Herring mostly and well know in Eastern and Northern parts of Europe. Delicious side dish can be pickled, fermented or eaten raw. In Poland is often being used as a chaser for a Vodka shot 🙂 uuh ?
Tends to be very salty, and has a strong, specific taste.
Get the packed herring , not jarred. Russian or Ethnic stores should have supply of this fish.
It’s an acquired taste.