There is a fishing exploit which will cause lag for nearby players also it's a level up exploit for players using Pokemons with wide area attacks.
ScreenShot:
Suggestion:
You can make a small cooldown for users or make the fishing function to work on wait,
Example:
You fish and he will be unable to move for 5 seconds then pokemon randomly appears or not.
You can make it to have a 10 seconds cool down and if the user attempts to spam it by hotkey 5 times within the 10 seconds he gets and extension on usability, instead of 10 he will wait 20.