Fishing Planet runs well in Linux excepting a few small glitches.
File locations:
/home/<username>/.config/unity3d/Fishing Planet LLC/FishingPlanet/ or ~/.config/unity3d/Fishing Planet LLC/FishingPlanet/
This directory contains the preference file (prefs) and the log file (Player.log), when sending a bug report to the developers this is where you find the log file they will ask for.
Graphical issues:
If you have a blank screen or a bunch of graphical garbage on startup try:
Right click on game in the steam library
Properties
Set Launch options
Type "./FishingPlanet.x86_64 -screen-fullscreen 0 %command%"
or
Edit the prefs file in the above directory to change;
<pref name="IsFullScreen" type="int">1</pref> to <pref name="IsFullScreen" type="int">0</pref>
Other than the graphical issue above the game has been stable for many hours of game play.