Fishing has always been a good idea. The way this is presented would work. As for a place to fish, it would need to be large to accommodate for the many players that would want to fish, especially for an income. A new town would be great.
I talked about fishing with many people, I think it would be ideal to make it a daily quest and not something to do freely for hours at a time like looting or bug hunting or farming.
Right now I think it's a tad too tedious trying to earn gralats. Bugs are cheap and not as prevelant as before, which was a major income for me back then, and looting. Looting is okay, but it's still tedious.
An extra way to make gralats is always a welcome idea.