Oily food fish (8)
I believe the answer is:
mackerel
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">oily food fish</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for mackerel that I've seen before include "Banded food fish" , "Marine food fish" , "Edible fish" , "A food fish; type of sky" , "Fish caught by spinner (or sprat?)" .)