From PowerPYX: “Tales of Arise has 44 Fish and 12 Fishing Locations. Catching all 44 types of Fish unlocks the Godly Angler trophy or achievement.
You unlock the ability to fish automatically from story progress in the area Talka Pond Road (3rd Realm: Menancia). This is about halfway through the story, after Dohalim joins your party as a playable character. In the same location where the story teaches you how to fish, you will also find the Fishing Expert. He gives you new lures after catching enough new fish types. After catching all types of fish you need to talk to him again to unlock the trophy / achievement. You can keep track of which fish you caught and which ones you are missing under Menu > Field Guide > Fishing Notes.”
Source: N4G PC Tales of Arise All Fish Locations Guide