Tips to Fishing
I think there are since theres nearly always a sailfish spawn west of greater marrow, the wreckfish always spawn in 3 locations at shipwrecks (I think) in gale cliffs, theres a couple ghost and pale skate spawns in devils spine that always seem to be there (when not depleted of course), theres a searobin spawn right next to the charred pontoon and a frilled shark near the ancient temple, among other examples.
Even then, knowing which island the moon/sun fish are near would help.
You can use bait in the open sea to get both the sun/moon fish and their aberrations! This also helps to get the Viperfish abbs as well. You don’t even have to go far out either, I just went deep-water off the coast from the Rickety Pontoon and the lighthouse, spammed that bait, kept a few fish to restock fish and I was done.
A large spawn of Sailfish are just NW from Steel Point (when you make that node anyway). I threw the bait in that area and they appeared on the rotation.
Note that Sunfish/Moonfish aren’t always the first fish in a school. I’ve had squid and other schools have sunfish and the like as the second fish I caught.