Things You'll Need
Fresh ahi tuna, fillet or whole
Ahi tuna is a popular fish in Hawaiian and Japanese cuisines. For sushi, the tuna is served raw and sliced to fit the top of rice or served as sashimi. Since ahi is usually served raw, only the freshest fillet should be used in the preparation process. The fish must be cleaned and cut into strips before proper sushi cutting can begin. When cutting your fish or buying a fresh fillet, be aware of how many white sinew lines divide the meat. The sinew hinders cutting and makes for worse pieces of sashimi, so only serve the leanest cuts.
Remove the scales of a whole tuna by scraping the sides with a fish scaler.
Cut off the head, using a fish hammer for extra pressure if needed. Slice open the stomach from one side of the fish and remove all internal organs.
Cut through the stomach slice to the center bone of the fish. Repeat on all four sides of the fish quartering the fish into fillets. Cut to the belly bone in the center of the fish near the tail to separate the fillets from the tail.
Rinse the fillets thoroughly in cold water to wash away excess organ pieces. Remove all extra bones in the fillets with tweezers.
Arrange the fillets on a cutting board and trim the meat with a slicing knife. Slice off the thinner edges of the fillets, leaving the thicker parts on the table.
Slice the thick parts of the fillets into blocks about 1 1/4 inches thick, 3 1/2 inches wide, and 4 inches long. Arrange so the grain is running lengthwise in the fish.
Slice the fillet against the grain of the fish at a 25 degree angle. into 1/8 to 1/4 inch thick pieces with a sharp slicing knife. Do not saw at the fish with the knife. Instead, put pressure on the fish and drag your knife in one, long stroke.
When preparing or purchasing fillets, try to get slices that are about an inch thick. This helps make uniform slices when preparing nigiri.