fish roe
The eggs of fish, usually lightly salted: depending on the species, small crisp grains or large, bursting pearls with a salty, briny taste.
Salted salmon, trout or lumpfish roe is sold in jars in the chilled section of most supermarkets, while finer kinds such as vendace roe or fresh cod roe are more likely found at a fishmonger, in Scandinavian shops or by mail order. The types can stand in for one another, though grain size, saltiness and colour will change, and dyed lumpfish roe can bleed onto pale dishes.
Substitute:
One roe can replace another, for example vendace roe with trout or lumpfish roe; the dish becomes coarser or saltier but still holds together. There is no convincing plant-based substitute for the taste and the burst of the grains.