Yellowtail is the rich, buttery, firm-fleshed fish of the Japanese amberjack, Seriola quinqueradiata — a fast, streamlined predator of the northwest Pacific whose pale rose flesh is prized above almost all others for sashimi and sushi. Clean and faintly sweet with a high, well-marbled fat content that melts on the tongue, it is the fish the Japanese call hamachi and buri, served raw in glistening slices or quickly seared, and central to the winter table.