A few days ago you were told about the Midas Fish. There is another legendary fish called the Vendatta Flopper. Once activated it will allow you to spot enemies in the vicinity, just like the cards the Acolytes had in season 3.
To catch it, you'll have to be patient, but not only...
You won't be able to get it with a simple fishing rod. It will have to be improved in a workbench (100 of wood, brick and iron) in order to promote it as a Pro Fishing Rod.
Once you have it in your possession, be patient and you may catch the precious fish. There are no specific areas, you should be able to catch it anywhere.
Original content by Maxime "Biaggi" Ricoveri.