Pickled herring (7)
I believe the answer is:
rollmop
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">pickled herring</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for rollmop that I've seen before include "Ex-swimmer preserved" , "Pickled fillet of raw herring" , "swimmer that's soused" , "savoury dish" , "Curled-up herring fillet" .)