Red Dead Redemption 2 has 14 Legendary Fish Locations. Finding all legendary fish in RDR2 is needed for A Fisher of Fish Stranger Mission and they count as a collectible for 100% completion. They are also needed to complete the Fish Compendium under the Progress Menu. Only the first 13 legendary fishes are needed for 100%.

Legendary Fish are bigger and heavier versions of the normal fish and are harder to hook and catch. Along the way you'll automatically unlock the trophy "It was THIS Big!" for catching a fish weighing 16lbs (7.3kg).

First you should accept the Stranger Mission "A Fisher of Fish" given by Jeremy Gill. You must mail the fish to him via the post office. Bigger fish must be put on the back of your horse and brought back to the post office. Smaller fish go in your satchel automatically. In case you lose a big fish from your horse (or die after catching it) you can simply catch the fish again. Jeremy Gill gives you a map of 13 fish locations but it's not very accurate so we'll go through them in more detail on the in-game map.