Large white sturgeon (6)
I believe the answer is:
beluga
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">large white sturgeon</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for beluga that I've seen before include "'Russian sturgeon, source of caviar (6)'" , "Small white whale; type of caviar" , "fish" , "Large Russian sturgeon" , "Large sturgeon or it's caviare" .)