Combine the flaked smoked whitefish, celery, red onion, dill, and parsley in a large mixing bowl.
In a separate small bowl, whisk together the mayonnaise, sour cream, Dijon mustard, lemon juice, and lemon zest until smooth and well combined.
Pour the dressing over the whitefish mixture and gently fold everything until the fish is evenly coated—season with salt and pepper to taste.
Cover and refrigerate the salad for at least 30 minutes to allow the flavors to meld.
Serve chilled, garnished with lemon wedges and additional fresh herbs if desired.