Place the cubed bread onto a baking sheet, and bake in the preheated oven until dry and golden brown, about 10 minutes. Remove and cool.
Meanwhile, mince the cod and shrimp and place into a mixing bowl along with the beaten egg whites. Sprinkle in the cornstarch, salt, pepper, and ginger. Mix well, and form into 8 balls. Roll the balls in the toasted bread cubes and set aside.
Heat oil in a deep-fryer or large saucepan to 350 degrees F (175 degrees C).
Fry the balls 4 at a time until they turn light, golden brown, about 2 minutes. Drain on a paper towel-lined plate. Once the second batch of croquettes has been fried, return the first batch to the hot oil, and fry again until deep, golden brown and the croquettes are no longer opaque in the center, drain on paper towels while frying the second batch.
