Rinse the shrimp and crayfish tails and pat dry with a paper towel.
Chop about half of the shrimp and crayfish tails into smaller bits. Set aside a handful of shrimp for garnish, if you wish.
Chop the dill and chives and mix together with the shrimp and crayfish in a large bowl. Add the zest of about half a lemon to the mixture.
In a separate bowl, whisk together the sour cream, mayonnaise, and about a tablespoon of lemon juice. Set aside the other half of the lemon for garnish.
Stir the dressing into the shrimp mixture. Add the fish roe and stir well.