They're not like mining or botany. You can always fish in a certain location as long as you have enough baits/lures. Although gathering fatigue will be an issue if you fish too much within short time.

The reason your fishing "hole" disappeared is because that was actually a spearfishing point (where you used off-hand tool), rather than a fishing pool (where you should use main-hand tool).

I suggest you go to Grade 2/3/4/5/6 fishing pools at Rank 3/13/23/33/43 (assuming you have good gear) if you want both SP and fish; or you can simply find a safe Grade 10 spot fishing since R1 till R50 if SP is your only concern.

For where you can find Grade 2-10 fishing pools, please check http://www.disciplesoftheland.com/Maps.aspx