This will take a while to obtain but there is a way to speed up the process in the long run. When you receive the daily fishing task (Assuming you have obtained the fisherman from the sea which is found either side of the world), it is best if you stockpile the quest fish. You can only have one quest fish in your inventory so all you need to do is put the quest fish you collect in a chest. You can now fish as many as you like, there are quite a few different quest fish so if you stockpile them, as I said this will be beneficial in the long run as you can easily just pick the fish from the quest each day and hand it in.
200 quest fish and it will unlock. It is a pain but manageable, hope this helped.