[1] : The Collaborative International Dictionary of English v.0.48

yellowtail \yel"lowtail`\, n. zool.
   a any one of several species of marine carangoid fishes of
       the genus seriola; especially, the large california
       species seriola 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.
       1913 webster

   note: several other fishes are also locally called
         yellowtail.
         1913 webster
see also:
seriola seriola dorsalis cavasina white salmon sebastodes flavidus diplodus rhomboides 

[2] : WordNet (r) 2.0

seriola dorsalis
     n : game fish of southern california and mexico having a yellow
         tail fin syn: yellowtail
see also:
yellowtail 

Seriola >> S Words
Seriola, definition of term: Seriola
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