It is probably cutting fish just before serving. For a big size fish, keep its skin on the meat during the process of preparing and cutting into half, and at every serving use sogigiri* as much as customers eat. Protected by the skin, the fish flesh will expose to air for the first time as it is cut. The skin blocks the oxidation process significantly because the fat in fish centers right under the skin in general. Needless to say, even with any amazing fish, it loses flavor if the fat gets oxidized.
＊Sogigiri－A method of cutting which makes a slice thinner with a greater surface, by holding the knife diagonally and cutting in line with the cutting board. Usually used for white fish with firm flesh because it is easier to be eaten when served thin.
Hirazukuri－A method of cutting which gives thickness to each slice so that the texture of sashimi can be enjoyable. This is used for akami like tuna.
We hope this information will be helpful.
Revision date: April 1, 2020