Mermaids are not real. It is not possible to hybridize humans and fish.
Some people think that genetic engineering will someday allow us to create specialized human beings with gills, super-strength, x-ray vision, or whatever. But you cannot just turn genes back on that have been undergoing unselected mutation for millions of years. They just won't work anymore, even if restarting them would not screw up all of the other embryonic development going on at the same time (think of how much space in the neck you would need for gills, blood supply, and water flow - remember that we are not cold blooded like fish and require a lot more oxygen).
What is real is a very rare and usually fatal mutation where the legs are fused together. It also causes severe defects in the genitor-urinary system and other organs. You cannot arbitrarily modify a developmental system that took millions of years to evolve. Here is a real-life case, one of only 3 to survive:
Article on "mermaid" girl, with photo
Your question may seem dumb at first glance (which is probably why you got all of the silly responses), but could trigger a serious discussion of genetic engineering and what it means to be human. On the other hand, the fact that you have apparently not learned how to distinguish between fictional beings and reality is a serious indictment of our culture and educational system. BTW, angels, ghosts, fire-breathing dragons, leprechauns and alien abductions are not real either.