well, what else do you that is not a mbuna like the zebra? Mbuna are way more aggressive than anyothers... mine was not the most aggressive, but it could have been if there was not another zebra being more aggressive, he did attack anything new I put in... they as a group like 7 killed my first front, another mbuna (colbat blue) and a peacock, that I had raised since a baby in the tank... Since I have moved them out of my tank I have lost no fish, and they have not killed each other in their new tank either... so in the long run yes, I have had that problem too...