After a lot of work and research, I've found a second way to level really fast. The first was of course fishing with full inventory, thus dramatically lowering your fatigue levels.
this second method can be rather expensive, but I've seen ridiculous fast skillups when done.
It's pretty simple, here's what you need:
*LOTS of inventory space. Like, TONS, 20-25 open slots at least.
*A couple stacks of your choice bait. Lures won't work with this trick, aside form minnows, which are kinda cheap from the guild.
*Quick access to an NPC that sells willow rods. I suggest Lusiane (F-8 San d'Oria South)
So here's how it works. The weaker a rod is, the higher chance of getting skillups. Thus rods like the ebisu and lu shang are actually really hard to skillup with, since they're so strong. This is true and has been proven.
On the other end, the willow rod, the weakest, actually increases the chances of skilling up pretty dramatically. The downside? The things so damn weak, I wouldn't be surprised if it snapped on a Pamtam Kelp....
So what do you do? Simple, use bait instead of lures. Pick the fish you want to skill on and buy 20 or so willow rods. Then equip one and your bait, and go to town.
A lv 80 fishing friend of mine, who happened to have the pelican ring, tried this out with both. He was extremely taken aback when he Got 3 .2 skillups in a row, then a .1, one no skillup, and then a .3 skillup.
He got an entire level in 6 catches. This is no trick, no joke, no spam. It works, and it works well. Downside is there ARE a few points when the only fish you can really level on require the use of a lure.
IE It's really hard to catch shall shells with anything but rogue and robber rigs. And not many people are willing to toss away 20K per catch, no matter how good the skillups are.
http://www.finalfishing.com/FishingRods.aspx?rid=11
As with the Yew, the extremely low durability of the Willow Rod limits its usefulness to all but a few specific target fish and locations. However, Willow Rods will actually come in handy if you decide to level up through the late 50s or 96-100 by breakfishing on the Ferry.