FFXIV Angler is already pretty complete in its information, especially because it compiles information on catch frequency based on user input presented as percentages. As such, it's a very good estimator of your RNG. It has info on lures, fishing spots, fishing chances and even desynths and Aetherial reductions. It even has a bar graph that shifts depending on a semi-real time measurement of Eorzean Time.

It's basically the fisherman's bible.