The fish is サンマ/Sanma (English: Pacific saury, Swedish: Saira). It looks a bit like a mackerel and apparently belongs to that family. My colleague said it’s a typical autumn fish. It was a bit hard to filet it with chopsticks. But it was very tasty. The name of the dish was 新さんま定食; “new sanma fixed meal”. Price: 850 yen (6,45 euro/56 crowns).