Splatoon had five stages available at launch. The Wii U game released in May 2015 with five online Turf War arenas: Urchin Underpass, Saltspray Rig, Walleye Warehouse, Blackbelly Skatepark, and Arowana Mall.
That small starting lineup was intentional. Nintendo rotated the available stages rather than letting players freely choose from a large map list, helping keep matchmaking quick and making each arena feel familiar. Additional stages arrived through free updates, including Port Mackerel shortly after release.
The number can be confused with Splatoon's eventual total. The original game ultimately grew to 16 multiplayer stages, so five refers specifically to the launch-day selection, not the complete post-release roster. It also refers to multiplayer stages, not the separate single-player levels in Octo Valley.