sharks can be ok with livebearers but you will need to watch the size of the shark and they do tend to eat the babies. i would reccomend against them in breeding tanks but in a community tanks, they can be a great addition. they can occationally be a little territorial so watch them to start with. They grow to be quite big fish and they need adiquate space so a think carefully before getting one. They are very nice fish to have though!!