To blanch the haricots verts, add beans to boiling, salted water for 20 seconds. Remove beans from boiling water and add to ice water to preserve coloring and prevent further cooking.
In a mixing bowl, combine the red wine vinegar, horseradish, dill, red onion, sour cream, and yogurt. Season with salt and pepper, to taste, and set aside.
In separate bowl, fold together the celery, cucumbers, haricots verts, crayfish, and whitefish. Combine the dressing with the crayfish vegetable mixture. Fold in mixed greens, season, and serve.