Arcanite Fishing Pole is the best fishing pole available for fishing, with a +40 bonus to fishing skill.
The Arcanite Fishing Pole has no explicit level requirement, however one must be level 10 to train in Artisan level fishing in order to reach fishing skill level 300 and equip the Arcanite Fishing Rod. You can acquire it earlier, but not equip it.
Even so, it is not necessary to acquire it. The most difficult areas to fish require only 575 fishing skill to have no fish get away. This can be accomplished with 450 fishing skill, a +20 fishing pole, a +100 fishing lure, and any other +5 fishing skill gear. The advantage of the Arcanite pole is that you can use +75 fishing lures with a little more fishing gear.
A previous patch increased the bonus from +35 to +40.
According to El's Extreme Anglin', the Arcanite Fishing Pole will be given a new icon and model in Cataclysm. Currently, only the wire frame and inventory picture are available.