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.
Toast
Butter six slices of white bread (more if using sliced baguette) generously on both sides.
Fry in a frying pan on medium heat until both sides are golden.
Assembly
Scoop a generous portion of skagenröra onto each toast slice. Garnish with shrimp, a teaspoon of fish roe, a small slice of lemon, and fresh dill.