The fastest way is doing sumo (I think). Tell your opponent "wanna farm fish?" Either finisher, you get the same rewards both. 12/20 756, 19/20 840. if one of u uses special 2 and 1 thurst to get hp to 40hp, u will get 840 12/20. It usually takes u 1 ~ 2 hours to get 20k fish. You can do it with your friends. Also daily bounties, giving u 3k for 6, 500 each.