Let's start with where the confusion came from. The Polish word "''śledź''" (pronounced ''shletch'') is the imperative form of the verb "''śledzić''", meaning "to follow" or "to investigate". But it's also got another meaning, which would be more fitting in this context: "herring". So a better translation of "''śledź po japońsku''" would have been "Japanese-style herring". Now what the heck is that?
The Japanese-style herring has probably about as much to do with Japan as Hawaiian pizza has to do with Hawaii. In fact, it's a very appetizing appetizer that was quite popular in Communist Poland. The recipe largely boils down to wrapping a marinated herring fillet around a hard-boiled egg. Perhaps the idea of wrapping a piece of uncooked fish around something reminded someone of ''maki sushi'', giving rise to the Japanese association?
The egg and the fish are typically arranged on a bed of canned green peas laced with mayo and decorated with slices of onions and pickles. The combination of fishy, salty, sour and fatty flavours means that this simple ''hors d'œuvre'' pairs perfectly with a shot of cold neat vodka.