The fish commonly used for maguro sushi is tuna. In Japanese sushi terminology, maguro generally refers to tuna, especially the familiar lean red cuts served as nigiri or sashimi.
Tuna is prized because its firm flesh holds together well when sliced and has a clean, rich flavor. Several tuna species appear in sushi, including bluefin, bigeye, and yellowfin. The fatty belly portion of tuna is called toro, with the especially fatty cuts known as otoro and the moderately fatty cuts as chutoro.
Maguro is a broad category rather than the name of one single species. Menus may identify the fish more precisely as honmaguro, often translated as bluefin tuna, or specify akami for the lean red meat. The word tuna itself covers several related fish in the genus Thunnus.
Maguro should not be confused with sake, the Japanese sushi term for salmon, or hamachi, which usually means young yellowtail. Preparation also varies: tuna may be served raw, seared, marinated, or mixed into spicy tuna rolls.