Odd story about eastern shellfish (6)
I believe the answer is:
oyster
'shellfish' is the definition.
(oyster is a kind of shellfish)
'odd story about eastern' is the wordplay.
'odd' indicates an anagram.
'about' is an insertion indicator.
'eastern' becomes 'e'.
'story' anagrammed gives 'oystr'.
'oystr' placed around 'e' is 'OYSTER'.
(Other definitions for oyster that I've seen before include "Seafood item sometimes eaten alive" , "Mollusc sometimes eaten alive" , "A pearl may grow in it" , "Succulent shellfish" , "Source of pearl" .)