Use your Yo-kai Watch Lens on this object to discover Walkappa. This Yo-kai will ask you (sort of) to catch him some fish in the nearby riverbank. He will give you the fishing rod to do so.

Here in North America, it was only just recently revealed that we'll be receiving not one, but two versions of the sequel to Yo-kai Watch through Yo-kai Watch 2: Bony Spirits & Fleshy Souls.