Fish with scarlet fins (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fish with scarlet fins</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 opah that I've seen before include "Kingfish" , "Ocean swimmer" , "Large deep-sea fish" .)