If you're out of ketchup, you could substitute tomato sauce for ketchup in this recipe.
Old recipe from 1957 Heinz advertising
Heat oven to 375˚F. Place 1 1/2 lbs. fish fillets in greased shallow pan. Brown 2 tbsp. chopped onion in 1 tbsp. shortening. Add 3/4 cup Heinz Ketchup, 1/4 cup Heinz Vinegar, 1 tbsp. Heinz Worcestershire Sauce, 2 tbsp. brown sugar, 1/2 tsp. salt. Simmer 5 minutes. Pour over fish. Bake 30 minutes or until fish is tender. Makes 5 to 6 servings.
Here's a vintage paint-by-number to inspire you to try the above recipe.