Source : Webster's Revised Unabridged Dictionary (1913)

Yellowtail \Yel"low*tail`\, n. (Zo["o]l.)
   (a) Any one of several species of marine carangoid fishes of
       the genus {Seriola}; especially, the large California
       species ({S. dorsalis}) which sometimes weighs thirty or
       forty pounds, and is highly esteemed as a food fish; --
       called also {cavasina}, and {white salmon}.
   (b) The mademoiselle, or silver perch.
   (c) The menhaden.
   (d) The runner, 12.
   (e) A California rockfish ({Sebastodes flavidus}).
   (f) The sailor's choice ({Diplodus rhomboides}).

   Note: Several other fishes are also locally called
         yellowtail.

Source : WordNet®

yellowtail
     n 1: superior food fish of the tropical Atlantic and Caribbean
          with broad yellow stripe along the sides and on the tail
          [syn: {yellowtail snapper}, {Ocyurus chrysurus}]
     2: game fish of southern California and Mexico having a yellow
        tail fin [syn: {Seriola dorsalis}]