Recently i was fooling around on Molten-WoW 3.3.5 and i stumbled upon a bug that makes it extremely easy to level your fishing skill, so i decided to share it with you guys. You need to be a warrior to do this though. Switch to fury spec and pick up the Titan's Grip Talent, then equip a 2h weapon in your Main Hand slot and a Fishing Pole in your Off-Hand. Then go to the Level 80 Training Dummy and start attacking it. You will notice your fishing skill is increasing with each hit, as if it was a weapon skill :P
Here is a demonstration and proof that it works Molten-WoW Exploit: Level your Fishing Skill while Afk - YouTube
I hope you find that useful, have fun