Fish-eating mammal (5)
I believe the answer is:
otter
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fish-eating mammal</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 otter that I've seen before include "Aquatic river mammal" , "one that eats fish" , "eg Tarka" , "fish-eater displayed" , "Something furry" .)