Another tip to go for:
Nashmau -> Halcyon (if you don't have a Lu) -> Robber or Rogue rig.
Target: Istiridye (eastern shall shell)
Cap at 53
They have an insanely high biterate (I catch about 2 to 4 stacks per hour), NPC for 300 gil each and if you have bonecraft leveled there's some more money to make out of them by desynthing them into pearls.
Cancel everything that "You have a bad feeling about" since it usually breaks your line.
Otherwise I think you're experienced enough to notice the difference between items and the real fish.
Wouldn't recommend putting them on AH as they sell slow as hell.
No offense, but everything about this screams "don't bother with this" to me. Please don't take this personally, it's just that it is so easy to both skill-up and profit with fishing at these levels.
Unless you have bonecrafting leveled to the point that you can reliably turn these into pearls or black pearls, you're going to be pulling in a low 3.6k / stack on these. Shall Shell have the same exact bite rate I'd bet in Buburimu (I've caught HUNDREDS), and they sell for 8k / stack, or you can use them to make fish mithkabobs if you've leveled your cooking to 49+. Either way, you will make more money on Shall Shells, and they are very fast and easy to catch. Grab a halycon rod and a robber rig and head to buburimu. I preferred the beaches near Bibiki Bay as I always liked watching the sharks.
Some cooks will possibly be pissed off at me for this, but I'm currently pissed off at a few undercutters so I don't really care. Here's what I did from 40-54+.
Catch 4 stacks of bluetail, head to buburimu (or you could just do this in buburimu if you don't like batallia)
Catch 8 stacks of shall shell, head to sea serpent's grotto
Catch 4 stacks of nebimonite, head to jeuno
Catch 4 stacks of bastore sardines
Buy 4 stacks of fire crystals (4k gil'ish), and turn those fish into 24 stacks of fish mithkabobs, or somewhere between 168k and 192k, plus the money you'll get from selling norg shells and damp scrolls. All that money, plus you will skill up quickly all the way to 55. This is for anyone with fishing in the 40s, not necessarily to the OP. He/she is apparently in the same boat as I am, which is past this glory phase.
Also, if you're a blu, you can cannonball the hecteye on the ledge at SSG and farm up some golden hakutaku eyes from the mindgazers while you're there for additional profit.
Another plus with the bluetails, as I've got high level alchemy, is that I was able to turn all of the cone calamaries into fast cash by making black ink and NPCing it. I actually made off better NPCing ink than auctioning it and usually pulled between 20-30k per session making the ink. But you'll only be able to do this as reliably as I did if your alchemy is 55+, which, comeon, it's alchemy... it's like cooking. Both should be at 60 if you're even attempting fishing.