Funny story about Eastern shellfish (6)
I believe the answer is:
oyster
'shellfish' is the definition.
(I know that oyster is a type of shellfish)
'funny story about eastern' is the wordplay.
'funny' indicates an anagram.
'about' is an insertion indicator.
'eastern' becomes 'e'.
'story' is an anagram of 'oystr'.
'oystr' placed around 'e' is 'OYSTER'.
(Other definitions for oyster that I've seen before include "Edible bivalve mollusc" , "Pearl producer" , "Secretive individual" , "Shellfish - colour" , "Bivalve - may be pearl carrier" .)