Really simple achievement.
When you are fishing, you need to hook a fish, then lose it, 25 times.
This is much easier whilst Bass or Predator fishing, and you will get it naturally through the course of the game.
You can lose fish by having too much line tension, or letting them run free for too long. It's easier to lose a hooked fish if you 'poor strike' them on catch.
I'm currently not sure if having them bite, hook and break instantly whilst carp fishing counts for this.