Preheat oven to 425 degrees F (220 degrees C). Line a baking sheet with parchment paper or aluminum foil.
Discard skin, bones, and any crust from trout and flake fish with a fork. Combine flaked fish with soft bread crumbs, onion, mayonnaise, sour cream, lemon juice, Worcestershire sauce, salt, garlic powder, and black pepper in a bowl. Form mixture into balls and roll each ball in the panko. Arrange balls on the prepared baking sheet.
Bake in the preheated oven until croquettes are lightly browned and crispy, 15 to 20 minutes.
