I just wanted to start off by saying that I really enjoyed this game at first and thought it was surprisingly fun. Then I started working on the 1000 fish achievement.
What a grind!!! The method I am using is to repeatedly abuse the fish of 10 Mile Gorge in Arcade mode. In a full play through of the tournament, I am averaging between 25-30 fish. The fish on 10 Mile Gorge are the easiest to catch and most time efficient. Hope this helps anyone that decides to 1K this game.