorf?" .)