The itamae at my favorite sushi-ya went crazy on my chirashi bowl this week and tossed in a couple of new things. In addition to a whole soy-cooked baby octopus (yum!) he added a couple of slices of fish that were unlike anything I've had before.
There was intact silvery skin on one edge of each slice, but the meat was VERY yellow. And it was quite sweet, with a vinegar tang. There was an oily fish flavor, but the sweetness was about as prominent. Most interestingly, it was very firm - not quite crunchy, but close. Similar to the texture of frozen fish, even though it was not particularly cold.
Shige-san said that the fish was herring, and said that it had been marinated in sweet vinegar, but this was a lot more than ordinary marinated fish. He didn't elaborate further, and between the press of business and the language barrier I didn't get any more info.
That was three days ago and I'm still thinking about this stuff. Is it a traditional dish that anybody else is familiar with? I'd love to get more information (although I won't complain if I have to be satisfied with just finding more in my bowl again next week).