Part 1 of the series.
In the first part of this series, I covered most everything you need to know to get started with Fishing in Vanadiel. Part 2 will cover where and how to go about leveling your Fishing using what I've learned skilling up to level 81. Quite a few of the suggestions I've read in other guides just didn't work when I tried them myself, so I'll be incorporating those experiences here rather than just copying and pasting someone else's work.
Amateur Rank Fishing
As I mentioned before (scroll down to "The Hardware"), it's very much in your interest to have a Lu Shang's Fishing Rod. It's the second best in the game, allows you to target fish that are profitable more often while skilling, and makes reeling fish in easier as well. If you can't afford Lu's, get a Halcyon Rod instead and save for Lu's. I wouldn't recommend doing the Lu's Quest personally as you could sell Moat Carp to buy one off the AH with less than 10,000 fish. I also wouldn't recommend fishing up Moat Carp to pay for it either. Even without Lu's there are more profitable, low level alternatives.
So from here on out, I'm going to assume you have either Lu's or a Halcyon. Both will pay for themselves pretty quickly if you fish frequently.
Levels 1-5: Crayfish.
You can catch these in any fresh water in the starter cities and all over the place. Use Little Worms for bait. Buy the worms from an NPC in whichever town you're fishing at.
You will actually double your money at this stage, but spending 4 gil to make 8 gil isn't anything to write home about.
Level 5-11: Moat Carp
These will be your first Fishing Guild Rank Evaluation item, so hang onto one.
You can probably fish these up exactly where you caught Crayfish, but check the link to be sure. My personal favorite was Bastok Markets by the Goldsmithing Guild, but I see people in Windurst Waters reeling them in everytime I go there. Pick the scenery you like and have at it.
Knightwell in West Ronfaure is also a popular spot, but it's outdoors, so you can catch low level monsters ("Something caught the line!!!") so if you're only level 20 you may need to be careful.
Use Insect Balls as bait. They're a level 29 Cooking synth. Either make your own or buy some off the AH. (Always buy ingredients from NPC vendors to make your own.) Jeuno and San d'Oria will almost always have some in stock if you are going the AH route.
When you hit level 8 go to Windy to trade one in to reach Recruit Rank Fishing. Sell stacks of Moat Carp in Sandy or Jeuno. They'll go pretty fast for about 4-5k stack usually.
Recruit Rank Fishing
Level 12-17: Yellow Globe
For bait use either a Sabiki Rig at the North cliffs in Qufim Island (which will also catch Cone Calamary they go for 3-5k per stack on the AH) or try at the Ice Lake with a Worm Lure.
I'd go with the Sabiki Rig at the North cliffs, personally. It's got the advantage of being able to snag up to three fish at a time. You can buy both lures from the Fishing Guild in Windy or Aht Urghan. You could alternatively use Lug Worms, at either location but you'll catch herring and cod which may be too dificult to reel in.
This is also the first time you'll really see something odd: The vast difference in "fight" certain fish have. Cone Calamary are level 48, but you should be able to reel them in pretty consistently because they have next to no "fight" in them.
Once you hit 17 you can either go and catch a Cheval Salmon for your Rank Evaluation fish to trade in once you hit 18, or you can go straight to your next target and first decent money fish: The venerable Nebimonite.
To catch the Cheval Salmon buy a Fly Lure at the Fishing Guild (Whitegate's is probably most convenient for non-Windy citizens) and head to the creek in East Ronfaure. Turn one in once you hit 18. If you really want to you can fish these until 21, but they tend to be annoying to reel in, and sell for crappy money, so why bother?
Initiate Rank Fishing
Level 17(/21)-27: Nebimonite
Nebs are where you'll really start to make some money with Fishing. You can catch them primarily in two areas: The Selbina-Mhuara Ferry and in Sea Serpent Grotto at the lake below the Ornamented Door "overpass" looking thing on the first map.
There are pros and cons to either location.
The Ferry has a decent bite rate and you can catch Noble Ladies which gave me some great skill ups. Unfortunately, Sea Horror also spawns there and tends to kill most people who aggro it. There's also the occasional pirate attack and you may have one of the WHM Club NMs pop with them.
Aside from possibly dying unless you have Lu's you'll have to let go any "Something caught the line!!!" with three exclaimation points because they are either monsters (with a positive message as the second line) or Gugru Tuna (with a negative message on the second line).
You also have to stand around waiting for it to depart for a few minutes each time it arrives at a city.
Sea Serpent Grotto is nice if you have Lu's because you can also catch Bastore Bream and Grimmonites both of which sell fast and will give you some nice skill ups. There's no waiting time for the ship to depart either. Just straight up fishing. You can also nab Norg Shells which are easy to reel in and sell for quite a bit on the Bastok/Norg Auction House, but they're Rare so you'll need to run to Norg if you want to sell multiple ones.
If you're using Halcyon both fish will snap your rod like a twig though. Triple explaimation marks will be a Grimm with a negative message and a monster with a positive one. The monsters will slaughter a lower level character, and there's monsters that are Too Weaks at 75 walking around the lake area as well. Casting Sneak can eliminate both problems.
You'll need to decide for yourself which spot you prefer.
You may notice I haven't mentioned bait/lures yet. The problems of other fish biting above all have a simple solution: Use Crayfish Balls. Which you can make yourself or buy from the Guild Merchants in Windy/Whitegate. Unfortunately, in my experience at least, Crayfish Balls have had a HORRENDOUS bite rate. I'd be getting a bite on my line 1/10+ times. You'll have good and bad days Fishing, but for me personally I've had lots of bad with no good.
That's why I recommend going with a Shimp Lure. It takes ~50 Alchemy and ~20 Goldsmithing to make, so you'll probably need to buy from the Auction House or have a friend make you one unless you have the crafts leveled. They're used in the Mog Safe expansion quests, so you will probably always be able to get one from the Auction House.
Using a Shimp Lure you'll have to deal with the perks and penalties I mention above (besides monster aggro posibilities which are the same regardless), but you'll probably also catch more Nebs per hour and get bites from Noble Ladies on the Ferry. As well as be able to reel in Gugru Tuna/Bastore Bream/Grimmonites if you have Lu's for additional profit.
All the fish I've mentioned for this stretch are nice in that they move on the Auction House pretty quickly and will make you some gil. Save for Lu's if you don't have it already. It won't take long.
Level 27-28: Giant Catfish
Whether you really want to do a full level on these or not is up to you. You'll need one for the Guild Rank Evaluation though, so catch at least one and trade it in once you hit 28.
I've had good luck with a Minnow at the West Sarutabaruta Pond.
28 = Guild Points!
I should also mention you can now start getting Guild Points to buy key items and Fishing Armor. The sooner you start the better. Well, if you want something you need GP for anyway.
Things Get Tricky: Novice Rank Fishing (and Beyond!)
As I said in the first installment: Fishing Skill doesn't do very much. Which means that what you fish for skill and profit should usually be the same thing. And they usually can be especially with Lu's in hand. So, instead of saying, "Go here. Fish up these using this bait." From here on I'll highlight some fish that are good for skill and profit, whether you must have Lu's for them, and how much "fight" they have to them.
Note: If you can get an Albatross Ring it more than doubles the amount of time you have to reel in fish and makes skilling up possible on fish you couldn't otherwise reel in in time.
Level 42: Gugru Tuna (Lu's only*)
If you have a Lu's and like the Ferry keep on riding it! You can get to 42 off Gugru Tuna using a Shrimp Lure. If you get a !!! fish with an insane amount of fight to it you have a Ryugu Titan on the line. If you managed to reel it in it could snap Lu's, so let it go.
(*) You can try using a Composite Rod to fish up Tuna, but you'll lose stackable fish to "too small" messages and probably have a hell of a time reeling them in in time. I haven't done this personally, and don't recommend it.
Level 48: Cone Calamary
You've probably caught some of these already. I'd be kind of surprised if you hadn't. Sliced Bluetail in North Qufim should only get these, Gigant Squids (three exclaimation marks; negative message) and monsters (three exclaimation marks; positive message). I wouldn't recommend it too highly though. I suspect you'll suffer from low bite rates and lousy profit.
Level 53: Shall Shells/Istiridye
Grab a Rogue Rig or Robber Rig and hit the beaches in Valkurm, Bibiki Bay, or if you crave adventure, Cape Terrigan.
Alternately, head to Nashmau with the same. Be warned though, ToAU/WotG area fish have much higher stamina making them harder to reel in in time. You may want to stick to Zilart areas unless you have an Albatross Ring.
If you have ~60+ Bonecraft you can make pearls out of these with a Wind Crystal, or put them on the Auction House (ToAU ones may sell slowly), or NPC them. They'll definitely make you money.
Level 55-90: North Qufim (Lu's required)
I've got to mention this because as a Fisherman/Chef it's one of the best Fishing spots in the game. You can catch Cone Calamary (which may still skill you up at this point), Bluetails which have a good bit of fight to them, and Gigant Squid which despite being level 90 are easy to reel in.
Sure "North Qufim" isn't a fish, but it's so freaking awesome fishing it deserves special notice here.
Level 61: Bhefhel Marlin
These are the fish that can contain Pirate's and Brigand's Charts when traded to Zaldon in Selbina. Albatross Rings are 100% drops from the easy pseudo-BCNM at Valkurm Dunes's west beach, and make Nashmau/Tallaca Cove fishing much easier.
To catch them use Sliced Bluetail. You can cook up your own or buy them from the Guild.
I like to fish North Qufim for skill/profit and then turn some of the Bluetail I catch into Sliced Bluetail when I need bait to get another Albatross Ring or want to try for a 4.5 million gil M.kris dagger. You can also just buy the fish off the AH. Check to see which will be cheaper at the time, it varies.
Silver Sharks will also bite and can be traded in to Zaldon as well.
Level 63: Trumpet Shells (Lu's)
I've fished these up a bunch of times. If a stack is selling for 50k on your server it may still be worth the time, but otherwise the bite rate tends to be bad, so I'd stay away.
A Closing Note...
I'm going to leave it here for today. If you're starting out Fishing you'll be busy getting to 60 for quite a while.
I also want to point out that if you're in the 30s and catching Nebs for money you really can just stick around there and continue to skill off Noble Ladies. If you don't have Lu's yet it limits your possibilities quite a bit, so getting skill ups while you save for it isn't bad.
And once you hit the 50s with Lu's you can literally park yourself in Nashmau and hit 100 Fishing there.
So just take your time, relax, and enjoy yourself. Happy Fishing!