Once again I'm gonna say 8. I thoroughly enjoyed the episode. Loved Mariner's obsession. Loved the parasite reveal.
Loved the subplot with Tendi and Rutherford. And the stuff with he fish aliens was entertaining too.
Particularly enjoyed the reference to the Edo.
And the way they played with the cliches of the "jealous boyfriend" plot.
And unlike in DS9 were Kyra spent a whole, painful, episode trying to talk this one old guy to move from his moon...Freeman, upon finding out that the one fish guy and his wife were the only inhabitants of their moon, just told him to screw himself and went ahead with the plan.
Loved that.