Just a quick note – and this is absolutely not a fancy strategy, and I can’t believe there aren’t more people doing this on my server (but then again, the less people doing this the more profit for me).
Whenever I’m in Deepholm, I make sure I fish some Albino Cavefish. It’s only used for one thing – Deepstone Oil, from Alchemy – but every alchemist will be making a handful of those for skillups, plus they’re reagents for the Vial of the Sands mount.
The Therazane dailies (which I do for reputation, gold and the chance at achievements – although I still haven’t seen the Pebble daily nor the Fungalmancer Glop daily, grrr) take me right to a place with plenty of pools (the Crimson Expanse, at about the 3-o’-clock position on the map), and I’ve never seen anybody else fish these pools. There are also some pools further south, at the Silvermarsh, but I rarely bother with those.
There are red clouds on the shores that will put a DoT on you, but it’s quite easy to avoid those with some method of water walking. (If you’re not a shaman, priest or death knight, try the Elixir of Water Walking – it can be found in the bag rewarded by the fishing dailies, so it’s pretty easy to obtain.)
The price has remained pretty steady on my server, at 8-10g per fish (160-200g per stack). I only fish what pools I see while doing the dailies in the Crimson Expanse area; it takes about 15 minutes of my time per day, and I usually come out with one and a half or two stacks of the fish. Considering I still don’t have fishing capped and I’m still missing the Sea Turtle (and it’s been confirmed to drop from Cataclysm pools, thank you Blizzard for small mercies), it’s not a bad gold return for something I’d be doing anyway. By the time I log in to do my dailies, the fish I caught the day before has sold; there is very little competition.
Sure, I could be fishing for Fathom Eels in Uldum – but that’s a pain, since the fishing pools are affected by phasing and as a result there’s a whole clump around Schnottz’s Landing. There’s also plenty of competition, the fishing path is long, and the prices keep dropping to the point that on bad days, they’re below the Albino Cavefish. Other fish has similar issues.