Grown-up elvers (4)
I believe the answer is:
eels
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">grown-up elvers</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for eels that I've seen before include "(Slippery) fish" , "Food for Cockney" , "Slithery fish" , "Feels small imprisoning water creatures" , "Slippery creatures" .)