I have three worlds. Grizzleheim, Kropotopia, and Wizard City (of course!) and I'm pretty sure all worlds in the spiral have fish. (if not MOST of them do.) In my opinion Kropotopia has the rarest fish in the ice vault. I think Grizzleheim has the MOST fish though.
I'm sure that as time goes on there will be more fishing areas, and more types of fish, added to other worlds in the spiral. There are areas in Celestia, Zafaria, Avalon, Azteca etc. that just SCREAM for fish to be added to them! There are also areas where there will probably never be fishing. Marleybone for instance. We'd have a hundred people crowded around that little fountain in Digmore Station. Give it some time and more fish will appear. My guess is that the KI folks just didn't want to hit us with too much goodness all in one fell swoop.
I have three worlds. Grizzleheim, Kropotopia, and Wizard City (of course!) and I'm pretty sure all worlds in the spiral have fish. (if not MOST of them do.) In my opinion Kropotopia has the rarest fish in the ice vault. I think Grizzleheim has the MOST fish though.
I have found this in three threads :O can you tell me what fish you caught
KI is currently working on making more worlds with fish, I think KI wanted to at least launch the Fishing Update early but not with all the world having the ability to fish in them. Also KI would need to think up of more fish, what areas to make the fish, etc. KI will probably finish making fish for all the worlds that can have fishing in mid 2015 (I think). Also some places don't include water so fish cant be fished in those areas.