Fishing Fatigue?
K you have two different issues and one of them at least(fatigue) has many influencing factors. The simpler one is daily fishing cap, which lvl may affect, which is a flat maximum number of bites you get and after which you will only get the "you didn't catch anything" message.
The second is fatigue, which is a value which the higher it is the fewer bites you will get and the more of those bites will be low quality catches like items. The longer you are in a particular zone without leaving the more fatigue you will have. In towns fatigue accumulates much faster then when outdoors. Fatigue accumulates faster from cancelling a catch rather then just catching it and throwing it away if you do not want it. Fatigue is reset when you zone to a new area, so the best way to deal with it is to zone as soon as you start getting alot of item catches. Fatigue is also reset when the server resets at midnight JP time. Logging off does not reset your fatigue, not sre why but I would guess as an antibotting measure to force bots to either get crappy catches or result to very complicated coding for moving about.
The second is fatigue, which is a value which the higher it is the fewer bites you will get and the more of those bites will be low quality catches like items. The longer you are in a particular zone without leaving the more fatigue you will have. In towns fatigue accumulates much faster then when outdoors. Fatigue accumulates faster from cancelling a catch rather then just catching it and throwing it away if you do not want it. Fatigue is reset when you zone to a new area, so the best way to deal with it is to zone as soon as you start getting alot of item catches. Fatigue is also reset when the server resets at midnight JP time. Logging off does not reset your fatigue, not sre why but I would guess as an antibotting measure to force bots to either get crappy catches or result to very complicated coding for moving about.