Steam guide: https://steamcommunity.com/sharedfiles/filedetails/?id=2388853118

Download and Install

1. Download the map and save zip file to your computer
2. Extract downloaded file
3. Put file (FISHING_QUESTS.wld) in this folder:
C:\Users\%USERNAME%\My Documents\My Games\Terraria\Worlds
4. Put folder (Players) in this folder:
C:\Users\%USERNAME%\My Documents\My Games\Terraria
or create 40 characters in the game

In the game

1. Take first character
2. Enable autopause
3. Go speak to the angler
4. Loot every fish, that you need
5. Move every fish to the chest nearby the angler
6. Take one of the fish and deliver it
7. Repeat step 6 with another 39 characters
8. Go to sleep a repeat the whole process in the morning (4:30)
9. Enjoy your achievement

After completing the achievement

Delete map and characters in the game
OR
go to C:\Users\%USERNAME%\My Documents\My Games\Terraria\Worlds
and delete FISHING_QUESTS files
go to C:\Users\%USERNAME%\My Documents\My Games\Terraria\Players
and delete all 01 - 40 player files and folders

Fishing quests