Cartilaginous fish (3)
I believe the answer is:
ray
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cartilaginous fish</span>' is the definition.<br/ ><span class="explanation-format__explanation">(ray is a kind of cartilaginous fish)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ray that I've seen before include "Beam of light or flat fish" , "Narrow beam of light" , "Man, maybe" , "Beam - skate" , "Second note for the flat fish" .)