What you're seeing is caused by the fact that Fish Tycoon is designed to give priority to any other application that's running, whether it's in foreground or background mode - even system processes. So the 'jerkiness' that you sometimes see is not a bug in the program, but a result of Fish Tycoon yielding priority to another application or process. It was an implementation decision that was made in order to keep Fish Tycoon from affecting system and other application performance, and to allow people to run FT as more or less a 'background' application (since its real-time design doesn't require constant attention to make progress in the game). You can improve the performance of Fish Tycoon by closing all other applications that don't need to be running.