As mentioned on the "Achievements" page here at El's Anglin, several (seventeen, to be exact) fishing-related achievements are so far planned for Wrath of the Lich King. Many are not yet finished but will be fleshed out as Beta unfolds.
I was fortunate enough to be invited to Beta recently and, like any good (obsessed) angler, one of my first acts was to try fishing. Sadly, there are no new "fishable" fish yet in the game. There is a "northern barb fish", which is the objective of a two-part quest where the first part involves literally banging on stuff that looks like seaweed until one of three things pops out: an undead spy, a crab, or the barbed fish. You then get pulled into combat with whatever popped out. It's reminiscent of the Terokkar "Taken in the Night" quest where you have to free people from spider cocoons. In other words, not very fun. It took me a while to do the two-part series and there wasn't even a fun item reward. It was just around 4 or 5 gold per stage.
As also indicated here on El's Anglin', there's also a Northern Salmon quest fish, but I haven't done that quest yet.
Going back to achievements, some of the most interesting achievements tie into Burning Crusade. There are two Mr. Pinchy achievements: one for getting his pet, the other for fishing him (or one of thirteen other rare fish). Oddly, the "Mr. Pinchy's Magical Crawdad Box" achievement does not automatically light up the "The Deadliest Catch" achievement, although you obviously need to catch Mr. Pinchy to get his box. I submitted a "bug" suggestion regarding this.
There is also an achievement relating to the Old Man Barlo fishing quests. If you've done all five of them, this achievement lights up. This achievement was lit up for me immediately upon entering Beta without having to do them all again.
The most interest achivement of all, though, is connected to the Stranglethorn Fishing Extravaganza. There is a "Master Angler of Stranglethorn" achievement but, frustratingly, it does not currently check to see if you've already won the tournament. It did not light up for me, despite me having in my possession and using both of the rewards available from the tournament. There are other achievements in the game that check for possessed items, though. For example, I got a "Feat of Strength" achievement because I have a really old, no longer available, epic mount in my bank. If the game can look for such an item, it can clearly look for others like bind-on-pickup tournament victory items. Hopefully, this will be fixed as Beta progresses. I submitted a suggestion on this, too.
That's about all there is to report on fishing in WotLK so far. I haven't even found a Grand Master fishing trainer yet, and I don't expect to see one soon. As we all know, fishing is never near the top of the developers' to-do lists, so it will likely be a while before fishing pools and new fish make it into Beta.
As they do, though, I'll keep you updated.