Highly depends on your server man, on my server fishing is pretty good money with the right fish. What you need to do is look at prices of say Elementium Ore/Cata Herbs/Fish like Fathom Eel/Highland Guppy and then look at what you can gather per hour, this will give you a baseline of gold per hour then simply do what is most profitable.
on my server the fathom eels are selling for atleast 240g a stack, since you can fish 20 in 15 minutes its pretty profitable but they get farmed quite alot.
Baseline: It is profitable, the question is in what degree compared to other proffs - only the AH can tell you that.
