1. Download this: MrFishIt.
2. Go here: WG Underwater Fishing Location.
3. Make sure you have 40+ bag slots.
4. Turn on the bot, tuning the settings so you don't loot junk.
5. Go sleep.
6. Wake up
7. Go to AH, put up everything you fished 1g cheaper for bid/BO prices.
8. Profit.
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I usually get a lot of fish stacks, and 1-2 Siren's Tear from the clams. 1 Day I got lucky and got 4 of them (!).
On a note, not only you get gold, but also honor and marks from WG battles.
ALSO, can be used for skilling up Fishing 1/450 in 2 nights.
OPTIONAL:
Use an Auto-Reply bot if you have players that do this on your realm.
Here are some pics; note that I also had Siren's Tear left from opening clams that I didn't sell, it can be sold to up to 100g on my realm; so that's 100g more.
Before opening mails from AH:
After opening mails from AH:
***SAFETY NOTE:***
The bot is undetectable by Blizzard. You WON'T get banned, except some other fisher gets there and he is nasty. I'm doing this for 1 week already, and I even haven't got a single whisper from a player.