Where to find Wishiwashi in Sun, Moon, Ultra Sun & Ultra Moon

Super Rod: Route 13 (40%), Route 14 (40%), Route 15 (40%) + 10 more
SOS Encounter: Akala Outskirts, Route 13, Route 14 + 8 more
Surf: Route 14 (30%), Route 15 (30%), Brooklet Hill (30%) + 7 more
+ 2 more ways

Wishiwashi also appears in

How to get Wishiwashi in Sun, Moon, Ultra Sun & Ultra Moon

Its base catch rate is 60 out of 255 (higher is easier); the catch rate calculator works out your odds with each ball. For the look, the best colour match is Dive Ball.

Wishiwashi in every game · Pokémon Sun, Moon, Ultra Sun & Ultra Moon interactive map (Alola)