Hey - here is a quick fishing guide that I have been practicing - it probably can use some edits. Plus I have the "records" for my game - would love to see if you have higher...
Fishing - just exit/reenter the screen to look for the size fish/type of fish you want. Saving the game on the beach will change the fish in the water as well. You can usually tell if there are large rockfish, tuna, hammerheads, marlins or great whites. Perches are too small to tell.
Seaperch - Weight: 5.61 lbs - USE: natural jig but will even go after heavy squids.
Rockfish - Weight: 30.93 lbs - USE: natural jig but they may go with other bait also
Tuna - Weight: 110.55 lbs - USE pink squid
Hammerhead Shark - Weight: 1086.97 lbs - USE pink jig (heavy)
Marlin - Weight: 1036.82 lbs - USE pink squid (heavy)
Great White - Weight: 2260.45 lbs - USE pink squid (heavy)
Sometimes if the color listed doesn't work, just try another color.
There is no rhyme or reason to fishing, it appears. Sometimes you catch them, sometimes they steal your bait. I find fishing near the middle of the beach works best and when they are not bumping up against the jetty. You usually catch them when they come up behind your bait and not from "north" or "south".
You can make some good money with big fish.
As I can figure, hammerheads and great whites are the most rare - hammerheads might show up once every 100 views of the beach and great whites even less. Marlins maybe 5%.