i wouldnt say enemy's but the mbuna prob will not tolerate a larger fish in his territory so he will probably nip the frotosas fins like crazy forcing the frontosa to feel uncomfortable and who knows how long he will tolerate that from a fish that can easily fit in his mouth. the mbuna will mature faster than the frontosa will grow so it will be a one sided battle for a long time. those 2 fish species would never encounter each other in the wild. im not a fan of mixing the different lakes when it comes to african cichlids. i would pick 1 type of cichlid for now and see how you do. there are many types of mbuna you could mix that i see people do all the time. adult frontosa need a 6 foot tank and much mellower tank mates.