Neither sour, nor fish, this is a local delicacy. Lamprey is in our area preferred smoked, and then fried in butter and stewed with cream. Best served with almond potatoes. The river lamprey is a fishlike jawless animal which lives in the sea and migrates up in the rivers in the autumn, where it is caught in traps in a traditional manner.
When Linneaus described lamprey fishery in early 18th century it was already an old custom. It was taxed by the crown at least as far back as the 16th century.