Ok so there is a merman. I‘m not going to say anything else and spoil this but this is not a fantasy book. It has a more sci-fi vibe to it. It‘s an interesting story and brings up some good science/medicine-based ethical questions if you‘re that sort of person.
There is mpreg but it‘s part of that sci-fi vibe and science/medicine-based line of thinking. This is not an Alpha-Omega story.