Yellowtail
Japanese sea fish of the jack family, known as hamachi or buri, with firm, rich, pale flesh and a mild, buttery flavour.
Caution: For raw use, buy only fish sold explicitly for raw consumption that has been frozen as required to kill parasites.
Yellowtail (Seriola quinqueradiata) is a jack fish that is mostly farmed in Japan; young or farmed fish are usually called hamachi, mature ones buri. The flesh is pale pink to beige with a dark red streak along the centre, firm yet rich in fat, especially in winter. Raw it tastes mild, sweetish and buttery; cooked it stays juicy and turns more savoury without drying out. Outside Japan it is usually sold frozen in Asian grocers or in sashimi grade from fishmongers and by mail order; the related yellowtail kingfish (Seriola lalandi), farmed in Europe and somewhat leaner, is often sold under the same name.
Substitute:
The closest match is the related yellowtail kingfish, which is slightly leaner and less buttery. For raw dishes, sashimi-grade tuna or salmon will do, though tuna is leaner and salmon has a distinctly different flavour; for braised or pan-fried dishes, mackerel works but tastes stronger and fishier.