Fishing in Cata (and maybe even before) will be an important skill. Not only will it be needed for the guild perk for the new fish feast, but it will be an important source of volatile water.
Fisherman can help this by fishing up Glassfin Minow from the lake/river in Crystalsong forest, selling these to alchemists who can make an Elixir of Water Walking. DK's and Shamans (and maybe Priests) can all walk on water and fish
Engineers can make Aquadynamic Fish Attractor to give +100 fishing.
I expect demand for both of these items to skyrocket before cata hits.
UPDATE: Blizzard fixed the issue that made Elixir of Water walking a must have. It is still worth stocking up on fishing aids, but no longer essential. Yes I knew something I didnt say.