A) Besides fishing, you'll want a way to kill something REALLY big, and its friends (see B & C). Item Identification is currently a dead skill (though it will be a support skill for the Imbueing skill being added for Stygian Abyss), so won't be needed on a fisher. A mage tamer (possibly with music and one or two bard skills) is a good choice for the Ancient SOS' net toss spawn - having firends are even better.
B) There are now 3 levels of normal SOS, and the Ancient SOS. When you open a Message in a Bottle, there is a 4% chance that it will be one of the white ASOS. It has a white chest when fished up (4000 gold, loot comparable to a level 4 or 5 treasure map), and a white net. Fishing up the chest is the easy and safe part.
The white net is similar to the green and colored nets, but brings up a Leviathan (White Kraken on Steroids) and at least a half-dozen OTHER creatures of the types nets normally bring up. As a result, there is a good chance you will die very quickly from the spawn in you aren't prepared (and sometimes when you ARE prepared). Suggest you NEVER throw a white net from a boat - use them only at Buc's den docks (where you can run as a ghost to the healer); the hard part is finding the sweet spots off the end of the dock that are still considered deep water for the toss.
When the Leviathan dies, everyone with looting rights get a chance at a minor artifact drop (you'll want to see the sections of Stratics and other pages discussing minor artifacts, as they came in about 5 years ago). If the person that tossed the net is a Grandmaster Fisher, they get a second check for an artifact drop if they don't get one from the looting rights drop. Two of the minor artifacts that only come from the Leviathan are the Seahorse statue and Ghost Ship Anchor, and those will sell for 5-20 million gold on most shards (much of the variability being from the different seahorse colors, and the fact that the Anchor seems to be one of the rarest drops in the game).
C) The ropes from the Kraken & Leviathan now have a crafting use (making and making the recharging element for a limited-use hitching post that functions as an in-house stable).
The Horned leather off sea serpents is still a valuable commodity, and while scale armor currently sucks, the Animal Trainer collection taker in the Britain Library community collection takes the scales at 20 points per (think of it as a modern version of Clean Up Britannia, but with stricter donation guidelines by craft). The fisher collection taker also takes fish and raw fish steaks, but takes forever to accumulate points. Note, though, that if you cut up a stack of fish, you get double the amount of fish steaks that number of fish normally would give cut up one at a time, minus 1 fish worth of steaks, so cutting up 80 fish 1 at a time would give 320 steaks, cutting a stack of 80 would give (320*2)-4=636 steaks (80 points one at a time, versus 159 points from the stack of the same number of fish).
A new crafting ingredient, white pearls, can also be fished up, and are reasonably valuable (20-50k each, depending on shard)
Treasure isn't much changed (other than using the AoS property system), but SOS tend to give better loot than T-Map chests in my experience (items with good combinations of high-value properties, I find more often in the normal (level 1-3) SOS, than in the same number of level 6 maps (another new addition, that have 1 minor artifact in each chest).
There's also an aquarium system you really don't have to be a fisher to do, using nets purchasable from NPCs, that give some interesting deco, rare fish and the like, but are a bit of a bother to maintain.
There are new woods and runic tools for carpentry, so there are now magical fishing poles created using them that can have skill bonuses, spell channeling (the ability to hold while casting), etc.
The list of what skill you have to be for each item is elsewhere in the forum, and I've been Grandmaster so long I can't remember the specifics.
Oh, and since they removed the anti-macro system, 8x8 skill training no longer works, but the caps on stat gains per day is gone, and many skills are easier to gain now, than before.
