Bigeye or Yellowfin are two types of tuna commonly served at sushi bars. Ahi is the Hawaiian name for yellowfin tuna, and is also used to refer to both bigeye and yellowfin tuna. Bigeye tuna is a deep-water fish with a firm texture and a rich flavor, while yellowfin tuna is a lighter-fleshed fish with a milder flavor. Both types of tuna are popular in sushi dishes, and can be served raw, seared, or grilled.