Spiny-finned fish (4)
I believe the answer is:
bass
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">spiny-finned fish</span>' is the definition.<br/ ><span class="explanation-format__explanation">(bass is a kind of spiny-finned fish)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for bass that I've seen before include "Fish; male singing voice" , "Large percussion instrument" , "Fish (which sings?)" , "Low-pitched; a fish" , "bottom of sound?" .)