This stage has no golden crown enabled, all you need is to have a type of ocean species
Dolphin, Fish, Shrimp, Starfish, Sponge.
Scribblenauts Remix 2-4 Cheats Hints gallery:
2-4-1-a: Maxwell is building an aquarium! Fill the tank with five different types of animals.
2-4-1-b: Maxwell can put sea birds in the aquarium, as well as some mammals.
2-4-1-c: Sea cucumbers are animals too, despite the name.