Fish that may be jellied (4)
I believe the answer is:
eels
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fish that may be jellied</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 eels that I've seen before include "Conger --; jellied --" , "Slippery types" , "Slithery fish" , "Else they're fish" , "Feels small imprisoning water creatures" .)