Rod - Halcyon
Bait - Minnow
Location - Ferry (there may be slightly better areas but with a minnow this also allows access to cone calamari and noble lady too which are good to AH)
These are used to skill cooking, good to NPC, great to auction house but my favourite is slicing these up and they make fantastic Bhefhel Marlin bait with a composite rod.
Recipe: (Cooking level 15)
1 x wind crystal
1 x Bluetail
Yield:
4 x Slice of Bluetail (only a NQ tier, no HQ tiers similar to paste or yagudo drinks)
Selling to the Fishing Guild merchant on the boat can net you ~350-450 per fish or 4200-5400 per stack. Putting a stack up on Jeuno costs around 250 gil plus the time it takes to sell. Always check the Guild merchant first before you go to the AH.
Shows the mentality of the Siren dolts. These NPC for 6k stack these dummies undercut each other and sell at a loss. The knock on of this is none in the ah and the price of Fish Oil Broth doubling in 1 week to 20k.