To prepare the tuna, start by cutting the jugular to bleed the tuna out. Cut right at the top of the gill plate and cut up toward the eyes. Do this on both sides of the tuna. Then, cut a circle around the anus to free up the guts. Go back to the gill plate and cut the membrane in the gut cavity on both sides and, with one swift pull, the head and guts come out of the tuna. Then, you will pack the core very tightly with ice to keep the core cool. It is now ready to go on the table for sushi.