If the tuna is filleted in 4 parts; 2 backs and 2 belly sides, the bone remains. Fresh tuna bone is a treat from the top shelf. The backbone of a tuna is called Maguro-naka in Japanese and can reach a weight of up to 35 kg. Like many other fish, the bone can be a culinary enrichment. No matter how good or specialized the tuna fader is, there is always a residual of the fish meat on the back of the bone. The fish meat that remains is akami. Rapid processing of the bone is necessary to prevent discoloration of the meat. The best way to remove the meat is to remove it from the bone with a spoon.