Stage 0.5: Nebimonite
Fishing Levels: 0-27
Area: Ship between Mhaura/Selbina or Sea Serpent Grotto
Bait: Halcyon Rod (or Lu of course) & Crayfish Paste
Notes: Skip moats and hit these up for 27 levels. They sell incredibly fast on the AH for about 9k per stack. To save more gil, buy the crayfish paste at the fisherman's guild for dirt cheap. I'm sure they were exaggerating, but people said they made almost enough to buy a Lu from AHing these from 0-27 instead of spending time on Moats and random other fish. I imagine if you would like you can start Istiridye earlier than 27 assuming you have a Lu, a friend began them at level 7 with a Lu.
Stage 1: Istiridye
Fishing Levels: 0-53
Area: Nashmau
Bait: Robber Rig
Notes: These are incredibly easy to reel in and stack. If you are a bit patient they will sell on the AH for 7k a stack, or find a high level bonecrafter who synths them into black pearls and sell to them directly for a negotiable price. They also NPC for 300ish gil. I made 70k my first day just NPCing these while racking in a couple fishing skill levels from 30-33ish. I currently dbox them to a high level bone friend for 5k a stack.
Stage 2: Mercanbaligi & Ahtapot
Fishing Levels: 53-86
Area: Nashmau
Bait: Shrimp Lure
Additional Location: Tallaca Cave, W exit of Nashmau through Caederva Mire near Einherjar entrance.
Notes: A friend prefers Tallaca Cave, the difference is in Tallaca you will also fish up Dil's which you will not in Nashmau. NPC rates seem to vary on these from about 600g on Mercs to 700gish on Ahtapots. Mercs are the Eastern equivalent of Bastore Breams and Ahtapots are the Eastern equivalents of Grimmonites. Dil's npc for almost 800g each and are the eastern version of black sole which cap at 96. I personally prefered Nashmau until the Ahtapot cap at 90.
This is where a few options seem to open:
Stage 3 Option A: Pterygotus
Area: Nashmau
Fishing Levels 86-99
Bait: Lugworm
Notes: Biterate is acceptable, and these will not break a Lu.
Stage 3 Option B: Dil
Area: Talacca Cave
Fishing Levels: 86-96
Bait: Shrimp Lure
Notes: You will also hit Mercs (single !) which are already capped, and also Ahtapots (!!!) which cap at 90 but the bite rate of hooking dils is similar to Pter's and you will make nice gil off the other 2 fish in the meantime.
Stage 3: Option C: Cave Cherax
Area: Quicksand Caves
Fishing Levels: 86+ or more likely 99-100
Bait: A MEATABALLS
Notes: These will snap a Lu Shangs and/or your line. If you go this route and do not have WW high enough to repair consider buying multiple Lu's.
Stage 4: Option D: Armored Pisces
Area: Oldton Movalpolos
Fishing Levels: 86+ or more likely 99-100
Bait: Sinking Minnow
Notes: These *will not* snap a line or rod if the fish is completely depleted. Bite rate seems to be equal or possibly better than Cave Cherax.
Stage 5: Option D: Lik/Gugs
Area: Lufaise Meadows, Open Sea Route Mhaura/Al Zahbi
Bait: Minnow, Meatballs
Notes: If you are lucky enough to have an Ebisu by the time you cap Ahtapot 90 in Talacca Cove skilling off these is a profitable option. I personally skilled 90-100 off Liks and made quite a fortune bazaaring some for 15k and unloading others to lsmates for 10k each and helping them obtain an ebisu. This really wouldn't be a great idea if you had a Lu, but if you were lucky enough to have an Ebisu at this point, the skill ups were quite decent.
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TLDR Fishing for Dummies Version:
All done in Nashmau:
0-53 Robber Rig, Istiridye (If no Lu, then Nebs until 27 w/Halcyon)
53-86 Shrimp Lure, Mercanbaligi & Ahtapot
86-99 Lugworm or Sinking Minnow, Pterygotus
99-100 QSC, Meatballs/Cave Cherax OR Oldton Movalpolos, Sinking Minnow/Armored Pisces, OR Lik/Gugs Minnow/Meatballs
this is all it had.