As it may or may not be old news, I thought I share a very good tip or (cheat) to earning pelagos (money) in Endless Ocean Blue World.
As for me personally, I went to Cortica River Upstream South America in the Twilight Temple and I've learned that I can continually heal the fish there with my pulsar gun. The fish seem to keep multiplying with red, purple, yellow and green square marks. So in other words, I can heal the fish and make unlimited money this way; the easy way. This works well when I combine this with salvage requests and salvaging 20 items in my large bag or performing guided tour requests.
Just thought I share this tip for those like myself who are trying to save up 1 million pelagos to reopen Cavern Of The Gods.