I just avoid having male and female livebearers in the same tank because they're the mice of the fish world. However, I've found that any kind of danio (I typically use zebras) will voraciously devour livebearer fry. Generally speaking, zebra danios don't nip, I've kept them with close to everything. A buddy of mine even kept them with his betta sorority. They're decently attractive and VERY active. Also very easy to find, they're in every fish store I've ever gone to, that includes Walmart a poor excuse for live fish.