Sailor only gets shellfish (7)
I believe the answer is:
abalone
'shellfish' is the definition.
(abalone is a kind of shellfish)
'sailor only' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'only' becomes 'alone' ('alone' can be a synonym of 'only').
'ab'+'alone'='ABALONE'
'gets' acts as a link.
(Other definitions for abalone that I've seen before include "something to eat from the sea" , "produces an ear shell" , "Edible shellfish, sea-ear" , "Mother-of-pearl could have come from" , "sea mollusc" .)