Second pound needed for seafood (5)
I believe the answer is:
squid
'seafood' is the definition.
(squid is a kind of seafood)
'second pound needed' is the wordplay.
'second' becomes 's' (common abbreviation).
'pound' becomes 'quid' (UK slang for a pound).
'needed' is a charade indicator (letters next to each other).
's'+'quid'='SQUID'
'for' acts as a link.
(Other definitions for squid that I've seen before include "Edible eight-arm mollusc" , "Cephalopod mollusc" , "Tentacled marine creature" , "Ten-armed mollusc" , "Item of seafood" .)