Thank you for giving the context.
Is this for something you are writing, or did you see these sentences somewhere?
If the man asks "Where are all of the pretty fishes?", we know he has some particular pretty fishes in mind. For example, maybe someone told him that there were pretty fishes at that part of the shore, or he saw pretty fishes the last time he was there.
If the man asks "Where are there pretty fishes?" then he is asking where to find pretty fishes. He doesn't have any idea where to look, and he is looking for any pretty fishes, not a specific group in a particular place.
(I would use 'there' in this question.)
I hope I understood your question. If something still needs to be explained, please tell us.