So I found out about so-called fishing hot spots yesterday -- places where you fish almost exclusively blue and gold fish. There's one in the ocean near Velia and I made over 1 million silver last night from afk fishing and another 300k this morning.
Here's a map (http://digfordiamonds.com/map/) and here's a reddit thread talking about them (https://www.reddit.com/r/blackdesertonline/comments/4b78ty/fishing_hotspot_megathread/)
You'll notice the gold fishing spot on the map near Velia -- if you head out there you can't miss it -- there will be a major cluster of boats -- so many that I had to be careful when I dismounted from my raft not to end up on someone else's boat.
Warning, I did get auto-disconnected from the game several times rafting near that spot -- I'm assuming the game is having difficulty handling hundreds of people all in the same place.
The map also appears to show treasure chest spawn locations but I haven't checked them out yet.
I read in various other places that the hotspots aren't always active, may change weekly or monthly, and that they might be nerfed because they are slightly ridiculous at the moment -- these are all wild rumors which I can neither confirm or deny.
Fitz