Youngster consuming hot fish (4)
I believe the answer is:
chub
'fish' is the definition.
(chub is a kind of fish)
'youngster consuming hot' is the wordplay.
'youngster' becomes 'cub' (I've seen this in other clues).
'consuming' means one lot of letters goes inside another.
'hot' becomes 'h'.
'cub' placed around 'h' is 'CHUB'.
(Other definitions for chub that I've seen before include "Thick-bodied river fish" , "Plump fish" , "River fish; rhymes with public house" , "Thick-bodied European fish" , "Fat relative of the carp" .)