New store stocks variable seafood (6)
I believe the answer is:
oyster
'seafood' is the definition.
(oyster is a type of seafood)
'new store stocks variable' is the wordplay.
'new' indicates anagramming the letters.
'stocks' indicates putting letters inside (stocks can mean carries or contains).
'variable' becomes 'y' (algebra).
'store' is an anagram of 'oster'.
'oster' going around 'y' is 'OYSTER'.
(Other definitions for oyster that I've seen before include "Pearl-yielding shellfish" , "Pearl producer" , "Proverbially reticent shellfish" , "Capital card" , "Tasty bivalve, may carry pearl" .)