Small herring (5)
I believe the answer is:
sprat
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">small herring</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 sprat that I've seen before include "Small edible fish" , "Small sea fish" , "Parts of a very small fish" , "Parts (anag.)" , "Small fish (used to catch mackerel?)" .)