User blog comment:Zori9/Could Zoro Have Fishman Ancestry?????/@comment-4800978-20120326013312

Well, I'll give you points for creativity, this definitely is a new one. And when you consider how fishman genetics work and use Chimney as an example of a human/merman hybrid it can seem very likely.

But unfortunately I don't think this is the case, it just doesn't sound like a relevant plot point to explore/reveal now.