I wouldn't worry about finding out there are other mermaid acts going on. It's really hard not to overlap but there are so many different ways to interpret a theme! I do an act where I made a giant televison with a tracing-paper screen where I crawl out of it all creepily like the girl in "The Ring" film before stripping in a more conventional burlesque manner. I've done the routine twice now and was just about to put it up on youtube but then I saw that someone else had done this theme too but in a very different way! I was still gutted, I thought it was completely origional - I had googled the idea and everything but nothing had appeared. It really is difficult but good luck with it,
xx