Second Gym as in Shizui, or in general? Because we don't know how many Pokemon Shizui uses yet.
I'm sure he'll have an Oshawott. Shizui deserves the best Pokemon around, after all. I think he may also have a Clamperl or one of its evolved forms since he seems to specialize in deep-sea Pokemon. At least, that's one of the theories that I've read, but it made sense to me.