You’ll notice on the topside of the fish is a slightly dark shadow and this is Nikiri and it was commonly used during the Edo period. Typically made using a mixture of shoyu, mirin, sake to help pave the way for the client instead of using a bath of shoyu. Unfortunately most foreigners have bad habits when it comes to sushi etiquette. They used shoyu without any understanding. Shoyu is the equivalent to salt and should be used sparingly, if at all. Nikiri has a umami balance to enhance the flavors is recommended.