Best place to catch is Talacca Cove (W exit of Nashmau through Caedarva Mire) or Nashmau. Shrimp lure catches Dil (Black Sole, Talacca only), Mercanbaligi (Bastore Breams) and Ahtapot (Grimmonite).
Standard Merchant Resale Price: 600 - 714 gil
Guild Resale Price: 675 - 900 gil
If you NPC these, you get around: 7200 - 10800 gil for a stack. It really doesn't end up being worth someone's time to put them on the AH for less then 10k gil in my opinion. It's one less slot to sell something for better profit.
Sold to NPC for 600~ gil, which means you make 7200 gil a stack from selling to NPC. They are rarely sold on AH, this fish is good both for gil and level up your fishing.