What I didn't see anyone mention was the fact that these can only be caught from Highland Mixed School of fish. These are pools that spawn and then disappear. YOU CANNOT JUST STAY IN ONE LOCATION CAN CATCH THESE. You have to hunt each lake area until a pool spawns, clear anything that you would aggro around you and then fish the pool. YOUR CAST MUST BE IN THE POOL OR YOU WILL NOT GET ONE. Then you will only get 2 or 3 and the pool will disappear and you start again.

check this link for great information: http://www.capsu.org/wow/catching_furious_crawdad.html