i'm pretty sure they're ghost shrimp! i have some floating plants for the fry; i also wondered how nocternal the ghost shrimp are. They're quite fast when they want to be, and I *do* worry about the frys' ability to outswim them should they get hungry. My platy had six today (!), and they're still in the "birthing box" in the 20 gal; I have two in the fry tank that are 3 weeks old, and one that is 2 months--those, I think can stay out of the way. It's the newborns I worry about...