Creamy Smoked Trout with Apple and Horseradish on Crisp Brown Bread

Name: Creamy Smoked Trout with Apple and Horseradish on Crisp Brown Bread
Ingredients: 11 ounces smoked trout (about 3 fillets), coarsely flaked; 1 medium Granny Smith apple, peeled, cored, cut into matchstick-size strips; 1 cup finely chopped celery (about 2 stalks); 1/4 cup finely chopped fresh chives; 1/2 cup sour cream; 1/2 cup mayonnaise; 1 1/2 tablespoons fresh lemon juice; 1 tablespoon (or more) finely grated peeled fresh horseradish or prepared horseradish sauce; 1 loaf thinly sliced brown bread (such as Westphalian-style pumpernickel), lightly toasted, cut into triangles