Seafood years in store going off (6)
I believe the answer is:
oyster
'seafood' is the definition.
(oyster is a type of seafood)
'years in store going off' is the wordplay.
'years' becomes 'y' (abbreviation).
'in' indicates putting letters inside.
'going off' indicates anagramming the letters (letters go or move around).
'store' is an anagram of 'oster'.
'y' going within 'oster' is 'OYSTER'.
(Other definitions for oyster that I've seen before include "Pearl producer" , "Capital card" , "Mollusc sometimes eaten alive" , "Pearl-producing bivalve" , "Marine bivalve" .)