Fat fish (4)
I believe the answer is:
chub
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fat 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 chub that I've seen before include "Plump fish" , "Small river fish of the carp family" , "Fat relative of the carp" , "Fat freshwater fish" , "River fish; rhymes with public house" .)