Remove skin and bones from fish, cut fish into 2.5 cm (1 in.) pieces.
Place fish into bowl, add lemon juice, salt and enough vinegar to cover fish; mix well.
Cover bowl, refrigerate overnight.
Next day, drain fish well.
Place mayonnaise, lemon rind and sour cream in bowl, add fish, mix well.
Season with salt and pepper.
Place into large serving dish. Place separate bowls around fish containing chopped cucumber, peeled and chopped tomatoes, chopped shallots, peeled and sliced onions, chopped egg-white with sieved egg-yolk on top, and sliced beetroot.
Guests help themselves to fish, them a selection of the accomaniments.