Once you have fished certain fish from the pools of Northrend, you earn the acheivement, Northrend Angler.
Borean Man O' War School: Borean Tundra
Dragonfin Angelfish School: Borean Tundra or Dragonblight
Fangtooth Herring School: Howling Fjord, from School of Fish
Glacial Salmon School: Grizzly Hills, from Fishing Pool
Glassfin Minnow School: Crystalsong Forest
Musselback Sculpin School: Lake Kum'uya in the Borean Tundra. Which is West of the D.E.T.H.A. camp, just off the road.
Nettlefish School: Sholazar Basin from Fishing Pool