As a Fisher looking for water crystals, you have two readily available options : Caiman and Thaliak Caiman. Caiman are available from 6PM-9PM in Voor Sian Siran and The Iron Feast, while Thaliak Caiman are available from 3PM-5PM in Middle Thaliak River. In all three cases, they're mooched, most easily either from Blueclaw Shrimp (at The Iron Feast) or Bullfrogs (Voor Sian Siran and Middle Thaliak River).

There are two tricks. First, you can choose a bait that focuses on the mooched fish. Blueclaw Shrimp are the only fish at The Iron Feast that will bite on stonefly nymphs, while Bladed Steel Jigs get Bullfrogs more than half the time.

The second is to boost your HQ rate as high as possible. Perception food helps, but more important is use of the Patience (or Patience II) skill. Don't waste Hooksets on the Bullfrogs/Shrimp, but you'll want to do so on the mooch. (I'm pretty sure powerful hookset for both.)