There were? ways of seeing which blocks have fish, If you click on blocks while holding a chisel only the normal stone gets changed, fish remain stone!
When you get the thaumometer and scan the stone the fish blocks show up differently,
these may have been patched, its been a while since I played.
I know I died plenty of times to fish, I did become very careful, using the chisel, leaving a block hole, so they'd get stuck in it if they did spawn. I tend to wade in so I died quite a bit, I learnt to run away more!