School of fish (5)
I believe the answer is:
shoal
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">school of fish</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for shoal that I've seen before include "School of fish" , "shallow water" , "Swarm of fish" , "Collection of fish" , "Lots of fish" .)