Prepare cake mix according to package directions for baking one 9 x 13-inch cake using pound-cake variation (add instant pudding and an extra egg). Cool completely.
Using the fish template as a rough guide, cut fish shape from cake.
Tint vanilla frosting orange. Frost entire cake. Place gumdrop on cake for eye. Cut Twizzler to fit cake, and place on top to divide face and body. Trim Twizzler string into strips for tail. Using the back of a spoon, pull frosting away from cake to give body of fish a scaly look.