Quest: Fishing
Requirements: Level 35, 225 Fishing.

You need to go and find Nat Pagle in Dustwallow Marsh. He is standing on a small island to the West of Theramore (58,60). He'll ask you to catch four rare fishes for him. This quest is actually really easy and the only hard part is the amount of travelling involved.The fish you need to catch are:

Feralas Ahi - West from Camp Mojache. Fish the Verdantis River where the small bridge is by the Ogres, you'll soon catch one.

Sar'theris Striker - South or North or Shadowprey Village. Make sure the area comes up as Sar'theris Strand.

Savage Coast Blue Saffin - Just outside Grom'gol Base Camp. Make sure the area comes up as Savage Coast.

Misty Reed Mahi Mahi - Directly East from Stonnard. Just avoid the Murlocs.

You should catch these fish within 5 to 10 casts at each location. So it wont take long. I haven't done this quest on my Alliance character, so I'm not sure of the best order in which to do them.
Now go back to Nat and get your Artisan Fishing.

Go to Steamwheedle port and speak to Gikkix, You'll want to buy the following two recipes: Spotted Yellowtail and Poached Sunscale Salmon.
Either fish for Spotted Yellowtails at Steamwheedle Port or go to Raventusk Village (well not to it, just a little North of it) for the slightly better drop rate. You'll need about 30 to get your cooking from 225 to 250.
Now go to Bloodvenom Falls in Felwood and fish for Sunscale Salmon. You'll need about 30 to get your cooking from 250 to 275.
No go and speak to Vivianna in The Feathermoon Stronghold and buy the recipe for Mightfish Steak. Whilst your there buy about 40 Hot Spices and 40 Soothing Spices as your going to be making the food that you will want as a level 60 (without going into instances that is). It gives a +10 stamina buff for 15mins which is always helpful.
Now go to Scalebeard's Cave in Azshara (its one of the islands to the East) and fish for Mightfish. You'll need about 30 to get your cooking from 275 to 300. You may need to bring some lures with you at this point, as your cooking will level up faster than your fishing and Azshara is a 250+ fishing zone. Once your cooking is a 300, keep fishing till you've maxed out that too. It will take 7 to 10 catches to get one skill up at this point, so take your time.