Male (and half male) shellfish (6)
I believe the answer is:
cockle
'shellfish' is the definition.
(cockle is a kind of shellfish)
'male and half male' is the wordplay.
'male' becomes 'cock' (male chicken).
'and' says to put letters next to each other.
'half' indicates taking half.
'male' with half the letters taken is 'le'.
'cock'+'le'='COCKLE'
(Other definitions for cockle that I've seen before include "Mollusc - cornfield weed" , "Common edible bivalve" , "Edible bivalve mollusc" , "occupant of shell" , "Seafood item" .)