Pandaren Angler

Catching 2 fish with [item=85973] activated still only counts as 1 towards this achievement.

Thankfully for smaller guilds [like my own] there is no feast recipe attached to this achievement.

Just like the new flask achievements in MoP, the removal of both cauldron and achievement based feasts, means that for the smaller guilds their is now a much more fluid accessibility to these tools to better raid or pvp (whatever floats your boat).

The removal of cauldrons as a whole seems a bit strane on blizzards behalf, but in a cooking sense, the new banquet system of cooking is much more accessable to all players and not just ones who are part of hugely populated guilds with avid fisherman.

If your guild has low amount of fish already caught, then here's some handy guidelines for a cost and time-efficient way to tackle this achievement.

So say your guild already has about 500 fish caught from pools. It's best to start off going for Pandaren Angler by fishing in Pandaria, because not only are you getting high-level fish for yourself and the guild, it is also counting towards That's A Lot of Bait and We're Gonna Need a Bigger Boat, so it's conveniently progressing towards 2 other achievements too! This also nets the guild a Cata recipe that is useful for those trying to obtain all Cooking recipes.

If the guild also plans to attack Like Shooting Fish in a Barrel, then it is best to go back to Northrend. It is best to fish for the Fish Feast mats, as this also counts towards Dinner Party if it hasn't been completed already.
The best places to fish for these schools are:
Glacial Salmon-Blue Sky Logging Grounds down to the river before it flows into Venture Bay.
Musselback Sculpin-the large lake to the NE of Warsong Hold, plus the small lake to the East of Amber Ledge
Nettlefish-All along the may rivers and lakes connecting to River's Heart.

Additionally, this video http://www.youtube.com/watch?v=4DRdgKWJcMQ is useful for those last thousands you may need. The quest isn't required to created the Pools of Blood, but it may be useful if you want that extra bit of gold or the quest bag reward.

Update: In Patch 5.2: The Thunder King, a new small daily fishing event, 'Fish of the Day', was added. Ben of the Booming Voice will tell you where the current 'fish migration' is, and when you arrive in, say the Fields of Niuzao, you will find a huge amount of pools. This is a great way for fishermen in your guild or avid fishers to increase the count for this achievement without having to constantly fly around. A Large pool may also spawn some time, and this can be fished more times than your standard smaller pool. However, the Large pool will eventually despawn and Krakkanon will appear in the water. Krakkanon's loot is definitely useful for people that want Nat Pagle's daily fish or the hard-to-obtain Nat's Fishing Journal (seeing as it's obtained at Good Friend, which is essentially Revered for a friendship).
For more information on the event itself, check here: http://www.elsanglin.com/fish_of_day.html