Originally posted by Desjovic:

lol you lucky guy, from what I heard there is only one (1) frost cave with a lake in the entire map per seed. But word on the street is you need the Cold fishing bait that can be made at the cauldron using Tuna.

I had 6 maps created before the update and not one cave with pond on any of them. Someone gave me a seed that had one & since then I have found one more on a random seed I created after update. I picked up most Tetra after they jumped out and caught the rest on the line with Cold bait. Sadly they do not seem to respawn, even after leaving game running overnight. At this point as Jwilly says they don't do anything so really not much point in chasing them, however it seems likely there will be more to the Mistlands eventually [level 4 gear hopefully] so they might be useful one day. Good luck find the cave pond though.