Ultra-sun: Even fast-swimming fish Pokémon can be disabled by Golduck. It brings them to a standstill and seizes them.Moon: It swims along the banks of lakes and catches fish Pokémon. It takes them to the shore and quietly eats them up.Alpha-sapphire: Golduck is the fastest swimmer among all Pokémon. It swims effortlessly, even in a rough, stormy sea. It sometimes rescues people from wrecked ships floundering in high seas.
Prof. Lotus' Notes: Despite the Gold- prefix in it's name, this Pokemon is blue. I think this is a nod to how confused this Pokemon is and it's poor memory allows it to remember that it was once Gold colour but in it's confusion, forgot it evolved. You heard it here first.