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If I'm not mistaken, once you update the game, the fish should spawn. I don't think they are entirely tied to new terrain generation, but I'm not completely sure.
The wiki doesn't explain much because it describes things as if you were already playing this version of the game. If you want to wait for someone with deeper knowledge of how the game works to answer you, that may be better.
Either way, there is the possibility to export your buildings as objects, then update the version, and import your base again so you don't lose it (if you want the new terrain generation to apply after updating).
I didn't check if this was answered in another post before, but maybe you should search for it just in case.