Akami generally refers to red-colored meat like beef and fish meat.
At a sushi restaurant, the typical Akami fish are tuna and bonito. The meat gets its red color from the high hemoglobin and a colored protein called myoglobin, which is specific to migratory fish.
Colored proteins perform the function of carrying oxygen to the muscles. Since migratory fish swim at high speeds and are very active, they require oxygen. This is the reason why they contain a large amount of colored proteins and turn red. Also, they contain a higher amount of umami substances than white flesh fish, as well as a higher amount of fat, which is why red flesh fish tastes richer than white. However, it can smell fishier more easily, due to the oxidation of the fat and decomposition.
At a sushi restaurant, when you order Akami, you will be served tuna. The word Akami exists for tuna.There is a lot of Akami on the back side and has less fat content than toro. This part is rich in minerals like iron so you can enjoy the tuna’s natural umami.