Spooning out fish: youngster comes first (7)
I believe the answer is:
ladling
'spooning out' is the definition.
(ladle is a type of spoon)
'fish youngster comes first' is the wordplay.
'fish' becomes 'ling' (ling is a kind of fish).
'youngster' becomes 'lad' (a young boy).
'comes first' means one lot of letters go next to another.
'ling' after 'lad' is 'LADLING'.
(Other definitions for ladling that I've seen before include "Serving liquid with a large spoon" , "Serving soup" .)