I have had one tropheus duboisi in a tank with other African cichlids for a few months. He (or she?) is about 3.5". He has been acting fine, occasionally chasing around other fish but that's expected. I have quite a few different types - kenyi, yellow labs, venustus, peacock, bumblebee, red empress, and auratus. I had 3 male kenyi (the yellow striped ones) and within the past 2 days he has killed ALL 3 of them. I know it's the tropheus killing them because he kept chasing them around. Now that they are all dead, he has started chasing the yellow labs, so I assume they are next. I just put him in a breeder net in the tank until I decide what to do. Is it strange that everything he has killed/targeted has been yellow? He is dark blue with a white/yellow stripe so he looks nothing like them. I don't know what to do with him. I have two other tanks but they are not as aggressive (one tank is south american cichlids & one is fry) so I can't put him anywhere else. Any reason why he is suddenly turning into a killer?