Merriam-Webster Collegiate Dictionary - yellowtail

 noun  (plural ~ or ~s)  Date: 1709 any of various fishes having a yellow or yellowish tail: as  a. any of several carangid fishes (genus Seriola); especially a food and sport fish (S. lalandi) of the Pacific and Indian oceans having a yellow stripe along each side of the body  b. silver perch a  c. a snapper (Ocyurus chrysurus) that is a sport and food fish found from Massachusetts to Brazil and is olive to bluish above with yellow spots and a broad yellow stripe along each side of the body — called also ~ snapper