A Fisher of Fish

 is a Stranger mission in Red Dead Redemption II. The quest becomes available during Chapter 3.

Story
Jeremy Gill, a self-proclaimed legendary fisherman, is found fishing off the doc after the Van der Linde gang moves to their new camp in Clemens Point. After he is approached, he asks if the player is interested in an autograph or photograph before leading them inside of his cabin to show off his livelihood - selling stuffed fishes. He gives the player a map of all Legendary Fish sites in the world and says he'll pay a handsome price for any that are sent his way.

Walkthrough
There are a total of 13 Legendary Fish that can be caught across the world.