Soak the bread in a cup of water for five minutes, then squeeze out the excess moisture and set it aside.
In a blender or a food processor, process together the carp roe and shallot. Add the bread, 1/4 cup at a time, until smooth. Drizzle in the olive oil in one small and steady stream while the mixer is still running. Do the same with the lemon juice and blend until the mixture is smooth and fluffy.
Empty the taramasalata into a small bowl, cover, and keep refrigerated when not in use.